Symbol Pu
Atomic number 94
Atomic weight 244
Group in periodic table IIIb
Boiling point 5,850°F (3,232°C)
Melting point 1,183.1°F (639.5°C)
Specific gravity 19.84
Electron Configuration: [Rn]7s25f6
Plutonium will be with us for a
long time, and not only because it has a radioactive half-life of 24,000 years
and therefore is dangerous for more than 200,000 years. Plutonium will be with
us because nuclear weapon states are deeply devoted to having it as a military
presence, the global nuclear power establishment is deeply devoted to pushing
it as the fuel of the future, and the personal and political opinions of
scientists often carry more weight than their scientific opinions.
This
emphasis on the military use of plutonium suggests that without the military
applications, support for “peaceful uses” of plutonium 239 would be meager.
Plutonium may be a nuclear weapons physicists’ dream (see sidebar), but the
dreams of physicists do not always come true, as is evident in the case of the
now defunct Superconducting Super Collider project of the 1980's.
So while
the pro-plutonium inertia is powerful, it is not omnipotent and the future of
this element and other special nuclear weapons materials is not set in stone.
As the debate continues to unfurl, it is important for people to know that this
most secret of elements is the most complex metal in the periodic table; and
its presence in deployed nuclear weapons threatens life as we know it.
Select
an element from the periodic table. |
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* |
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114 |
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*Lanthanoids |
* |
57 |
58 |
59 |
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**Actinoids |
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102 |
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Plutonium
belongs to the class of elements called transuranic elements whose atomic
number is higher than 92, the atomic number of uranium. Plutonium, named after the planet Pluto, was
the second transuranium element of the actinide series to be discovered in 1940
by Glenn Seaborg, Joseph Kennedy and Arthur Wahl, by deuteron bombardment of
uranium in the 60-inch cyclotron at Berkeley, California. Provided below is a short history of the
discovery of Plutonium.
----------------------------------------------------------------------------
Discovery
of the Neutron (1932)
The story begins in 1932, with the
discovery of the neutron by Sir James Chadwick, an English physicist. Until 1932, the atom
was known to consist of a positively charged nucleus surrounded by enough negatively charged electrons to make the atom
electrically neutral. Most of the atom was empty space, with its mass
concentrated in a tiny nucleus. The nucleus was thought to contain both protons and electrons because the
proton (otherwise known as the hydrogen ion, H+) was the lightest
known nucleus and because electrons were emitted by the nucleus in beta decay. In addition to the beta
particles, certain radioactive nuclei emitted positively charged alpha particles and neutral gamma radiation. The symbols for
these emissions are b - or –1e0, a 2+
or 24He2+, and 00g .
Twelve years earlier, Lord Ernest Rutherford, a pioneer in atomic
structure, had postulated the existence of a neutral particle, with the
approximate mass of a proton, that could result from the capture of an electron
by a proton. This postulation stimulated a search for the particle. However,
its electrical neutrality complicated the search because almost all
experimental techniques of this period measured charged particles.
In 1928, a German physicist, Walter Bothe, and his student,
Herbert Becker, took the initial step in the search. They bombarded beryllium
with alpha particles emitted from polonium and found that it gave off a
penetrating, electrically neutral radiation, which they interpreted to be
high-energy gamma photons.
In 1932, Irene Joliot-Curie, one of
Madame Curie’s daughters, and her husband, Frederic Joliot-Curie, decided to
use their strong polonium alpha source to further investigate Bothe’s
penetrating radiation. They found that this radiation ejected protons from a
paraffin target. This discovery was amazing because
photons have no mass. However, the Joliot-Curies interpreted the results as the
action of photons on the hydrogen atoms in paraffin. They used the analogy of
the Compton Effect, in
which photons impinging on a metal surface eject electrons. The trouble was
that the electron was 1,836 times lighter than the proton and, therefore,
recoiled much more easily than the heavier proton after a collision with a
gamma photon. We now know that gamma photons do not have enough energy to eject
protons from paraffin
The Compton Effect
When James Chadwick reported to Lord Rutherford on the
Joliot-Curies’ results, Lord Rutherford exclaimed, "I do not believe
it!" Chadwick immediately repeated the experiments at the Cavendish
Laboratory in Cambridge, England. He not only bombarded the hydrogen atoms in
paraffin with the beryllium emissions, but also used helium, nitrogen, and
other elements as targets. By comparing the energies of recoiling charged
particles from different targets, he proved that the beryllium emissions
contained a neutral component with a mass approximately equal to that of the
proton. He called it the neutron
in a paper published in the February 17, 1932, issue of Nature.
In 1935, Sir James Chadwick
received the Nobel Prize in physics for this work. It is interesting to note
that the Joliot-Curies’ misinterpretation of their results cost them the Nobel
Prize. (Not to worry; in 1935, they received the Nobel Prize in chemistry for
their discovery of artificial radioactivity.)
Chadwick's
Apparatus
The search was over. Chadwick had found a new elementary particle,
the third basic component of the nucleus. It increased the mass of elements
without adding electrical charge. Two protons and 2 neutrons made a helium
nucleus while 92 protons and 146 (or 143) neutrons made uranium, the heaviest
known element. This not only changed our view of the nucleus, but also provided
a new, relatively inexpensive means of probing the nucleus. Because the neutron
was relatively massive but neutral, it was scarcely affected by the cloud of
electrons surrounding the nucleus or by the positive electrical barrier of the
nucleus itself; thus it could penetrate the nucleus of any element.
Twelve years earlier, Lord Ernest Rutherford, a pioneer in atomic
structure, had postulated the existence of a neutral particle, with the
approximate mass of a proton, that could result from the capture of an electron
by a proton. This postulation stimulated a search for the particle. However,
its electrical neutrality complicated the search because almost all
experimental techniques of this period measured charged particles.
In 1928, a German physicist, Walter Bothe, and his student,
Herbert Becker, took the initial step in the search. They bombarded beryllium
with alpha particles emitted from polonium and found that it gave off a
penetrating, electrically neutral radiation, which they interpreted to be
high-energy gamma photons.
Playing with Neutrons (1934-38)
In
addition to the discovery of the neutron, 1932 was the year that the
Joliot-Curies first created new radioactive isotopes of nitrogen and phosphorus by bombarding boron
and aluminum with alpha particles.
The announcement of artificial
radioactivity created much excitement in the scientific
community. In the case of aluminum, the initial reaction with alpha particles
produced a radioactive isotope of phosphorus that then underwent positron emission to produce
silicon-30.
27Al13 +
4He22+
--->
30P15 + 1n0
The new radioactive isotopes were separated from the target
materials by radiochemical methods. Yields of the radioactive isotopes were
small because most of the alpha particles were repelled by the positively
charged nuclei.
In 1934, it occurred to Enrico Fermi, an Italian physicist,
to use neutrons to produce radioactivity instead of alpha particles, which are
repelled by the positive charge of the target nuclei. In Rome, his group
obtained a strong radon/beryllium neutron source and began to bombard the
elements in order of increasing atomic number, beginning with hydrogen.
Bombardment of the first elements in the periodic chart produced no
radioactivity, but finally a fluorine (Z = 9) target gave a radioactive
product. In the next 3 years, the group identified 40 new radioactive isotopes.
This work was important to the advancement of nuclear theory and provided
radioactive tracers for practically all of the elements. The use of these
tracers would later revolutionize chemical and biological techniques
The
group observed that when the target nuclei absorbed neutrons, they emitted
particles (alphas, betas, positrons, or protons) as well as energy, in the form
of gamma radiation. Thus, these nuclear reactions produced isotopes of elements
in the neighborhood of the target element. When Fermi's group reached the
heaviest known element, uranium, they expected that neutron bombardment would
produce transuranic elements
(new elements heavier than uranium) with properties similar to rhenium, osmium,
iridium, and platinum. Beta radiation from the products and an absence of
products that could be assigned to elements of atomic number between lead and
uranium validated their hypothesis. Thus, the products were assumed to be
transuranium elements.
In
1935, Otto Hahn, Lise Meitner, and Fritz Strassmann, in Berlin, confirmed the
uranium experiments of Fermi's group and also identified the presence of U-239
as a beta emitter with a half-life of 23 minutes. The Joliot-Curies
also confirmed Fermi’s work and, in 1938, identified a 3.5-hour radioactive
isotope that had the chemical properties of lanthanum, an element with an
atomic number much lower than that of uranium. They did not realize that it
was, indeed, La141, a fission
product. Another Nobel Prize blown!
These
results indicated that the nuclear reactions were complex and that the
Italians’ speculation of transuranium products might not have been entirely
correct. Furthermore, in 1934, Ida Noddack (a German chemist who, with her
husband Walter, had discovered the element rhenium) had warned Fermi’s group to
compare the chemistry of the "new" transuranium elements with all
known elements, not just those in the immediate neighborhood of uranium.
Noddack suggested that "when heavy nuclei are bombarded by neutrons, it is
conceivable that the nucleus breaks up into several large fragments, which
would, of course, be isotopes of known elements, but would not be
neighbors." The physics community ignored her warning, and she herself did
not follow up with experiments.
The
Italian group made one more important discovery in 1934. They found, by chance
and intelligent observation, that neutrons passed through a paraffin block
before reaching the target element were more effective in producing nuclear
reactions than those emerging directly from the neutron source. Fermi concluded
that the neutrons were slowed by elastic collisions within the paraffin and
that these slow neutrons were more effective than faster ones in producing
certain nuclear reactions.
It
is ironic that in 1938, while Fermi was
accepting his Nobel prize in Sweden, in Berlin, Hahn and Strassmann were
discovering nuclear fission. This work clarified the mysterious results
obtained from neutron bombardment of uranium and was the genesis of the atomic
bomb. It is interesting to reflect on what world history might have been had
the Italians recognized uranium fission in 1934.
The Discovery of Fission (1938)
By
1938, Hahn, Strassmann, and Meitner had identified at least 10 radioactive
products resulting from the neutron bombardment of uranium, many more than
Fermi’s group had observed initially. They assumed that these substances were
new transuranic elements or isotopes of uranium. The Joliot-Curies had also
performed this experiment and thought that they had observed thorium and
actinium (elements below, not beyond, uranium in the periodic chart). These
differences with Fermi’s results led both groups to continue their
investigations.
Early
in December 1938, Hahn and Strassmann thought that they had established the
nuclear reactions that yielded the products observed by the Joliot-Curies.
Presumably, isotopes of radium produced by the initial neutron bombardment of
uranium decayed to thorium and actinium. To be absolutely certain, Hahn and Strassmann
decided to identify the ‘radium’ isotopes by chemical means. (The chemical
separation is shown below.) The suspected radioisotope of 'radium' is indicated
as 'Ra'. Since
radium and barium are group IIA elements, having the same chemical properties,
barium was added as a carrier
to facilitate the chemical isolation of the small amounts of the suspected
'radium'.
The
final step in this procedure was a fractional
crystallization to separate the barium carrier from the
suspected 'radium'. Hahn and Strassmann were unable to separate the
radioactivity of the 'Ra' from that of the
barium fractions and thus confirmed that one of the products of neutron
bombardment of uranium was not neighboring radium, but distant barium. Could
Ida Noddack’s hypothesis be correct? Had the uranium atoms split into fragments
of approximately equal mass?
Hahn
and Strassmann repeated the experiment numerous times and were never able to
isolate the ‘radium’ from barium. They reported their results as follows:
"As chemists, we must actually say the new particles do not behave like
radium but, in fact, like barium; as nuclear physicists, we cannot make this
conclusion, which is in conflict with all experience in nuclear physics."
Hahn, the chemist, was reluctant to go against the ideas of respected nuclear
physicists, despite clear chemical evidence of barium
Hahn
then turned to his colleague, Lise Meitner, for an explanation. Meitner was a
physicist who had recently fled to Sweden to escape the Nazi regime. During
Christmas 1939, Meitner and her nephew Otto Frisch, a physicist also banished
from Germany, read Hahn’s letters reporting, with amazement, the barium
results. As Meitner and Frisch searched for an explanation, it dawned on them
that when the uranium nucleus absorbs a neutron, it might become unstable and
split into two particles of approximately equal mass (e.g., barium and
krypton). They used Bohr’s earlier model, which treated the nucleus as a large
drop of liquid. In this model, the absorption of a neutron could cause the
uranium nucleus to become unstable and divide into two smaller drops. If this
division takes place, the resulting drops (nuclear fragments) would be repelled
by their respective positive charges. This process, termed fission by Meitner and Frisch, would
create a large amount of energy, as well as additional neutrons. They
calculated the energy associated with pushing the two positively charged
nuclear fragments apart to be approximately 200 million electron volts (MeV)
per uranium atom. By comparison, the most energetic chemical reactions release
approximately 5 eV per atom.
From
where was the energy required to separate the uranium nucleus coming? Existing
data on the masses of the elements showed that the sum of the masses of the
smaller product nuclei was less than the mass of uranium. Meitner used
Einstein’s famous E = mc2
equation to calculate the energy associated with this mass difference (nuclear binding energy) and the
energy associated with pushing the two fission fragments apart. His
calculations revealed that energy equivalent to the mass difference was equal
to 200 MeV! Frisch quickly returned to his laboratory at the Neils Bohr
Institute in Copenhagen to experimentally verify this hypothesis.
The
scientific community was excited by the discovery of this new source of energy.
When Frisch presented his explanation to Bohr, Bohr is said to have struck his
forehead and exclaimed, "What idiots we have all been! Oh but this is
wonderful! It just must be!" Energy from fission was at least eight orders
of magnitude greater than the energy released in chemical reactions involving
an equal number of atoms.
Furthermore,
fission raised the possibility of a nuclear chain reaction. Radioactive fission products have
excess neutrons, compared with stable (nonradioactive) nuclei of the same mass
number. They can eliminate the excess neutrons by beta decay, a slow process
that increases the atomic number by one, or by direct neutron emission. In the
latter case, the secondary neutrons may be used to produce new fissions and if
a sufficient number of fissions occur, they will produce enough neutrons to
sustain a chain reaction.
It
was theorized that if such a chain reaction could be controlled, one would have
a tremendous source of power. Scientists began to speculate on the potential of
nuclear power plants. But if the chain reaction were to occur in a violent,
uncontrolled manner, one would have an atomic bomb. Scientists also began to
worry about the potential for nuclear weapons. It is interesting to note that
the science fiction writer H. G. Wells had written about the potential of
nuclear power in "The World Set Free", published in 1914.
One scientist,
Leo Szilard, began to worry about the potential for nuclear weapons in
the face of the growing hostility of Germany and the likelihood of massive,
technically based warfare. Szilard,
the Hungarian expatriate physicist, deduced that the discovery of fission
would lead either Germany or the Allies to high energy weapons. He
sought an audience with President Franklin Roosevelt but he was
rebuffed. But Szilard got assurance that a letter from Einstein would
be delivered to Roosevelt. Szilard went to Einstein, who prepared the
letter shown below. |
One
final question remained concerning the fission of uranium. In 1935, Arthur
Dempster, a Canadian-born chemist working at the University of Chicago, used a
mass spectrometer to find a heretofore unknown isotope of mass 235 hidden in
natural uranium, the overall mass of which was approximately 238. Three years
later, Alfred Nier used a mass spectrometer to measure the ratio of U-235 to
U-238 in natural uranium as 1:139, which meant that U-235 was present to the
extent of 0.7%.
Meanwhile,
at Princeton University, Niels Bohr and John Wheeler theorized that U-238 only
underwent fission with fast, high-energy neutrons, while slow, thermal neutrons
would produce fission only in U-235. John Dunning, a physicist working with
Fermi at Columbia University, decided to test the Bohr-Wheeler theory and made
a deal with Nier to obtain a few micrograms of pure U-235. Using this small
sample, Dunning’s group proved the Bohr-Wheeler hypothesis. Until this
discovery, the lighter isotope was not considered of importance in nuclear
reactions because of its low concentration. Now, to make a uranium bomb, it
would be necessary to separate U-235 from U-238, which is a difficult task.
Physical, not chemical, methods have to be used for the separation, since the
two isotopes have identical chemical properties.
The Discovery and Isolation of
Plutonium
The cyclotron at the University of California, Berkeley |
The transuranium element, plutonium, was the first synthetic
element to be produced on a large scale. In addition to being fissionable, it has interesting
and unusual chemical and metallurgical properties. The story of its discovery
and isolation is among the most fascinating in the history of science. The distinction
between discovery and isolation is significant. Discovery refers to the first
nuclear and chemical proof of the existence of atoms of a new element, while isolation is the procurement of
the first weighable amount in pure form. There was often a considerable
amount of time between the discovery and isolation of the transuranium
elements. |
The search for transuranium
elements initiated by Fermi continued unabated. In the spring of 1940, Edward
McMillan and Philip Abelson, working at the University of California Berkeley
(UCB), exposed a natural uranium target to 12 Mev neutrons produced by bombarding Be with cyclotron-accelerated deuterons (2H1).
238U92 +
1n0 --> 239U92 + g
239U92
t ˝ = 23.5 min.--> 239Np93 + b -
McMillan and Abelson were able to
prove that the chemical and nuclear properties of the product of the U-239 beta
decay were unique and thus discovered the first transuranium element, atomic
number 93. It was named neptunium (Np) after Neptune, the planet immediately
beyond Uranus. However, the first isolation of Np did not occur until October
1944.
(Courtesy of the University of California, Berkeley)
In
the summer of 1940, Glen Seaborg, Arthur Wahl, and Joseph Kennedy, a group of
chemists at UCB, began a search for the next transuranium element, 94, which
they thought to be a decay product (daughter) of Np-239.
239Np93
t ˝ = 2.3 days -1ß - --> 239?94
Continuing
the search for element 94 in the winter of 1941, they bombarded uranium oxide
with 16 Mev deuterons from the Berkeley cyclotron. They chemically identified
another isotope of neptunium, Np-238, which decayed by beta emission to an
isotope of element 94 (plutonium) that then emitted alpha particles.
238U92 +
2H1 --> 238Np93 + 21n0
238Np93
t 1/2 = 2.12 days --> 238Pu94 +
b -
238Pu94
t1/2 = 90 years --> a 2+ + 236U92
The Pu alpha particle emitter was
separated chemically from U, Np, and other reaction products and oxidized with potassium
peroxydisulfate, K2S2O8, to a fluoride-soluble
oxidation state. The other products of this neutron bombardment did not undergo
oxidation with K2S2O8 and thus
remained insoluble. The alpha activity (400 counts per minute) used to trace Pu
was concentrated in the resulting solution. The Pu in solution was then reduced to a lower oxidation state
with SO2 and precipitated as a fluoride using Ce3+ and La3+
as carriers. This chemistry, based on oxidation, reduction, and precipitation
reactions, would later prove the basis for the large-scale production of
plutonium. The alpha particle energy and activity was unique and thus indicated
a new element. At this time, Seaborg and Wahl could not identify which Pu
isotope produced the alpha activity. It was later identified as Pu-238.
Plutonium
solutions
(Courtesy of the University
of California, Berkeley)
Seaborg
remarked, "During this time, a great deal was learned about the chemistry
of plutonium. It was established that plutonium in its higher oxidation state
was not carried by lanthanum fluoride or cerium fluoride, in contrast to
plutonium in the lower state, which was quantitatively coprecipitated with
these compounds. The lower state could be oxidized to the higher state with
oxidizing agents such as persulfate, dichromate, permanganate, or periodate
ions, and then reduced by treatment with sulfur dioxide or bromide ion to the
lower oxidation state."
Later
in the spring of 1941, another more important isotope of plutonium, Pu-239, was
produced using neutrons from the Berkeley cyclotron to target a uranium
compound surrounded by paraffin. As Fermi’s group had discovered, the paraffin
acted as a moderator to slow the neutrons and thus increase the chances of
interaction with the target. This new Pu isotope, an alpha emitter with a half
life of about 24,000 years, was separated from other reaction products using
the same chemistry as that used to isolate Pu-238. However, the longer
half-life of Pu-239 reduced its activity, making it more difficult to detect
than Pu-238.
238U92 +
1n0 --> 239U92 + g
239U92 t
1/2 = 23.5 min. --> 239Np93 + b -
239Np93
t 1/2 = 2.35 days --> 239Pu94 + b -
239Pu93
t 1/2 = 24,110 yrs. --> 235U92 + a 2+
In March 1941, Seaborg’s group
irradiated a sample estimated to contain 0.25 mg of Pu-239 surrounded by
paraffin with neutrons produced in the cyclotron. Under these conditions, this
isotope appeared to undergo fission. When the Pu was replaced with a sample
containing approximately 0.5 mg U-235, the other known fissionable material,
neutron-induced fission was also observed, but at a rate approximately half
that of Pu-239. This discovery raised the possibility of using a controlled
chain reaction to produce quantities of Pu-239 sufficient for nuclear weapons.
The product Pu-239 would have to be separated from the unreacted uranium and
fission products by chemical means. It now became important to investigate the
chemistry of plutonium to develop large-scale separation procedures.
However,
in the summer of 1942, the cyclotron was the only means of producing plutonium,
and the amounts produced were so small that they could not be seen or weighed
with existing balances. Calculations showed that long periods of neutron
bombardment of uranium in the cyclotron would produce only a few micrograms of
Pu-239, much less than that normally required to determine the physical and
chemical properties of a new element. The preparation and measurement of such
small quantities of plutonium required the development of
"ultramicrochemical" techniques and equipment.
The
first weighing of a plutonium compound occurred in September of 1942, when 2.77
mg of PuO2 was placed on a balance especially designed for small
masses and calibrated with platinum wire. Liquid volumes in the range of 0.10
to 10-5 mL were delivered with an error of less than one percent
using calibrated capillary pipettes. Glassware, such as beakers and test tubes,
was made from capillary tubing and handled under a microscope with
micromanipulators. In November 1943, the first pure plutonium metal was
prepared by reducing 35 mg of PuF4 with barium metal at 1,400o
C. The plutonium metal appeared as silvery globules weighing about 3 mg each
and having an estimated density of 16 g/mL.
Although
the Pu-239 isotope had the potential to be fissionable material for bombs or
power generation, realization of this potential required larger amounts of this
isotope. Large-scale production of Pu-239 required a controlled nuclear chain
reaction of uranium, a feat that would soon be achieved by Enrico Fermi and Leo
Szilard in Chicago.
Chain
Reaction (December 2, 1942)
By
early 1942, it was known that the two naturally occurring isotopes of uranium
reacted with neutrons as follows:
235U92 + 1n0
--> fission products + (2.5)1n0 +
200 MeV Energy
238U92 + 1n0
--> 239U92
239U92
--> 239Np93 +
ß-1
t1/2=23.5 min.
239Np93
---> 239Pu94+
ß-1
t1/2=2.33 days
Each
U-235 that undergoes fission produces an average of 2.5 neutrons. In contrast,
some U-238 nuclei capture neutrons, become U-239, and subsequently emit two
beta particles to produce Pu-239. The times are half-lives for the successive beta emissions.
The first generations of a nuclear chain reaction
The
answers to two questions were critical to the production of plutonium for
atomic bombs. Is it possible, using natural uranium (99.3% U-238 and 0.7%
U-235), to achieve a controlled chain
reaction on a large scale? If so, some of the excess neutrons
produced by the fission of U-235 would be absorbed by U-238 and produce
fissionable Pu-239. The second question concerned how to separate (in a reasonable
period of time) the relatively small quantities of Pu-239 from the unreacted
uranium and the highly radioactive fission-product elements.
Although
fission had been observed on a small scale in many laboratories, noone had
carried out a controlled chain reaction. Fermi thought that he could achieve a
controlled chain reaction using natural uranium. He had started this work with
Leo Szilard at Columbia University, but moved to the University of Chicago in
early 1942. The nuclear reactor, called a pile, was composed of 80,590 lbs. of
uranium oxide, 12,400 lbs. of uranium, and 771,000 lbs. of ultrapure graphite
arranged in a manner to maximize neutron propagation. On December 2, 1942, the
first controlled nuclear chain reaction occurred in a squash court under the
football field at the University of Chicago. At around 2:20 p.m. the reactor
went critical; that
is, it produced one neutron for every neutron absorbed by the uranium nuclei.
Fermi allowed the reaction to continue for the next 27 minutes before inserting
neutron-absorbing cadmium control rods. In addition to excess neutrons and
energy, the pile also produced a small amount of Pu-239, the other known
fissionable material.
The
achievement of the first sustained nuclear reaction was the beginning of a new
age in nuclear physics and the study of the atom. Humankind could now use the
tremendous potential energy contained in the nucleus of the atom. However,
while a controlled chain reaction was achieved with natural uranium, it would
be necessary to separate U-235 from U-238 to build a uranium bomb. On December
28, 1942, upon reviewing a report from his advisors, President Roosevelt
recommended building full-scale plants to produce both U-235 and Pu-239. This
changed the effort to develop nuclear weapons from experimental work in
academic laboratories administered by the U.S. Office of Scientific Research
and Development to a huge effort by private industry. This work, supervised by
the U.S. Army Corps of Engineers, was codenamed the Manhattan Project. It
spread throughout the entire United States, with the facilities for uranium and
plutonium production being located at Oak Ridge, Tennessee, and Hanford,
Washington, respectively. Work on plutonium production continued at the
University of Chicago, at what became known as the Metallurgical Laboratory or
Met Lab. A new laboratory at Los Alamos, New Mexico, became the focal point for
development of the uranium and plutonium bombs.
-------------------------------
Plutonium
also exists in trace quantities in naturally occurring uranium ores. It is
formed in much the same manner as neptunium, by irradiation of natural uranium
with the neutrons which are present.
Plutonium has assumed the position of dominant
importance among the trasuranium elements because of its successful use as an
explosive ingredient in nuclear weapons and the place which it holds as a key
material in the development of industrial use of nuclear power. One kilogram is
equivalent to about 22 million kilowatt hours of heat energy. The complete
detonation of a kilogram of plutonium produces an explosion equal to about
20,000 tons of chemical explosive. Its importance depends on the nuclear
property of being readily fissionable with neutrons and its availability in
quantity. The world's nuclear-power reactors are now producing about 20,000 kg
of plutonium/yr. By 1982 it was estimated that about 300,000 kg had
accumulated. The various nuclear applications of plutonium are well known. 238Pu
has been used in the Apollo lunar missions to power seismic and other equipment
on the lunar surface. As with neptunium and uranium, plutonium metal can be
prepared by reduction of the trifluoride with alkaline-earth metals.
Plutonium creation
Plutonium is created when
non-fissionable uranium (U-238) absorbs a neutron released by the fission
process. In the first instance this produces uranium-239 which quickly sheds an
electron to turn into neptunium-239, rapidly followed by the loss of a further
electron which results in the creation of plutonium-239 (Pu-239), see figure 1.
Plutonium-239 is a fissile material so, as the chain reaction in a reactor
continues, some of the Pu-239 splits, releasing energy. Up to about half the
energy generated by a uranium-fuelled nuclear reactor is produced from
plutonium fission.
Not all of
the plutonium undergoes fission. A Pu-239 atom which has escaped fission may
absorb a second neutron and another isotope of plutonium, Pu-240, which has
different physical properties from Pu-239, is then produced. After some time, commonly about three
years, the reduction in fissionable uranium content and the accumulation of the
products of fission make the fuel unsuitable for continued use. Spent nuclear
fuel is replaced with new fuel, much as the spent battery in a torch is
replaced with a new one. The spent fuel still has great energy potential. In
addition to unused uranium, it contains Pu-239 which has not yet been
fissioned.
The most
important isotope of plutonium is Pu-239. It's virtually nonexistent in nature.
It is produced by bombarding uranium-238 with slow neutrons. This forms
neptunium-239, which in turn emits a beta particle and forms plutonium-239.
Plutonium-239's principal mode of decay is alpha decay. Various sources give
slightly different figures for the half-life. The values found include 24,360,
24,400, 24,110, and 24,000 years. None of theses measurements agree. It is
because there are many factors that can affect the accuracy of this
measurement. Plutonium-239 is produced artificially, and every time it is produced,
it is mixed with varying amounts of other isotopes, notably plutonium-240,
plutonium-241 and plutonium-242. Since all the isotopes have nearly the same
chemical characteristics, it is very difficult to separate isotopes from each
other by chemical techniques. This means, it is virtually impossible to study
the properties of pure Plutonium-239. Therefore, the results might be the
average half-life of it being mixed with a small amount of the other isotopes.
And there will be a slight difference in the density and purity of it every
time it is being produced, depending upon the amount of reactants used in the
process of its production. In addition, a little spontaneous fission occurs in
most plutonium isotopes. So while some of the Plutonium-239 atoms are undergoing
decay, a small number of them are splitting into less-massive nuclei. The rate
of fission is not a constant.
Plutonium-239 is one of the two
fissile materials used for the production of nuclear weapons and in some
nuclear reactors as a source of energy. The other fissile material is
uranium-235. Plutonium-239 is virtually nonexistent in nature. It is made by
bombarding uranium-238 with neutrons in a nuclear reactor. Uranium-238 is
present in quantity in most reactor fuel; hence plutonium-239 is continuously
made in these reactors. Since plutonium-239 can itself be split by neutrons to
release energy, plutonium-239 provides a portion of the energy generation in a
nuclear reactor.
The physical properties of plutonium metal are
summarized in Table 1.
TABLE 1. Physical Characteristics of Plutonium Metal
Color: |
Silver |
Melting point: |
641 deg. C |
Boiling point: |
3232 deg. C |
Density: |
16 to 20 grams/cubic centimeter |
Only two
plutonium isotopes have commercial and military applications. Plutonium-238,
which is made in nuclear reactors from neptunium-237, is used to make compact
thermoelectric generators; plutonium-239 is used for nuclear weapons and for
energy; plutonium-241, although fissile, (see next paragraph) is impractical
both as a nuclear fuel and a material for nuclear warheads. Some of the reasons
are far higher cost , shorter half-life, and higher radioactivity than
plutonium-239. Isotopes of plutonium with mass numbers 240 through 242 are made
along with plutonium-239 in nuclear reactors, but they are contaminants with no
commercial applications. I will focus on civilian and military plutonium (which
are interchangeable in practice--see Table 5), which consist mainly of
plutonium-239 mixed with varying amounts of other isotopes, notably
plutonium-240, -241, and -242.
Plutonium-239
and plutonium-241 are fissile materials. This means that they can be split by
both slow (ideally zero-energy) and fast neutrons into two new nuclei (with the
concomitant release of energy) and more neutrons. Each fission of plutonium-239
resulting from a slow neutron absorption results in the production of a little
more than two neutrons on the average. If at least one of these neutrons, on
average, splits another plutonium nucleus, a sustained chain reaction is
achieved.
The even
isotopes, plutonium-238, -240, and -242 are not fissile but yet aare
fissionable--that is, they can only be split by high energy neutrons.
Generally, fissionable but non-fissile isotopes cannot sustain chain reactions;
plutonium-240 is an exception to that rule.
The
minimum amount of material necessary to sustain a chain reaction is called the
critical mass. A supercritical mass is bigger than a critical mass, and is
capable of achieving a growing chain reaction where the amount of energy
released increases with time. The
amount of material necessary to achieve a critical mass depends on the geometry
and the density of the material, among other factors. The critical mass of a
bare sphere of plutonium-239 metal is about 10 kilograms. It can be
considerably lowered in various ways.
The amount of plutonium used in fission weapons is in the 3 to 5
kilograms range. Nuclear weapons with a
destructive power of 1 kiloton can be built with as little as 1 kilogram of
weapon grade plutonium. The smallest theoretical critical mass of plutonium-239
is only a few hundred grams.
In
contrast to nuclear weapons, nuclear reactors are designed to release energy in
a sustained fashion over a long period of time. This means that the chain
reaction must be controlled--that is, the number of neutrons produced needs to
equal the number of neutrons absorbed. This balance is achieved by ensuring
that each fission produces exactly one other fission.
All
isotopes of plutonium are radioactive, but they have widely varying half-lives.
The half-life is the time it takes for half the atoms of an element to decay.
For instance, plutonium-239 has a half-life of 24, 110 years while plutonium-241
has a half-life of 14.4 years. The various isotopes also have different
principal decay modes. The isotopes present in commercial or military
plutonium-239 are plutonium-240, -241, and -242. Table 2 shows a summary of the
radiological properties of five plutonium isotopes.
The
isotopes of plutonium that are relevant to the nuclear and commercial
industries decay by the emission of alpha particles, beta particles, or spontaneous fission. Gamma radiation,
which is penetrating electromagnetic radiation, is often associated with alpha and beta decays.
TABLE 2. Radiological Properties of Important Plutonium Isotopes
|
Pu-238 |
Pu-239 |
Pu-240 |
Pu-241 |
Pu-242 |
Half-life(in years) |
87.74 |
24,110 |
6537 |
14.4 |
376,000 |
Specific activity(curies/gram) |
17.3 |
.063 |
.23 |
104 |
.004 |
Principal decay mode |
alpha |
alpha |
alpha |
Beta |
Alpha |
Decay energy(MeV) |
5.593 |
5.244 |
5.255 |
.021 |
4.983 |
Radiological hazards |
alpha, weak gamma |
alpha, weak gamma |
alpha, weak gamma |
beta, weak gamma(b) |
alpha, weak gamma |
a) Source of neutrons causing added radiation dose to workers in nuclear
facilities. A little spontaneous fission occurs in most plutonium isotopes.
b) Plutonium-241 decays into Americium-241, which is an intense gamma-emitter.
Half-Life of Plutonium
During radioactive
decay, the time in which the strength of a radioactive source decays to
half its original value. In theory, the decay process is never complete and
there is always some residual radioactivity. For this reason, the half-life of
a radioactive isotope is measured, rather than the total decay time. It may
vary from millionths of a second to billions of years.
Radioactive
substances decay exponentially; thus the time taken for the first 50% of the
isotope to decay will be the same as the time taken by the next 25%, and by the
12.5% after that, and so on.
For example, carbon-14 takes about
5,730 years for half the material to decay; another 5,730 for half of the
remaining half to decay; then 5,730 years for half of that remaining half to
decay, and so on. Plutonium-239, one of the most toxic of all radioactive
substances, has a half-life of about 24,000 years.
------------------------------------------------------------------------------------
by E.
RUTHERFORD, M.A., B.SC.,
Macdonald Professor of Physics, McGill University, Montreal
From the
Philosophical Magazine for January 1900, ser. 5, xlix, pp. 1-14
Communicated by Professor J. J. Thomson, F.R.S.
Note: the page numbering is take
from "The Collected Works of Lord Rutherford of Nelson," vol. I
220
It has been shown by Schmidt* that
thorium compounds give out a type of radiation similar in its photographic and
electrical actions to uranium and Röntgen radiation. In addition to this
ordinary radiation, I have found that thorium compounds continuously emit
radioactive particles of some kind, which retain their radioactive powers for
several minutes. This 'emanation', as it will be termed for shortness, has the
power of ionizing the gas in its neighbourhood and of passing through thin
layers of metals, and, with great ease, through considerable thicknesses of
paper.
In order to make clear the
evidence of the existence of a radioactive emanation, an account will first be
given of the anomalous behaviour of thorium compounds compared with those of uranium.
Thorium oxide has been employed in most of the experiments, as it exhibits the
'emanation' property to a greater degree than the other compounds; but what is
true for the oxide is also true, but to a less extent, of the other thorium
compounds examined, viz. the nitrate, sulphate, acetate, and oxalate.
In a previous paper** the author
has shown that the radiation from thorium is of a more penetrating character
than the radiation from uranium. Attention was also directed to the inconstancy
of thorium as a source of radiation. Owens*** has investigated in more detail
the radiation from thorium compounds. He has shown that the radiations from the
different compounds are of the same kind, and, with the exception of thorium
oxide in thick layers, approximately homogeneous in character.
The intensity of thoriurn
radiation, when examined by means of the electrical discharge produced, is
found to be very variable; and this inconstancy is due to slow currents of air
produced in an open room. When the apparatus is placed in a closed vessel, to
do away with air currcnts, the intensity is found to be practically constant.
The sensitiveness of thorium oxide to
221
slight currents of air is very
remarkable. The movement of the air caused by the opening or closing of a door
at the end of the room opposite to where the apparatus is placed, is often
sufficient to considerably diminish the rate of discharge. In this respect
thorium compounds differ from those of uranium, which are not appreciably
affected by slight currents of air. Another anomaly that thorium compounds
exhibit is the ease with which the radiation apparently passes through paper.
The following table is an example of the way the rate of leak between two
parallel plates, one of which is covered with a thick layer of thorium oxide,
varies with the number of layers of ordinary foolscap paper placed over the
radioactive substance.
TABLE I |
|
Thickness
of each Layer of Paper = 0.008 cm. 50 volts between plates |
|
Number
of Layers of |
Rate of
Disharge |
0 |
1 |
1 |
0.74 |
2 |
0.74 |
5 |
0.72 |
10 |
0.67 |
20 |
0.55 |
In the above table the rate of
leak with the thorium oxide uncovered is taken as unity. It will be observed
that the first layer reduced the rate of leak to 0.74, and the five succeeding
layers produce very little effect. The action, however, is quite different if
we use a thin* layer of thorium
oxide. With one layer of paper, the rate of discharge is then reduced to less
than 1/16 of its value. At first sight it appears as if the thorium oxide gave
out two types of radiation, one of which is readily absorbed by paper, and the
other to only a slight extent. If we examine the radiation given out by
TABLE II
|
|
Thickness
of Paper = 0.0027 cm. |
|
Number
of Layers of Thin Paper |
Rate of
Discharge |
0 |
1 |
1 |
0.37 |
2 |
0.16 |
3 |
0.08 |
* To produce a thin layer on a plate, the oxide, in the
form of a fine powder, was sprinkled by means of a fine gauze, so as to cover
the plate to a very small depth. By a thick layer is meant a layer of oxide
over a millimetre in thickness.
222
a thin layer of thorium oxide, by
placing successive layers of thin paper upon it, we find the radiation is
approximately homogeneous, as the Table II (p. 221) shows.
The rate of leak of the bare salt
is taken as unity. If the radiation is of one kind, we should expect the rate
of discharge (which is proportional to the intensity of the radiation) to
diminish in geometrical progression with the addition of equal thicknesses of
paper. The above figures show that this is approximately the case. With a thick
layer of thorium oxide, by adding successive layers of thin paper, we find the
rate of discharge gradually diminish, till after a few layers it reaches a
constant value. The amount that is cut off by the first layer of foolscap paper
(see Table I) is of the same kind of radiation as that which is emitted by a
thin layer of oxide.
On directing a slight current of
air between the test plates, the rate of discharge due to a thick layer of
thorium oxide is greatly diminished. The amount of diminution is to a great
extent independent of the electromotive force acting between the plates. Under
similar conditions with uranium, the rate of leak is not appreciably affected.
With a thin layer of oxide, the diminution of the rate of leak is small; but
with a thick layer of oxide, the rate of leak may be reduced to less than
one-third of its previous value. If two thicknesses of foolscap paper are
placed over the thorium oxide, the resulting rate of leak between the plates
may be diminished to less than 1/10 of its value by a slight continuous blast
of air from a gasometer or bellows.
The phenomena exhibited by thorium
compounds receive a complete explanation if we suppose that, in addition to the
ordinary radiation, a large number of radioactive particles are given out from
the mass of the active substance. This 'emanation' can pass through
considerable thicknesses of paper. The radioactive particles emitted by the
thorium compounds gradually diffuse through the gas in its neighbourhood and
become centres of ionization throughout the gas. The fact that the effect of
air currents is only observed to a slight extent with thin layers of thorium
oxide is due to the preponderance, in that case, of the rate of leak due to the
ordinary radiation over that due to the emanation. With a thick layer of
thorium oxide, the rate of leak due to the ordinary radiation is practically
that due to a thin surface layer, as the radiation can only penetrate a short
distance through the salt. On the other hand, the 'emanation' is able to
diffuse from a distance of several millimetres below the surface of the
compound, and the rate of leak due to it becomes much greater than that due to
the radiation alone.
The explanation of the action of
slight currents of air is clear on the 'emanation' theory. Since the
radioactive particles are not affected by an electrical field, extremely minute
motions of air, if continuous, remove many of the radioactive centres from
between the plates. It will be shown shortly that the emanation continues to
ionize the gas in its neighbourhood for several minutes, so that the removal of
the particles from between the plates diminishes the rate of discharge between
the plates.
223
Duration of the Radioactivity of the Emanation
The emanation gradually loses its
radioactive power. The following method was adopted to determine the rate of
decay of the intensity of the radiation of the radioactive particles emitted by
thorium oxide. A thick layer of thorium oxide was enclosed in a narrow rectangular
paper vessel A (Fig. 1), made up of two thicknesses of foolscap paper. The
paper cut off the regular radiation almost entirely, but allowed the emanation
to pass through. The thorium thus enclosed was placed inside a long metal tube
B.
One end of the tube was connected
to a large insulated cylindrical vessel C, which had a number of small holes in
the end for the passage of air. Inside C was fixed an insulated electrode, D,
connected with one pair of quadrants of a Thomson electrometer. The cylinder,
C, was connected to one terminal of a battery of 100 volts, the other terminal
of which was connected to earth.
A slow current of air from an
aspirator or gasometer, which had been freed from dust by its passage through a
plug of cotton-wool, was passed through the apparatus. The current of air, in
its passage by the thorium oxide, carried away the radioactive particles with
it, and these were gradually conveyed into the large cylinder C. The
electrometer needle showed no sign of movement until the radioactive particles
were carried into C. In consequence of the ionization of the gas in the
cylinder by the radioactive particles, a current passed between the electrodes
C and D. The value of the current was the same whether C was connected with the
positive or negative pole of the battery. When the current of air had been
flowing for some minutes, the current between C and D reached a constant value.
The flow of air was then stopped, and the rate of leak between C and D observed
at regular intervals. It was found that the current between C and D persisted
for over ten minutes.
224
The following is a series of
observations.
TABLE
III |
|
Time in
seconds |
Current |
0 |
1 |
28 |
0.69 |
62 |
0.51 |
118 |
0.23 |
155 |
0.14 |
210 |
0.067 |
272 |
0.041 |
360 |
0.018 |
Fig. 2, curve A, shows the
relation existing between the current through the gas and the time. The
current, just before the flow of air is stopped, is taken as unity. It will be
observed that the current through the gas diminishes in a geometrical progression
with the time. It can easily be shown, by the theory of ionization, that the
current through the gas is proportional to the intensity of the radiation
emitted by the radioactive particles. We therefore see that the intensity of
the radiation given out by the radioactive particles falls off in a geometrical
progression with the time. The result shows that the intensity of the radiation
has fallen to one-half its value after an interval of about one
225
minute. The rate
of leak due to the emanation was too small for measurement after an interval of
ten minutes.
If the ionized gas had been
produced from a uranium compound, the duration of the conductivity, for
voltages such as were used, would only have been a fraction of a second.
The rate of decay of intensity is
independent of the electromotive force acting on the gas. This shows that the
radioactive particles are not destroyed by the electric field. The current
through the gas at any particular instant, after stoppage of the flow of air,
was found to be the same whether the electromotive force had been acting the
whole time or just applied for the time of the test.
The current through the gas in the
cylinder depends on the electromotive force in the same way as the current
through a gas made conducting by Röntgen rays. The current at first increases
nearly in proportion to the electromotive force, but soon reaches an
approximate 'saturation' value.
The duration of the radioactivity
was also tested by another method. The paper vessel containing the thorium
oxide was placed inside a long brass cylinder over 200 cm. in length. A slow
current of air (with a velocity of about 2 cm. per sec. along the tube) was
passed over the thorium oxide along the tube, and then between two insulated
concentric cylinders. The rate of leak between the two concentric cylinders
(potential difference 270 volts) was observed when the air had been passing
sufficiently long to produce a steady state. The rates of leak were observed
for varying positions of the thorium oxide along the tube. Knowing the velocity
of the current of air along the tube, the time taken to carry the radioactive
particles to the testing apparatus could be determined. In this way it was
found that the rate of decay was about the same as determined by the first
method, i.e. the intensity fell to half its value in about one minute.
In this apparatus experiments were
also tried to see whether the radioactive particles moved in an electric field.
The experiments on the effect of a current of air on the rate of discharge
naturally suggest that possibly one of the ions was so large that it moved
extremely slowly even in strong electric fields. The results obtained showed
that the particles did not move with a greater velocity than 1/100,000 cm. per
sec. for a potential gradient of one volt per centimetre; and it is probable
that the partides do not move at all in an electric field. By blowing the
emanation into an inductor, no evidence of any charge in the emanation could be
detected. We may therefore conclude that the emanation is uncharged, and is not
appreciably affected by an electric field.
Properties of the Emanation
The emanation passes through a
plug of cotton-wool without any loss of its radioactive powers. It is also
unaffected by bubbling through hot or cold water, weak or strong sulphuric
acid. In this respect it acts like an ordinary gas.
226
An ion, on the other hand, is not
able to pass through a plug of cotton-wool, or to bubble through water, without
losing its charge.
The emanation is similar to
uranium in its photographic and electrical actions. It can ionize the gas in
its neighbourhood, and can affect a photographic plate in the dark after
several days' exposure. Russell* has shown that the active agent in producing
photographic action in the case of metals, paper, etc., is due to hydrogen
peroxide. Hydrogen peroxide apparently has the power of passing in some way
through considerable thicknesses of special substances, and in this respect the
emanation resembles it. Hydrogen peroxide, however, does not ionize the gas in
its neighbourhood. The action of hydrogen peroxide on the photographic plate is
purely a chemical one; but it is the radiation from the emanation, and not the
emanation itself, that produces ionizing and photographic actions.
The radioactive emanation passes
through all metals if sufficiently thin. In order to make certain that the
emanation passed through the material to be examined and did not diffuse round
the edges, the radioactive substance was placed in a square groove of a thick
lead plate. Two layers of paper were pasted tightly over the opening to cut off
the regular radiation. The material to be tested was then firmly waxed down on
the lead plate. The following numbers illustrate the effect of different metals.
The rate of discharge, due to the emanation between two parallel plates 4 cm.
apart, was observed.
Aluminium
Foil, thickness = 0.0008 cm. |
|
Number
of Layers |
Rate of
Discharge |
0 |
1 |
1 |
0.66 |
3 |
0.42 |
6 |
0.16 |
Cardboard,
thickness 0.08 cm. |
|
Layers |
Rate of
Discharge |
0 |
1 |
1 |
0.40 |
2 |
0.21 |
The emanation passed readily
through several thicknesses of gold- and silver-leaf. A plate of mica,
thickness 0.006 cm., was completely impervious to the emanation.
When a thick layer of thorium
oxide, covered over with several thicknesses of paper, is placed inside a
closed vessel, the rate of discharge due to the emanation is small at first,
bue gradually increases, until after a few minutes a steady state is reached.
* Proc. Roy. Soc., 1897.
227
These results are to be expected,
for the emanation can only slowly diffuse through the paper and the surrounding
air. A steady state is reached when the rate of loss of intensity due to the
gradual decay of the radioactivity of the emanation is recompensed by the
number of new radioactive centres supplied from the thorium compound.
Let n = number of ions produced per second by the
radioactive particles between the plates.
Let q = number of ions supplied per second by the emanation diffusing from the
thorium.
The rate of variation of the
number of ions at any time t is given by
dn / dt =
q - ln
where l is a constant.
The results given in Table III
show that the rate of diminution of the number of ions is proportional to the
number present.
Solving the equation, it is seen
that
loge
(q - ln) = - lt + A
where A is a constant.
When
t = 0, n =
0
therefore
A = loge
q
Thus
n = (q /
l) (1 - eŻlt)
With a large potential difference
between the test plates the current i through the gas at any time is given by
i = ne
where e is the charge on an ion.
When a steady state is reached, dn
/ dt = 0; and the maximum number N of ions produced per second by the
radioactive particles between the plates is given by
N = q / l
and the maximum current I is given
by
I = Ne
Therefore
i / I = 1
- eŻlt
228
The current thus increases
according to the same law as a current of electricity rises in a circuit of
constant inductance.
This result is confirmed by an
experiment on the rise of the current between two concentric cylinders. The
thorium oxide enclosed in paper was placed inside the cylinder. A current of
air was sent between the cylinders in order to remove the emanation as rapidly
as it was formed. The current of air was then stopped and the current between
the two cylinders observed, by means of an electrometer, for successive
intervals after the current of air ceased. Table IV gives the results obtained.
TABLE IV |
|
Time in
seconds |
Current
in Scale Divisions |
0 |
2.4 |
7.5 |
3.3 |
2.3* |
6.5 |
4.0 |
10.0 |
5.3 |
12.5 |
6.7 |
13.8 |
9.6 |
17.1 |
12.5 |
19.4 |
18.4 |
22.7 |
24.4 |
25.3 |
30.4 |
25.6 |
48.4 |
25.6 |
The results are expressed in Fig.
2, curve B, where the ordinate represents current and the abscissa time. It
will be observed that the curve of rise of the current is similar in form to
the rise of an electric current in a circuit of constant inductance. The current
reaches half its value about one minute after the current of air has stopped-a
result which agrees with the equation given, for eŻlt = 1/2
when t = 60 sec. (see Table IV). At the instant of stopping the current of air
the current has a definite value, since most of the ions given off by the
emanation, before it is blown out of the cylinders, reach the electrodes. When
the source of the emanation is removed, q = 0, and the decay of the number of
ions produced by the emanation is given by the equation
dn / dt = Żln
* Editor's Footnote: - This and the following figures
in the same column should read: 23, 40, 53, etc. This, and similar minor
errors, left as in original.
229
If n = N when t = 0, it is easily
seen that
n / N = eŻlt
or
i / I = eŻlt
i.e. the current through the gas
diminishes in a geometrical progression. After 20 minutes the current through
the gas is only about one millionth part of its initial value. It has been
shown that eŻlt = 1/2
when t = 60 sec.
Therefore
l = 1 / 86
and
N = q / l
= 86q
or the total number of ions
produced per second when a steady state is reached is 86 times the number of
ions supplied per second by the emanation.
The amount of emanation from
thorium oxide increases with the thickness of the layer. When 1 gramme of
thorium oxide was spread over a surface of 25 cm.2, the amount of
discharge due to the ordinary radiation had practically reached a maximum. The
rate of leak due to the emanation for the same thickness was small. With 9
grammes of oxide spread over the same area, the rate of leak due to the
emanation had reached about half its maximum value, which for that case
corresponded to four times the rate of leak caused by the ordinary radiation.
The emanation thus still preserves its radioactive properties after diffusing
through several millimetres of thorium compound.
The emanation is given out
whatever the gas by which the thorium is surrounded. The action is very similar
whether air, oxygen, hydrogen, or carbonic acid is used.
The rate of discharge due to the
emanation diminishes with lowering of the pressure of the air surrounding it.
Only a few observations have been made, but the results seem to point to a
uniform rate of emission of the emanation at all pressures; but since the
intensity of the ionization of the gas varies directly as the pressure, the
rate of leak decreases with lowering of the pressure.
The amount of the emanation, so
far as the experiments have gone, is also independent of the quantity of
water-vapour present.
The power of emitting radioactive
particles is not possessed to any appreciable extent by other radioactive
substances besides thorium. All the compounds of thorium examined possess it to
a marked degree, and it is especially large in the oxide. Two different
specimens of the oxide have been used, one obtained from Schuchart of Germany,
and the other from Eimer and Amend of New York. The oxide is prepared by the
latter by igniting thorium nitrate obtained from monazite sand.
230
The amount of discharge caused by
the emanation is increased several times by the conversion of the nitrate into
the oxide; but at the same time, the rate of discharge due to the ordinary
radiation emitted by the thorium is increased in about an equal ratio. The
conversion of the nitrate into the oxide took place below a red heat. On
heating in a muffle for some time at white heat, the amount of emanation
continually diminished, till after four hours' exposure to the heat, the rate
of discharge due to the emanation was only of the value immediately after its
conversion into oxide.
Both thorium oxalate and sulphate
act in a similar manner to the nitrate; but the emanation is still given off to
a considerable extent after continued heating.
In considering the question of the
origin and nature of the emanation, two possible explanations naturally suggest
themselves, viz.:
(1) That the emanation may be due
to fine dust particles of the radioactive substance emitted by the thorium
compounds.
(2) That the emanation may be a
vapour given off from thorium compounds.
The fact that the emanation can
pass through metals and large thicknesses of paper and through plugs of
cotton-wool, is strong evidence against the dust hypothesis. Special
experiments, however, were tried to settle the question. The experiments of
Aitken and Wilson* have shown that ordinary air can be completely freed from
dust particles by repeated small expansions of the air over a water surface.
The dust particles act as nuclei for the formation of small drops, and are
removed from the gas by the action of gravity.
The experiment was repeated with
thorium oxide present in the vessel. The oxide was enclosed in a paper
cylinder, which allowed the emanation to pass through it. After repeated
expansions no cloud was formed, showing that for the expansions used the
particles of the emanation were too small to become centres of condensation of
the water-vapour. We may therefore conclude, from this experiment, that the
emanation does not consist of dust particles of thorium oxide.
It would be of interest to examine
the behaviour of the emanation for greater and more sudden expansions, after
the manner employed by C. T. R. Wilson** in his experiments on the action of
ions as centres of condensation.
The emanation may possibly be a
vapour of thorium. There is reason to believe that all metals and substances
give off vapour to some degree. If the radioactive power of thorium is
possessed by the molecules of the substance, it would be expected that the
vapour of the substance would be itself radioactive for a short time, but the
radioactive power would diminish in consequence of the rapid radiation of
energy. Some information on this point could probably be obtained by
observation of the rate of diffusion of the emanation into gases. It is hoped that
experimental data of this kind will lead to an approximate determination of the
molecular weight of the emanation.
* Trans. Roy. Soc., 1897.
** Phil. Trans. Roy. Soc., clxxxix, 1897.
231
Experiments have been tried to see
if the amount of the emanation from thorium oxide is sufficient to appreciably
alter the pressure of the gas in an exhausted tube. The oxide was placed in a
bulb connected with a Plücker spectroscopic tube. The whole was exhausted, and
the pressure noted by a McLeod gauge. The bulb of thorium oxide was
disconnected from the main tube by means of a stopcock. The Plücker tube was
refilled and exhausted again to the same pressure. On connecting the two tubes
together again, no appreciable difference in the pressure or in the appearance
of the discharge from an induction coil was observed. The spectrum of the gas
was unchanged.
Experiments, which are still in
progress, show that the emanation possesses a very remarkable property. I have
found that the positive ion produced in a gas by the emanation possesses the
power of producing radioactivity in all substances on which it falls. This
power of giving forth a radiation lasts for several days. The radiation is of a
more penetrating character than that given out by thorium or uranium. The
emanation from thorium compounds thus has properties which the thorium itself
does not possess. A more complete account of the results obtained is reserved
for a later communication.
McGill University, Montreal
September 13, 1899
-------------------------------------------------------------------------------------------------------------------------------
Half-Life
of Plutonium-239
The
half life of plutonium-239 is 24,110 years.
Of
an original mass of 100 g, how much remains
after
96,440 years?
˝ life = 24,110 yrs
96440 yrs x 1 half life = 4 half lives
24110 yrs
100 g ŕ 50 g ŕ 25 g ŕ 12.5 g ŕ 6.25 g
1
half-life 2 half-lives 3 half-lives 4
half-lives
6.25 g remain after 96,440 yrs.
Table 3
describes the chemical properties of plutonium in air. These properties are
important because they affect the safety of storage and of operation during
processing of plutonium. The oxidation of plutonium represents a health hazard
since the resulting stable compound, plutonium dioxide is in particulate form
that can be easily inhaled. It tends to stay in the lungs for long periods, and
is also transported to other parts of the body. Ingestion of plutonium is
considerably less dangerous since very little is absorbed while the rest passes
through the digestive system.
TABLE 3. How Plutonium Metal Reacts in Air
Forms
and Ambient Conditions: |
Reaction: |
Non-divided metal at room temperature (corrodes) |
relatively inert, slowly oxidizes |
Divided metal at room temperature (PuO2) |
readily reacts to form plutonium dioxide |
Finely divided particles under about particles over about |
spontaneously ignites at about
150 C spontaneously ignites at about
500 C. |
Humid, elevated temperatures (PuO2) |
readily reacts to form plutonium dioxide |
Plutonium
combines with oxygen, carbon, and fluorine to form compounds which are used in
the nuclear industry, either directly or as intermediates. Table 4 shows some important plutonium
compounds. Plutonium metal is insoluble in nitric acid and plutonium is
slightly soluble in hot, concentrated nitric acid. However, when plutonium
dioxide and uranium dioxide form a solid mixture, as in spent fuel from nuclear
reactors, then the solubility of plutonium dioxide in nitric acid is enhanced
due to the fact that uranium dioxide is soluble in nitric acid. This property
is used when reprocessing
irradiated nuclear fuels.
TABLE 4. Important Plutonium Compounds and Their Uses
Compound: |
Use: |
Oxides |
can be mixed with uranium dioxide (UO2) for use as reactor
fuel |
Carbides |
all three carbides can
potentially be used as fuel in breeder reactors |
Fluorides |
both fluorides are intermediate
compounds in the production of plutonium metal |
Nitrates |
no use, but it is a product of
reprocessing (extraction of plutonium from used nuclear fuel). |
Plutonium-239
is formed in both civilian and military reactors from uranium-238.
The
subsequent absorption of a neutron by plutonium-239 results in the formation of
plutonium-240. Absorption of another neutron by plutonium-240 yields
plutonium-241. The higher isotopes are formed in the same way. Since
plutonium-239 is the first in a string of plutonium isotopes created from
uranium-238 in a reactor, the longer a sample of uranium-238 is irradiated, the
greater the percentage of heavier isotopes. Plutonium must be chemically
separated from the fission products and remaining uranium in the irradiated
reactor fuel. This chemical separation is called reprocessing.
Fuel in
power reactors is irradiated for longer periods at higher power levels, called
high "burn-up", because it is fuel irradiation that generates the
heat required for power production. If the goal is production of plutonium for
military purposes then the "burn-up" is kept low so that the
plutonium-239 produced is as pure as possible, that is, the formation of the
higher isotopes, particularly plutonium-240, is kept to a minimum.
Plutonium
has been classified into grades by the Department of Energy (DOE) as depicted
in Table 5.
It is
important to remember that this classification of plutonium according to grades
is somewhat arbitrary. For example, although "fuel grade" and
"reactor grade" are less suitable as weapons material than
"weapon grade" plutonium, they can also be made into a nuclear
weapon, although the yields are less predictable because of unwanted neutrons
from spontaneous fission. The ability of countries to build nuclear arsenals
from reactor grade plutonium is not just a theoretical construct. In 1962 the United States conducted a
successful test with "reactor grade" plutonium. All grades of
plutonium can be used as weapons of radiological warfare which involve weapons
that disperse radioactivity without a nuclear explosion.
TABLE 5. Grades of Plutonium
Grades |
Pu-240 Content |
Supergrade |
2-3 % |
Weapon grade |
< 7 % |
Fuel grade |
7-19 % |
Reactor grade |
19 % or greater |
Isotopes
Plutonium
has 16 known isotopes (Pu-238 was discovered in 1992), with mass numbers
ranging from 232 to 246. All isotopes
of plutonium are radioactive, but they have widely varying half-lives. The
half-life is the time it takes for half the atoms of an element to decay. The
various isotopes also have different principal decay modes.
Isotopes of
Plutonium
Click on
an isotope to get more information about its decay |
|||
4 ms |
0+ |
%A=100 |
|
|
|
%A=? |
|
|
0+ |
%A=? |
|
|
|
|
|
34.1 m |
0+ |
%EC=77 6, %A=23 6 |
|
20.9 m |
|
%EC+%B+=99.88 5, %A=0.12 5 |
|
8.8 h |
0+ |
%EC ~ 94, %A ~ 6 |
|
3 ns |
|
|
|
25.3 m |
(5/2+) |
%EC+%B+=99.9973 5, %A=0.0027 5 |
|
25 ns |
|
|
|
2.858 y |
0+ |
%A=100, %SF=1.37E-7 7 |
|
37 ps |
(0+) |
|
|
34 ns |
|
|
|
45.2 d |
7/2- |
%A=0.0042 4, %EC=99.9958 4 |
|
0.18 s |
1/2+ |
%IT=100 |
|
85 ns |
|
|
|
1.1 us |
|
|
|
87.7 y |
0+ |
%A=100, %SF=1.85E-7 4, %MG ~ 6E-15, %SI ~ 1.4E-14 |
|
0.6 ns |
|
|
|
6.0 ns |
(0+) |
|
|
24110 y |
1/2+ |
%A=100, %SF=3.0E-10 8 |
|
7.5 us |
(5/2+) |
|
|
2.6 ns |
(9/2-) |
|
|
6563 y |
0+ |
%A=100 , %SF=5.75E-6 5 |
|
14.35 y |
5/2+ |
%B-=99.998, %A=0.00245 2, %SF ~ 2.4E-14 |
|
21 us |
|
|
|
32 ns |
|
|
|
3.733e+5 y |
0+ |
%A=100 , %SF=5.54E-4 6 |
|
4.956 h |
7/2+ |
%B-=100 |
|
45 ns |
|
|
|
8.08e+7 y |
0+ |
%A=99.879 4, %SF=0.121 4, %BB < 3E-11 |
|
10.5 h |
(9/2-) |
%B-=100 |
|
90 ns |
|
|
|
10.84 d |
0+ |
%B-=100 |
|
2.27 d |
|
%B-=100 |
By far of greatest importance is the isotope 239Pu,
with a half-life of 24,100 years, produced in extensive quantities in nuclear
reactors from natural uranium: 238U(n, gamma) --> 239U--(beta)
--> 239Np--(beta) --> <239Pu.
Plutonium also exhibits four ionic valence states in
aqueous solutions: Pu+3 (blue lavender), Pu+4 (yellow
brown), PuO+ (pink?), and PuO+2 (pink-orange). The ion
PuO+ is unstable in aqueous solutions, disproportionating into Pu+4
and PuO+2. The Pu+4 thus formed, however, oxidizes the
PuO+ into PuO+2, itself being reduced to Pu+3,
giving finally Pu+3 and PuO+2. Plutonium forms binary compounds
with oxygen: PuO, PuO2, and intermediate oxides of variable
composition; with the halides: PuF3, PuF4, PuCl3,
PuBr3, PuI3; with carbon, nitrogen, and silicon: PuC,
PuN, PuSi2. Oxyhalides are also well known: PuOCl, PuOBr, PuOI.
Shown
as isotope, half-life, and natural abundance (if available).
228Pu 4 milliseconds
229Pu
230Pu
231Pu
232Pu 34.1
minutes
233Pu 20.9
minutes
234Pu 8.8 hours
234m1Pu 3 nanoseconds
235Pu 25.3
minutes
235m1Pu 25
nanoseconds
236Pu 2.858 years
236m1Pu 37
picoseconds
236m2Pu 34
nanoseconds
237Pu 45.2 days
237m1Pu 0.18 seconds
237m2Pu 85
nanoseconds
237m3Pu 1.1
microseconds
238Pu 87.7 years
238m1Pu 0.6
nanoseconds
238m2Pu 6.0
nanoseconds
239Pu 24110 years
239m1Pu 7.5
microseconds
239m2Pu 2.6
nanoseconds
240Pu 6563 years
241Pu 14.35 years
241m1Pu 21
microseconds
241m2Pu 32
nanoseconds
242Pu 3.733 X 105
years
243Pu 4.956 hours
243m1Pu 45
nanoseconds
244Pu 8.08 X 107
years
245Pu 10.5 hours
245m1Pu 90
nanoseconds
246Pu 10.84 days
247Pu 2.27 days
The plutonium isotopes listed
below are "fissionable," which means that the nuclei can be split
into two fragments, called fission products. In addition to being fissionable,
plutonium-239 and plutonium-241 are "fissile" - that is, they can be
split by neutrons of very low (ideally zero) energy. This means that they can
be assembled into a critical mass, and hence can sustain a chain reaction
without an external source of neutrons.
Important
Radiological Properties of Plutonium Isotopes |
|||||
|
Pu-238 |
Pu-239 |
Pu-240 |
Pu-241 |
Pu-242 |
Half-life
(in years) |
87.74 |
24,110 |
6,537 |
14.4 |
376,000 |
Specific
activity (curies/gram) |
17.3 |
0.063 |
0.23 |
104 |
0.004 |
Principal
decay mode |
Alpha |
alpha |
alpha
and some spontaneous fission1 |
beta |
alpha |
Decay
energy (MeV) |
5.593 |
5.244 |
5.255 |
0.021 |
4.983 |
Radiological
hazards |
alpha
and weak gamma |
alpha
and weak gamma |
alpha
and weak gamma |
beta and
weak gamma2 |
alpha
and weak gamma |
How
isotope is produced |
nuclear
reactors |
nuclear
reactors |
nuclear
reactors |
nuclear
reactors |
nuclear
reactors |
Main
uses |
Production
of thermoelectric power used in nuclear weapons, satallites, and heart
pacemakers |
Fissile
material for nuclear weapons, and for the production of energy |
none |
none |
none |
1Source of
neutrons causing added radiation dose to workers in nuclear facilities.
2Plutonium-241 decays into Americium-241, which is an intense gamma
emitter.
Properties
The metal has a silvery appearance and takes on a
yellow tarnish when slightly oxidized. It is chemically reactive. A relatively
large piece of plutonium is warm to the touch because of the energy given off
in alpha decay. Larger pieces will produce enough heat to boil water. The metal
readily dissolves in concentrated hydrochloric acid, hydroiodic acid, or
perchloric acid. The metal exhibits six allotropic modifications having various
crystalline structures. The densities of these vary from 16.00 to 19.86 g/cm3.
Plutonium is toxic if ingested but
the problems associated with the toxicity of plutonium are no different in type
from those presented by a whole range of industrial substances, such as heavy
metals. There are other substances found in nature which are more toxic than
plutonium, and there are many well known substances in everyday use which, like
plutonium, are very toxic if they are not handled properly.
Very
strict protection measures are taken at each stage of the handling process. For
ease of handling plutonium is generally kept in the form of one of its oxides,
which are virtually insoluble in bodily fluids and so essentially non-toxic.
Plutonium used in the manufacture of MOX fuel is in the form of solid pellets
made from oxide powder. In commercial
power plant or research applications, plutonium generally exists as the
compound plutonium dioxide (PuO2), a very
stable ceramic material which is extremely insoluble in water or body fluids,
reducing the chemical toxicity to negligible levels, unless inhaled.
Plutonium
is radioactive but the main type of radiation it emits (alpha particles) does
not penetrate even very thin layers of materials. This means that a pair of
gloves can protect against the radiation from plutonium. Precautions are taken
in the handling of plutonium in order to prevent harm to the work force and to
the general public. These have proved effective for more than 30 years.
|
U-235 captures slow neutrons much more frequently than
fast neutrons. Fission produces fast neutrons. These lose energy in bouncing
against moderator nuclei and emerge as slow neutrons to split more U-235
nuclei. |
----------------------------------------------------------------------------------
Plutonium in Nuclear Explosives
Plutonium-239
is a fissile material well-known for its use as the primary trigger in most
nuclear explosives (Figure 1-1). All grades of plutonium (see Table 2-1) are
considered useable in nuclear explosives, but weapon-grade plutonium--which
contains more than 92% plutonium-239--is preferred for nuclear weapon arsenals
because lower amounts of plutonium-239 found in fuel and reactor grade pose a
much higher risk of “pre-initiation” of the trigger due to corresponding higher
amounts of plutonium-240. Use of lower grades also makes fabrication of the
plutonium trigger, or pit, more difficult.iii Because of its use in
weapons of mass destruction, plutonium accounting is conducted to the level of
grams, and large security forces are necessary to guard it.
However, the use of fuel or reactor grade plutonium is considered an easier
path for a nonweapons state or a terrorist group because: easiest way to make a
nuclear weapon is with reactor-grade plutonium because:
Figure 1-1. A simplified
illustration of how a precise detonation of chemical high explosives
surrounding a subcritical mass of fissile materials generates enough force to
initiate, or trigger, the nuclear detonation.
Plutonium
Chemical Complexity
If anything contributes to plutonium’s demise as a military tool it will be its
inherent chemical instability. The future of the plutonium triggers in the U.S.
nuclear weapons stockpile is the focus of intense debate both internally and
externally to the weapons labs and in the Pentagon. In particular, the lack of
understanding of how plutonium ages is driving calls for renewed large-scale
pit production. Lawrence Livermore National Laboratory spins it this way,
“predicting kinetics is crucial to avoiding surprise requirements for
large-scale refurbishment and remanufacture of weapons components.”v
Plutonium is cited by the nuclear
weapons labs as the most complex metal in the periodic table and continues to
baffle people who best understand it (see sidebar). U.S. and Russian weapons
scientists do not even agree on the “phase diagram” for the easily machinable
delta-phase plutonium that dominates nuclear weapons stockpiles.vi Its traits
are commonly described as unstable, unpredictable, anomalous, and dramatically
variable in the open literature. The litany of difficulties includes:
Figure
1-2. This diagram is commonly used to illustrate plutonium complexity, showing
the contrasts between the dramatic and abrupt six phase changes of plutonium as
it is heated compared to the stability of iron. Some of the key traits of the
different phrases include:
·
Alpha-phrase plutonium is brittle and difficult to machine, like cast iron.
· Small amounts of aluminum alloyed with delta-phase plutonium stabilize the
plutonium and produces a metal as machinable as aluminum. However, because
aluminum emits neutrons upon absorbing alpha particles from the decay of
plutonium, it raises the risk of pre-initiation, or early criticality, of the
plutonium trigger.
· Gallium alloyed with delta-phase plutonium retains the benefit of a product
nearly machinable as aluminum and far less prone to plutonium oxidation without
raising the risk of pre-initiation, and therefore the plutonium-gallium alloy
is the most common in plutonium pits.
To make plutonium fuel, DOE intends to destabilize plutonium by removing
gallium during purification.
Plutonium
Hazards
The
combination of radioactivity and chemical instability makes plutonium in the
workplace an inherently unsafe enterprise even after it is produced and
separated.
Add to this the need for precise accounting to the gram level and large
protective forces to guard vaults and other storage areas, and the costs of
dealing with plutonium become exorbitant.
Primary among the numerous aspects
of the plutonium radiation hazard is the fact that it takes 24,400 years for it
to lose one half of its radioactivity, meaning that it will remain dangerous
for hundreds of thousands of years and react adversely when exposed to common
environments.
Alpha
Radiation and Decay
Plutonium-239 emits high levels of
alpha radiation (Figure 1-3). Although alpha radiation can be stopped with
paper, it causes damage in many ways and from several phenomenon.
Figure
1-3. The first part of the plutonium-239 decay chain. Plutonium decays to
Uranium 238 by emitting an alpha particle, in this case a helium nucleus. The
energy from this process drives several reactions that are poorly understood.
1. Damage to the plutonium over time. The recoil energy from the decay
generates 85 kilo-electron-volts of kinetic energy in the uranium nucleus, of
which 60 keV remains when the nucleus collides within the matrix and displaces
plutonium atoms in the metal.ix Over the course of
decades, this action can damage plutonium enough to keep weapons designers
leery of the “reliability” of the plutonium triggers.
The helium nucleus has far more energy when released, 5 million-electron-volts,
but this is said to lose all but 0.1 percent of its energy through collisions
with electrons before capturing a few electrons and “settling in” as a helium
atom.x
Over the course of decades, helium atoms accumulate to the point of creating
bubbles, another grave concern of weapons designers. Helium buildup also poses
a health and safety risk. For example, in 1963 a plutonium pit tube broke
during a weapon disassembly process at Pantex and contaminated workers and the
facility with plutonium contaminated helium gas.
2. Damage to other metals
over time.
Plutonium decay basically damages everything in its path, and this impact is
most measurable on elements that experience “void swelling” from radiation,
meaning they swell in size over time.xi The effects of this over
the course of decades is poorly understood because plutonium has never been
allowed to age for decades, but some implications are obvious:
·
Beryllium, which is used as a neutron tamper within pits and
as cladding on many plutonium pits (see Part III) serving to protect the
plutonium from oxidizing, experiences “gas-driven” swelling;.
·
Aluminum, which is used in cladding on some pits, suffers
from void swelling.
·
Iron, Chromium, and Nickel, the key ingredients in stainless
steel used for plutonium storage cans, experiences void swelling;
·
Zirconium, used to clad nuclear fuel, experiences void
swelling.
3. Damage to live tissues. If the uranium nuclei from decay
damages metal as dense as plutonium, the impacts on living tissue are quite obvious.
Plutonium is said to be “harmless” if ingested as a metal, but this is an
obvious fallacy since even plutonium metal has a layer of plutonium oxide
present at all times,xii oxides are always
present to some degree on metals, and the chemical reactions with common
materials that worry metallurgists and weapons designers are certainly a
concern inside the human body.
Plutonium is most hazardous in a powder form. Much debate has occurred over how
much plutonium oxide can cause lung cancer within a few decades, with estimates
ranging from a few micrograms to 30-60 micrograms to 2 milligrams. There seems
to be little debate over how much will kill a person:
·
Ingestion of 500 milligrams, or one half of a gram, is
considered the acute lethal dose;
·
Inhalation of 20 milligrams is considered the acute lethal
dose;xiii
A good scale for reference is a
typical Sweet N’ Low packet which contains one million micrograms of sugar
substitute.
4. Radiolysis of common materials. Alpha particles react with
materials such as air and water to cause “radiolysis” of common materials
(Figure 1-4). Plutonium metal oxidizes readily in air and plutonium oxide
generates gases that can rupture storage containers. Plutonium is most
hazardous in a powder form.
Figure
1-4. Simplified illustration showing various reactions brought about by alpha
decay.
The literature is filled with reports about ruptured containers and massive
oxidation of entire metal pieces. For example, in 1983 Los Alamos reported the
formation of a black powdered suboxide in “casting skulls” left over from
plutonium pit fabrication, and when containers of skulls were opened, the
plutonium suboxide would ignite “almost explosively.”xiv
To avoid these undesirable reactions, DOE finally established a long-term
storage standard for plutonium in 1994, but has had trouble meeting that
standard (see Part II, Section B.) Called the 3013 standard, it requires that
plutonium metals and oxides be stored in two sealed metal containers free of
organic materials. Reaching this standard requires heating of oxides to
temperatures greater than 900 degrees Celsius.
A few near-term implications of this chemical fact include:
1. Nitric acid processing, which DOE plans to use to purify plutonium oxide as
the first step towards making plutonium MOX, greatly increases the likelihood
of explosions, spills, and criticality events. The plutonium pit disassembly
and conversion facility is planned as the main source of plutonium oxide for a
plutonium fuel (MOX) factory. Early plans for the PDCF require the plutonium
oxide product to meet the long term plutonium storage (3013) standard.xv
2. The dangers of nitric acid plutonium processing are aggravated if the
plutonium oxide was produced or treated at temperatures greater than 600
degrees Celsius. Oxides heated to temperatures between 600 and 1000 C “require
somewhat more stringent procedures” when dissolving in acids, and plutonium
oxide powder heated to temperatures over 1000 Celsius “require extreme
measures.”xvi Since the long-term storage standard requires plutonium to be heated at
temperatures well above 600 degrees C,xvii it is incompatible with the needs of plutonium fuel
production.
Aging
Plutonium and Americium-241
Plutonium-241, which is present in all grades of plutonium, decays into the
more radioactive and dangerous americium-241, an intense gamma ray emitter that
is 100 times more toxic than plutonium 239. Weapons plutonium was routinely
purified to eliminate americium, which of course produced stockpiles of
americium. If plutonium decay is allowed to run its course, radiation levels in
U.S. plutonium will peak in the next 38 to 60 years (Figure 1-4).
Figure 1-4. As plutonium-241
decays to Americium-241, weapon grade plutonium becomes more hazardous and
radioactive. Americium levels peak after 70 years.
One
fact that has become increasingly clear is that the plutonium hazard has more
depth and breadth. Not only is plutonium useable in nuclear weapons at the
scale of kilograms and acutely toxic at the scale of milligrams, it is also has
the most complex chemistry in the Periodic Table of the Elements (Pages 1.3 to
1.6). DOE officials who have told the public countless times that alpha
radiation can be blocked by a piece of paper have failed to inform people that
alpha radiation from the decay of plutonium 239 causes, over the course of
decades to centuries, damage to plutonium metal, any metal in contact or near
contact with plutonium, and adverse chemical reactions with our most common
elements, oxygen and hydrogen. All these things also make keeping track of
plutonium much more difficult.
If the alpha particles from the decay of plutonium 239 can damage the densest
metal on earth, the impacts of alpha radiation from plutonium ingested or
inhaled n the human body is obviously detrimental. Plutonium is often said to
be “harmless” if ingested as a metal, but this is an obvious fallacy since it
turns out that plutonium metal has a microscopic layer of plutonium oxide
present at all times. The chemical reactions with common materials that worry
metallurgists and weapons designers are certainly a concern inside the human
body.
Plutonium is most hazardous in an oxide powder form., with inhalation of only
20 milligrams enough to kill someone quickly (Page 1.6) and 30 to 60 micrograms
easily enough to greatly raise the risk of cancer. Yet, DOE is planning to
truck 3 metric tonnes of plutonium oxide from Rocky Flats to Savannah River
Site this year in its politically motivated rush to close Rocky Flats as soon
as possible.
Although the revelations about plutonium complexity has forced DOE to finally
establish a long term plutonium storage standard, it is pursuing projects at
odds with its own standards. The best example is DOE’s zealous pursuit of a
plutonium MOX fuel factory that utilizes surplus weapon-grade plutonium found
in plutonium pits.
To make this fuel requires nitric acid based plutonium processing that has
generated tremendous radioactive waste problems in the past, a process that
greatly increases the likelihood of explosions, spills, and accidental
criticality. Yet, the plutonium storage standard requires plutonium oxide to be
heated to temperatures that make nitric acid processing even more dangerous.
(Page 1.7). Instead of recognizing that plutonium fuel production from weapons
plutonium is incompatible with its own storage standard, DOE seems intent on
neglecting its commitment to safe storage in favor of its devotion to plutonium
fuel.
In the past five years, DOE has reneged on nearly every one of its plutonium
management decisions (see sidebar on Page iii) that did not involve spreading
the liability at Rocky Flats around the country as quickly as possible or
pursuing the dream of stuffing aging nuclear reactors one-third full of
plutonium fuel. While underfunding the most fundamental mission-safe and secure
storage-it has spent millions of dollars on unnecessary projects like gallium
removal experiments and an irrelevant MOX fuel test in Canada.
DOE has not released updated plutonium inventory figures in five years and has
even silently carved away bits and pieces of the declared surplus:
---In November 1999, DOE removed 3.8 (MMMMMMMT) of surplus plutonium found in
unirradiated nuclear fuel in Idaho (Page 2.9) which forced the planning team
for the plutonium immobilization plant at SRS to issue its third design; and another
0.6 to 0.8 MT of un-irradiated nuclear fuel at Hanford was removed for
“possible programmatic use.”
---In 1998 an undisclosed number of surrplus plutonium pits were recategorized
as “national security assets;” (Page 3.3)
---In 1998 the nuclear weapons program aaaat Los Alamos received “permission
from the politicians” to divert some “nickel-sized” pieces of plutonium from
its pit disassembly and conversion demonstration project for plutonium aging
studies in support of nuclear weapons stockpile stewardship; (Page 2-12).
DOE matched this failure to be up-front with its numbers with an aversion to
being up-front about the hazards of its proposals. During the Surplus Plutonium
Disposition Environmental Impact Statement process, DOE attempted to hide the
fact that plutonium pit disassembly and conversion involved tritium and
beryllium processing that would have meant a 10,000 fold increase in
radioactive air pollutants at Pantex and will mean that SRS will become a
certifiable beryllium site.
Broken Promises, Abandoned
Decisions |
|
|
|
|
|
|
|
Higher on the list was DOE’s selection of a nitric-acid based plutonium
conversion process for making Mixed Oxide (MOX) plutonium fuel in 1997.
Unfortunately, DOE did not inform the public of its decision until late in 1999
and then grossly underestimated the impacts of the operations.
But the most egregious example of dishonesty was the public presentation of
plutonium disposition facilities as nonproliferation missions while DOE
officials, at the urging of the Pentagon and Congress, secretly crafted a
parallel plan to produce new plutonium warheads. The possibility of SRS
dismantling plutonium pits for a few years and then putting new ones together
is very real. (Pages 3.15 to 3.19).
The list includes internal stonewalling, drastic funding cuts on fundamental
programs, constant redesign and “rebaselining,” and a plethora of
contradictions:
As a result of this investigation, BREDL is making the following
recommendations to the new administration in the hopes that health and safety
will take precedent over political expediency, that the fundamental issue of
safe and secure storage receives the highest priority, and that no more huge
sums of money are squandered:
1. There must be a renewed attitude towards increased openness and honesty in
the U.S. nuclear weapons complex and a reversal of the current trend against
openness.
2. DOE must publish its latest inventories of plutonium, uranium, and other
special nuclear materials and disclose any information suggesting that
diversion of materials has occurred. BREDL is making the following estimates
based on DOE’s figures in various reports, showing the sheer volume of
plutonium “items,” requiring individual handling at some point in time:
|
Plutonium Form |
#
Items |
Plutonium Content, MT |
Non-Pit Plutonium Solutions |
|
|
Metals |
6,361 |
8.6 |
Oxides |
12,537 |
6.35 |
Residues |
29,530 |
6.35 |
Unirradiated Fuel |
52,000 |
4.4 |
Plutonium Pits |
20,000 |
66.1 |
Irradiated Fuel |
|
7.5 |
Total |
120,528 |
99.8 to 100.0 |
3. Insure that DOE lives up to its promises and commitments made in
Environmental Impact Statements and in implementation Plans to the Defense
Nuclear Facilities Safety Board.
4. Make safe and secure storage of plutonium the number one priority in the
weapons complex.
5. Cease all efforts to pursue full-scale plutonium pit production and a
plutonium fuel economy and focus on reducing the plutonium hazard.
6. The inherent chemical instability of plutonium should be an added incentive
to make drastic cuts in the nuclear weapons arsenal.
-----------------------------------
Effective Nuclear Fuel Utilisation by DUPIC Cycle
A PWR is charged with fresh fuel of about 3.5% enrichment, which
is burned down to about 1.5% fissile content (0.9% U-235 and 0.6% Pu). It is
then discharged from the core at its end-of-life. The 0.9% residual U-235
enrichment is still higher than the natural U-235 concentration of 0.71%.
A normal CANDU reactor is loaded with natural uranium fuel, in
which the U-235 concentration is 0.71%. In contrast, the U-235 enrichment
concentration in PWR spent fuel is 0.9%, in addition to 0.6% newly generated plutonium.
Needless to say, we are also dealing with considerable amounts of fission
products, which are detrimental to reactivity maintenance and radiation
control.
Research is, therefore, being directed at making use of this
valuable unburnt fissile material in PWR spent fuel, by linking it with the
CANDU reactor system. This research is entitled DUPIC, which is an acronym for
Direct Use of PWR spent fuel In CANDU. The project is being conducted by a
tripartite group consisting of US, Canadian and Korean partners.
In Japan, there is a saying associated with business
administration, that is used to convey a desire to improve overall
productivity: "Further squeeze the dry floorcloth until you get the last
drop out of it." One could say that DUPIC resembles this dry
floorcloth-squeezing endeavour. One main difference, of course, is that LWR
spent fuel is not dry, but very wet, with lots of fissile nuclides in it. There
is a lot of juice to extract.
As you can see in Figure 1 below, the nuclide composition of
fissionable materials in CANDU spent fuel is 0.2% U-235 and 0.3% Pu. This
represents a significant squeeze of the fissile nuclides from PWR spent fuel,
that at the outset contained 0.9% U-235 and 0.6% Pu. The advantages of the
DUPIC fuel cycle include the following:
Figure 1: PWR-CANDU tandem fuel cycle by DUPIC
On the other hand, the
following must be borne in mind as we attempt to bring the DUPIC concept to
reality:
Unused uranium and plutonium can be extracted from spent
fuel by reprocessing, and recycled to produce more energy. This is being done
in a number of countries. The separated plutonium can be incorporated into new,
mixed oxide (MOX) fuel which is a combination of plutonium dioxide and uranium
dioxide.
A number of facilities, including
Sellafield in the UK and La Hague in France, separate uranium and plutonium
from spent fuel by chemical reprocessing. Several countries, including Belgium,
France, Germany and the UK, have developed the technology to make the plutonium
into MOX fuel. Currently, there are 34 reactors licensed to use MOX fuel and 25
others are in the licensing process. In addition, in OECD (Organisation for
Economic Co-operation and Development) countries, there are 165 more reactors
where licensing for MOX fuel is considered to be technically feasible.
Since 1963 some 400 tonnes of MOX
fuel has been loaded into reactors around the world. The principal benefits of
the MOX option are conservation of uranium, minimisation of high level waste
volumes and reduction of the world's separated plutonium inventory.
Substitution of MOX for uranium in nuclear fuel can result in a net reduction
in plutonium, since spent MOX fuel contains about one quarter less plutonium
than the original loading. A substantial part of this plutonium will be Pu-240,
rendering the mixture unsuitable for weapons.
After the uranium and plutonium
have been separated by reprocessing, there remain some radioactive wastes.
These are stored to allow their radioactivity to decay before permanent
disposal, for example in an underground repository.
Since nuclear fuel remains in a reactor for several years,
plutonium extracted from the spent fuel from nuclear power stations is
unsuitable for weapons manufacture. This is because it contains significant
quantities of Pu-240, which has physical properties that make the plutonium
unsuitable for use in nuclear weapons. By the time the fuel is removed from a
power reactor, as much as 40% of the plutonium it contains is Pu-240. Plutonium
for weapons is made in special reactors under conditions which do not lead to
the formation of more than a small amount of Pu-240.
Safeguarding of plutonium in the
nuclear power industry, which ensures that the material is not diverted to
nuclear weapons production, has built up an impressive record. To demonstrate
that they are not manufacturing nuclear weapons, essentially all countries with
nuclear power programs subject their nuclear facilities to the International
Atomic Energy Agency (IAEA) safeguards system. A function similar to that of
the IAEA is performed by the Euratom nuclear safeguards system. All commercial
nuclear material in the European Union is subject to active Euratom safeguards
inspections.
The US National Academy of Sciences estimated that in 1992
there were 1100 tonnes of plutonium in total from all types and sources,
including plutonium which has not been separated from spent fuel. This is
equivalent in energy potential to more than one billion tons of oil. It is estimated that within the world's total
plutonium inventory there is of the order of 200 tonnes of separated,
weapons-grade material. Over the past
few years, the dismantlement of excess nuclear warheads has left the United
States and Russia with large stocks of plutonium and highly enriched uranium
(HEU). These surpluses have re-ignited the debates around the world about the
use of plutonium as an energy source and provided new arguments for continued
assistance to on-going plutonium projects. This article reviews the basic facts
regarding plutonium use and provides some cost and technical analysis of the
issue.
About one-third of this is in the
USA and about two thirds in the former USSR. In addition, there are less than
100 tonnes of separated, reactor grade plutonium. As a result of existing
arms-control reduction commitments, approximately 100 tonnes of weapons-grade
plutonium are expected to become surplus to military needs.
--------------
In 1996 the Department of Energy (DOE) in which the
U.S. declared it had acquired 111.4 metric tonnes (MT) from four sources:
·
103.4 MT from government-owned plutonium production reactors
(36.1 MT at Savannah River Site (SRS) and 67.3 MT at Hanford);
·
0.6 MT from government-owned nonproduction reactions;
·
1.7 MT from commercial U.S. nuclear reactors that was
primarily received from West Valley, N.Y. reprocessing plant;
·
5.7 MT from foreign countries.
The active
military plutonium inventory held by DOE and the Department of Defense (DoD)
was declared to be 99.6 metric tonnes (MT), broken down into 3 categories.xviii
(Table 1-1).
Table 2-1. Declared Inventory,
1996. |
Grade |
% Plutonium-240 |
Total Pu, Metric Tonnes |
Weapons Grade |
< 7% |
85.1 |
Fuel Grade |
7-19% |
13.2 |
Reactor Grade |
>19% |
1.3 |
Total Plutonium |
99.6 MT |
This 99.6MT can be further broken
down into three major categories: the plutonium in nuclear weapons triggers
called plutonium pits, within irradiated nuclear fuel, or in non-pit form..
Table 2-2. Plutonium Inventory. |
Category |
Weapon Grade |
Fuel Grade |
Reactor Grade |
Total |
Pits |
66.1 |
0 |
0 |
66.1 |
Irradiated Fuel |
0.6 |
6.6 |
0.3 |
7.5 |
Non-pit |
18.4 |
7.6 |
0 |
26.0 |
Total |
85.1 |
14.5 |
0.3 |
99.6 |
Nonpit plutonium breakdown is
based on these three assumptions
(1) Assumes all plutonium in pits are weapon-grade, since U.S. is not known to
have developed plutonium weapons from non-weapon grade plutonium (although it did
test such weapons).
(2) Assumes that there is no non-surplus plutonium in irradiated fuel.
(3) DOE Plutonium vulnerability report cited 26.0 MT of non-pit Pu in DOE
complex.
Noting that due to “rounding” its figures did not always match up, DOE claimed
that 12.0 MT of plutonium has been “lost” or sent abroad, so the active
inventory is the acquired plutonium minus the following (note that DOE admitted
that due to rounding its figures did not always add up):
·
3.4 MT “expended” in wartime and nuclear weapons testing;
·
2.8 MT of plutonium DOE cannot account for called “inventory
differences;”xix
·
3.4 MT of plutonium in waste forms described as “normal
operating losses.”
·
1.2 MT of plutonium lost during nuclear reactor operations
described as “fission” and “transmutation”;
·
0.4 MT of plutonium that decayed to Americium 241 and
uranium 237.
·
0.1 MT of plutonium now in the hands of the U.S. civilian
industry;
·
0.7 MT of plutonium sent to foreign countries under
“agreements for cooperation,” i.e. the Atoms-For-Peace program;
Changes Since 1996
Last year DOE submitted a report
to Congress called the Integrated Nuclear
Materials Management Plan. The active inventory declared was the
same as that of 1996. This is unlikely to be the case for the following
reasons:
1. Contractors operating DOE plutonium sites are required to conduct
inventories on all Special Nuclear Materials (SNM) and report updated inventory
differences. For example, at Savannah River Site (SRS), the Materials Controls
and Accounting (MC&A) department is directed to “reconcile SRS nuclear
material records with NMMSS (U.S. Nuclear Materials Management Safeguard
System) semiannually” and “provide to OSS (Office of Security and Safeguards)
semi-annual reports on statistical analyses of inventory differences.”xx
Therefore the Department has updated figures on material-unaccounted-for (MUF),
now known as “inventory differences.”
The question that remains is: Does DOE
still have 2.8 MT of unaccounted-for plutonium?
2. In response to an investigation by the Institute for Energy and
Environmental Research (IEER), DOE acknowledged there is more buried plutonium
waste at Idaho, SRS, RFETS, and Hanford.xxi
Therefore, the amount of plutonium in waste is also likely to be higher, which
would mean lower inventory differences.
3. DOE has changed how it classifies waste vs. non-waste plutonium,xxii
and now appears intent on trying to send as much plutonium as waste to the
Waste Isolation Pilot Plant (WIPP) in New Mexico as possible.
4. Plutonium has done nothing but decay the last five years, so more has been
lost.
5. Stabilization efforts of non-pit plutonium should have led to better
estimates, especially considering the advances in technology for materials
accounting.
6. DOE opened a new plutonium storage site, the Waste Isolation Pilot Plant, in
New Mexico; where it intends to bury more than ten metric tonnes of plutonium
as waste.
Non-Pit Plutonium
The amount of non-pit plutonium is
complicated by several factors:
·
the inherent difficulty of measuring and accounting for
plutonium;
·
the fact that many materials with 10-30% plutonium content
are poorly characterized;
·
the changes in U.S. policy regarding waste vs. recoverable
materials;
·
whether plutonium in pits was a part of the declassified
inventory at Rocky Flats and SRS
·
The ownership of the plutonium within the DOE bureaucracy
and the lack of final decisions regarding the fate of numerous materials.
Confusion about Nuclear
Materials |
|
When Production Stopped
Prior
to 1990, when nuclear weapons production was in high gear, “the vast majority
of fissile material scrap and materials from retired weapons was recycled. It
was less costly to recover fissile materials from high assay scrap and retired
weapons than to produce new material. As a result, very little scrap containing
fissile material was considered surplus. Consequently, these materials were
designated, handled, and packaged for short-term storage.”
In 1989, when the U.S. stopped producing special nuclear materials and numerous
facilities were shut down, there was no long-term standard for storing
plutonium. In fact, not much thought was even given to storage until it became
a problem:
“the halt in weapons production that
began in 1989 froze the manufacturing pipeline, leaving it in a state that
posed significant risks. High quantities of fissile materials (approximately
13 tons of plutonium metals and oxides, 400,000 liters of plutonium
solutions, 130 tons of plutonium residues, HEU, and special isotopes) needed
attention.” xxiii |
By 1994 DOE had finally developed a standard for long-term storage-up to 50
years-of non-pit plutonium metals and oxides, commonly called the 3013
Standard. However, between 1989 and 1994 DOE made insignificant progress
resolving the actual problem.
Change began in April 1994 when the Defense Nuclear Facilities Safety Board
(DNFSB) issued its first Technical Report. Plutonium
Storage Safety at Major Department of Energy Facilities
addressed all unencapsulated, separated plutonium., leaving out plutonium in
pits, unirradiated nuclear fuel, and sealed sources. The report chastised the
DOE for not clearly recognizing many of the hazards associated with plutonium
storage, such as potential fires, explosions, and pressurization of containers.xxiv
(Three years later a major chemical explosion forced Hanford to shut down its
Plutonium Finishing Plant.)
A month later the Board issued Recommendation 94-1 for this plutonium and other
special nuclear materials. At the top of the list of nine recommendations
encompassed within 94-1 was the recommendation to:
“convert within two to three years the
materials...to forms or conditions suitable for safe interim storage. The
plan should include a provision that, within a reasonable period of time
(such as eight years), all storage of plutonium metal and oxide should be in
conformance with the draft DOE Standard on storage of plutonium now being
made final.” xxv |
Also in 1994 the DOE conducted a detailed plutonium vulnerability investigation
and published a landmark document of the results, including the detailing of
plutonium holdings down to the gram level at numerous “small holding” sites
documenting approximately 26.0 MT of non-pit separated plutonium.. In February
1995, a few months after publishing the vulnerability report, the Department
sent its first plan with new plutonium estimates (Table 1-3) for implementing
Recommendation 94-1 to the Defense Board, and acknowledged the urgency of the
issue:
“The
Department acknowledges and shares the Board's concerns and has developed this
integrated program plan to address these urgent problems.”xxvi
Table 2-3: Differences in separated, unencapsulated
Plutonium Inventory between DOE's Implementation Plan for Recommendation 94-1
and DOE's Plutonium Vulnerability Report |
Plutonium Form |
MT of Pu |
MT of Pu |
Oxide |
6.21 |
3.3 (1) |
Metal |
8.95 |
13.0 (1) |
Scrap/Residues |
6.34 (2) |
8.7 |
Solutions |
0.49 (2) |
0.7 |
Sealed Sources |
not reported |
0.05 |
Other Forms |
not reported (3) |
0.24 |
Total |
21.7 |
26.0 |
(1) These figures included
plutonium in unirradiated nuclear fuel. |
Not included in DOE's 94-1
implementation plan were 4.4 to 4.6 MT of plutonium in unirradiated fuel:
· 0.6 MT of plutonium in unused FFTF mixed oxxide fuel clad in 17,000 MOX fuel
pins at Hanford;
· 0.2 MT to 0.4 MT of plutonium in unclad FFTF fuel pellets at Hanford;
· 0.3 MT of unused ZPPR fuel in 21,000 pins of mixed oxide fuel in Idaho
(Figure 2-2)
· 3.5 MT of unused ZPPR plates within 29,000 plates of metal alloy fuel (Figure
2-3);
This provides more evidence that the 26.0 MT in the vulnerability report at
sites other than Pantex was non-pit plutonium and did not include plutonium in
pits, meaning that the original inventory at Rocky Flats was closer to 16.0 MT.
Implementation of DOE's nuclear materials stabilization plan has been hindered
by several factors, many of them political:
· The political decision to "accelerate closure"at Rocky Flats, with
an artificial deadline for closing all plutonium facilities by 2006;
· The political decision to pursue disposition of surplus plutonium through the
"dual-strategy" of both plutonium fuel use and immobilization;
· The lack of commitment to safe and secure storage within the Department of
Energy;
· The issue of who "owns" this plutonium, as it is managed by four
DOE departments Offices of Nuclear Energy, Defense Programs, Environmental
Management, and Fissile Materials Disposition.
· DOE's hopelessly fragmented approach to implementing the National
Environmental Policy Act (NEPA), with the total plutonium program being
addressed in several environmental impact statements.
· The 3013 standard has changed three times (3013-96, 30-13-99, and 3013-00).
· The nature of the materials, especially since the amount of plutonium
contained in the complex was minor compared to the total quantities of
materials that contained plutonium. (Figure 1-x_) .
· In 1999 DOE stopped construction of a cornerstone of its implementation plan,
the Actinide Packaging and Stabilization Facility (APSF), leaving a gaping hole
in the ground at Savannah River Site where excavation work was almost complete.
The fate of most of these materials remains unclear. One option is to dispose
more plutonium as a waste at the Waste Isolation Pilot Plant (WIPP) in New
Mexico. A more recent scheme proposed by the National Laboratories is to truck
hundreds of tonnes of residues to SRS and separate and purify the plutonium. in
the SRS canyons. The goal would be to increase-by 6-7 tonnes-:the amount of
weapons grade plutonium and improve our negotiating stance with Russia." xxvii
Because of the variations in DOE reporting, the actual inventory remains murky.
Following are BREDL's estimates for the total number of items containing
plutonium, and the plutonium content within those items.
Figure 2-1. This graphic
illustrates the quantity of materials compared to the plutonium in those
materials. Much of the non-pit plutonium is not weapons-usable, yet the
necessity to stabilize these materials from a health and safety standpoint
results in weapons-usable plutonium. Source: DOE/ID-10631, Plutonium Focus
Area. 1995.
Plutonium
in Solutions
In the plutonium vulnerability
report, DOE estimated a total of 700 kilograms (0.7 MT) of plutonium contained
in various concentrations within 400,000 liters of solutions with high risks of
criticality, explosions, and leaks:
· 143 kilograms at Rocky Flats
· 360 kilograms at Hanford
· a classified amount--estimated at approximately 200 kilograms--at Savannah
River Site;
DOE's contractors have stabilized 90% of the plutonium solutions in terms of
total volume, but only about 30 % of the
solutions in terms of plutonium content:
· 43 kilograms of plutonium remains at Rocky Flats in 2,000 liters of solution
in piping in 6 facilities;
· An estimated 110 kilograms of plutonium remains in H-Canyon at SRS in 34,000
liters of solution;*
· 341 kilograms of plutonium remains at Hanford's Plutonium Finishing Plant in
4,270 liters of solution
· A total of 494 kilograms, or approximately 0.5 MT, of plutonium in 40,270
liters of solutions.
Figure
2-2. Plutonium Ingots.
Plutonium
Metal
As of June 2000, DOE reported 8,951.3 kilograms (8.951 MT) of plutonium
metal contained in 6,361 items at 9 different sites:
· 6600 kilograms (6.6 MT) in 3403 containers at Rocky Flats;
· 700 kilograms (0.7 MT) in 475 containers in Hanford's Plutonium Finishing
Plant
· 1133 kilograms (1.133 MT) in 2060 containers at Los Alamos
· 490 kilograms (0.49 MT) in 230 containers at SRS
· 0.45 kilograms (0.00045 MT) in 210 containers at Argonne East National
Laboratory in Chicago;
· 20 kilograms (0.020 MT) in 50 containers at LLNL.
· 0.855 kilograms (0.00085 MT) in 20 containers at the Mound Plant in Ohio
· 0.3013 KG (0.0003 MT) in 30 containers at Oak Ridge;
· 6.7 kg (0.0067 MT) in 5 containers at Sandia National Laboratory. .
About 7.6 MT of this material is considered surplus, based on 28.9 MT of metals
declared surplus minus the 21.3 MT of surplus plutonium in pits at Pantex.
1.0 MT of this material is categorized as fuel-grade plutonium. In all
likelihood this includes the the 275 plutonium-aluminum alloy items at Hanford.
Table
2.4. Plutonium in Metals |
Site |
Pu Content in Metals, KG |
# of Pu Metal Items |
Rocky Flats |
6600.00 |
3403 |
Hanford |
700.00 |
339 |
Los Alamos |
1133.00 |
2060 |
SRS |
490.00 |
203 |
Argonne-East |
0.45 |
210 |
Livermore |
20.00 |
91 |
Mound |
0.86 |
20 |
Oak Ridge |
0.30 |
30 |
Sandia |
6.70 |
5 |
Total |
8591 |
6361 |
Plutonium Oxide
Figure
2-3. A can of plutonium oxide powder at Rocky Flats.
DOE has approximately 12,540 items
of plutonium oxides with greater than 50% plutonium content, for a total of
6.35 MT of plutonium. Virtually none of this plutonium meets the long-term 3013
storage standard:
· 3,200 kilograms (3.2 MT) of plutonium within 3,296 items content at Rocky
Flats;
· 1,500 kilograms (1.5 MT) of plutonium in 2,800 Pu oxide items and 2,300
plutonium-uranium oxide items at Hanford
· 800 kilograms (0.8 MT) of plutonium in 800 containers of Pu oxide at SRS;
· 721 kilograms (0.721 MT) of plutonium in more than 2,000 Pu oxide containers
at Los Alamos;
· 102 kilograms (0.102 MT) in 92 containers at LLNL;
· 28.1 kilograms (0.0028 MT) in 107 containers at Mound;
· 1.706 kilograms (0.0017 MT) in 83 containers at Oak Ridge;
· 1.4 kilograms (0.0014 MT) in 10 containers at Sandia National Laboratory; and
· 0.014 kilograms in 354 items at Lawrence Berkeley Laboratory.
Table
2.5 Plutonium in Oxides |
Site |
Pu
Content, KG |
#
of Items |
Rocky Flats |
3200 |
3296 |
Hanford |
1500 |
5100 |
Los Alamos |
721 |
2000 |
SRS |
800 |
800 |
Argonne-East |
0.48 |
695 |
Livermore |
102 |
92 |
Mound |
28 |
107 |
Oak Ridge |
1.7 |
83 |
Sandia |
1.4 |
10 |
Lawrence-Berkeley |
0.014 |
354 |
Total |
6355 |
12537 |
Plutonium in Unirradiated Nuclear Fuel
Figure 2-4. 21,000 ZPPR Fuel Pins
like the one pictured here are stored at Argonne National Laboratory West,
Idaho and contain a reported 0.3 MT of fuel-grade plutonium mixed with uranium
oxide to make Mixed Oxide (MOX) fuel.
As of June 2000, DOE had more than
50,000 items of clad, unused, unirradiated fuel containing a total of 4.4 to
4.6 MT of plutonium.
DOE's Office of Nuclear Energy retains control this plutonium. Until November
1999, the ZPPR fuels (Figures 2-4, 2-5) and FFTF Mixed Oxide (MOX) fuel (not
pictured) were scheduled to be processed at the Plutonium Immobilization Plant
at Savannah River Site. This idea was withdrawn in November 1999.
Figure 2-5. ZPPR Fuel Plates.
22,000 of these plates containing a reported 3.5 MT of plutonium are presently
stored at Argonne National Laboratory-West within the Idaho National
Engineering and Environmental Laboratory. The ZPPR fuel contains varying
percentages of uranium and plutonium alloyed with either aluminum or molybdenum
to make a material that is resistant to oxidation. Some plates are coated with
nickel to increase the resistance to oxidation. Source: UCRL-ID-131608, Rev. 3,
PIP-00-035
Processing
50,000 pieces of old unused fuel with high concentrations of americium-241
necessitated planning for remotely controlled processing of these materials.
Plans for dealing with such highly radioactive materials greatly contributed to
increased costs of a plutonium immobilization plant.
The cost of abandoning this path has not been determined. DOE is now considering
calling the ZPPR fuel a "national asset material" but has yet to
determine a future use.xxviii
Figure
2-6. Projected Feed for Plutonium Disposition.
Several assumptions lie within the
"nominal planning figures (figure 2-6):
· materials will be pre-processed
before the disposition steps begin. In other words, the planning figures are
based on expected conditions, not real conditions.
· included was 7.0 MT of metals "anticipated" to be surplus if START
II induced more weapons dismantlement;
· not included was the 7.5 MT of plutonium in irradiated fuel.
Figure
2-7. Office of Fissile Materials Disposition
Figure 2-8.
Office of Environmental Management.
Plutonium
Residues
Residues is a catch all phrase for
"material containing plutonium that was generated during the separation
and purification of plutonium or during the manufacture of plutonium-bearing
components for nuclear weapons."xxix
In 1990 these materials were assumed to have enough plutonium remaining to be
recoverable for future operations. Today, the plutonium cannot be used in
weapons without substantial processing and purification and it is mostly being
treated as waste.
Residues currently consist of an estimated 6.350 MT of plutonium in 29,530
items:
· 3000 kilograms (3.0 MT) in 20,532 items totaling more than 100 metric tonnes
of materials in Buildings 371 and 707 at Rocky Flats, of which nearly 10,000
items remain to be stabilized;
· 1,500 MT in 1300 containers at Hanford;
· 1,400 kg in nearly 6,000 items at LANL;
· 400 kilograms of plutonium in 1306 items of miscellaneous residues in the
F-Area at the Savannah River Site;xxx
· 35 kilograms in 202 items at LLNL;(114 cans of ash)
· 3 kilograms in 39 items at Mound;
· less than 1 kilogram in 12 items at Argonne East;
· 0.1 kg in 12 items at Oak Ridge;
· less than 1 kg in 250 items at Lawrence Berkeley;
This is the least certain and most poorly defined of all categories for the
following reasons:
1. With a few exceptions, this should be categorized as plutonium waste by U.S.
standards, since DOE intends to "dilute" most of the residues to
attain less than 10% plutonium by weight and therefore meet WIPP acceptance
criteria. The desire to "bury" nearly 7 MT of plutonium that would be
recycled under Russian policy clearly undermines claims made by U.S. plutonium
fuel advocates that Russia opposes the U.S. burying plutonium, and therefore
the U.S. must pursue the MOX plutonium fuel option.
2. Decommissioning of plutonium facilities across the nuclear weapons complex
will result in more plutonium wastes. This is because the category called
"holdup"-plutonium in pipes, glove boxes, ductwork, etc-has never
been quantified and is considered part of the unaccounted-for plutonium.
3. A recent proposal by DOE and its labs, called the 2025 vision, holds open
the prospects of processing much of the residues at the canyons at SRS in order
to increase weapons grade plutonium inventories.
Table
2-6. Plutonium in Residues |
Plutonium in Residues |
Site |
Pu
Content, KG |
#
of Items |
Rocky Flats |
3000 |
20532 |
Hanford |
1500 |
1313 |
Los Alamos |
1400 |
5900 |
SRS |
400 |
1270 |
Argonne-East |
0 |
12 |
Livermore |
35 |
202 |
Mound |
3 |
39 |
Oak Ridge |
12 |
12 |
Sandia |
0 |
0 |
Lawrence-Berkeley |
0 |
250 |
Total |
6350 |
29530 |
Plutonium in Waste:
In 1996 DOE estimated 3.4 MT of plutonium as "lost" through normal
operations and categorized as plutonium wastes (not including plutonium
released through smokestacks or in wastewater either routinely or by accident)
that are buried or stored at 8 sites:
· 1.522 MT buried or stored at Hanford;
· 1.108 MT buried or stored at Idaho National Engineering Laboratory; with
0.002 MT of this credited to ANLW;
· 0.610 MT buried or stored at Los Alamos;
· 0.575 MT buried or stored at SRS;
· 0.047 MT buried or stored at Rocky Flats;
· 0.016 MT stored at Nevada Test Site from past nuclear weapons accidents;
U.S.
Surplus Plutonium
U.S. surplus plutonium figures have changed substantially, although these
changes are obscured by unclear management plans. In 1996 the U.S. declared
38.2 MT of weapon-grade plutonium to be surplus. The common belief is that the
U.S. has 50 metric tonnes of surplus plutonium, but at no time did the U.S.
declare an active inventory of 50 metric tonnes of weapons-usable plutonium.
2.1 MT of the non-pit weapon-grade plutonium is estimated to be nonsurplus
based on the following:
· DOE declared 21.3 MT of plutonium at Pantex to be surplus, leaving 44.8 MT of
plutonium in pit form as stockpile plutonium;
· DOE declared 38.2 MT of weapon-grade plutonium to be surplus, leaving 46.9 MT
of weapon-grade plutonium as nonsurplus;
The
Nominal 50 MT
This confusion is a function of
DOE planning efforts. The Office of Fissile Materials Disposition spent five
years conducting environmental impact statements (EIS) on the plutonium
disposition options. The EIS processes consistently used 50.0 metric tonnes of
surplus plutonium as a "nominal planning figure,"xxxi
broken down as:
· 31.8 MT of "clean metal," mostly plutonium contained in weapon
components (pits), designated to the MOX route;
· 18.2 MT of plutonium contained in an array of forms considered physically
unsuitable or economically unfeasible to separate and purify for use in MOX and
designated for the immobilization disposition route.
The Real
Surplus
DOE did report approximately 52.5 metric tonnes (MT) of surplus plutonium (see
Table 1-5) that included:
· 38.2 MT of weapons-grade plutonium and 14.3 MT of fuel-grade plutonium.
· A net amount of surplus
weapons-usable plutonium in the existing inventory of 43.0 MT.xxxii
The 9.5 MT of plutonium not weapons-usable in its present state, broken down
as:
· 7.5 MT of plutonium contained in irradiated mixed-oxide (MOX) and metal alloy
fuel that already met the spent fuel standard.
· 2.0 MT of material commonly known as "residues" with low
concentrations of plutonium for "which extraction of plutonium would not
be practical and which is expected to be processed and repackaged for disposal
as TRU [transuranic] waste" at the Waste Isolation Pilot Plant in New
Mexico.
The
Changing Surplus
The following changes have occurred since the surplus inventory was announced:
1. There is now 3.0 MT of plutonium in residues scheduled for disposal at WIPP
and this material is identified as weapon-grade plutonium.. The addition of 1.0
MT to this route occurred when DOE rescinded its decision to send 1.0 MT of
plutonium in Rocky Flats "Sands, Slags, and Crucibles" to the
reprocessing canyons at SRS.
2. In 1997 Lawrence Livermore National Laboratory reported only 51.3 MT as the
"latest estimate"xxxiii
of surplus plutonium within a table identical to one in 1997,xxxiv
with the difference being the removal of 1.2 MT of plutonium in the following
forms:
· 0.8 tonnes of fuel-grade plutonium in irradiated fuel;
· 0.2 MT tonnes of fuel-grade plutonium in unirradiated reactor fuel;
· 0.1 MT of fuel-grade plutonium oxide;
· 0.1 MT of weapon-grade plutonium
metal;
The reasons
for this change are unknown and have not been explained by DOE.
However, in 1998 plutonium pits were reclassified (see Part 3) and some surplus
pits were reidentified as "national assets." Also, in 1998 Los Alamos
received "permission from the politicians" to divert some
"nickel-sized" pieces of plutonium from its pit disassembly and
conversion "disposition" demonstration project to its nuclear weapons
program for plutonium aging studies.xxxv
3. In November 1999, prior to issuing a Record of Decision on the SPDEIS in
January 2000, but after finishing the final SPDEIS, DOE removed the unirradiated ZPPR fuel plates and oxides pins from
the surplus inventory and declared it "Programmatic Use material."xxxvi DOE failed to mention this change
in its Record of Decision and apparently did not inform the designers of the
Immobilization Facility until after January 1, 2000.xxxvii
In June 2000 DOE submitted its Integrated Nuclear Materials to Congress in
which they described an active surplus plutonium inventory of 52.5 MT but added
the disclaimer that "a majority of the excess, approximately 48 MT, has no
programmatic use." DOE then described how it removed more than 4 MT from
the surplus inventory:
"A small portion of the 52.5 MT
supports programmatic uses such as basic scientific research, criticality
research, and production of medical isotopes. Most of this is in the form of
fuel for the Zero Power Physics Reactor (ZPPR) and Fast Flux Test Facility
(FFTF)."
"The Department is now considering
retaining the ZPPR fuel as a national resource at ANL-W. The Department is
currently preparing a Programmatic Environmental Impact Statement (PEIS) (DOE,
1999i) to consider the potential impacts of expanded nuclear facilities to
accommodate new civilian nuclear energy research and development efforts and
isotope production missions, including the role of the FFTF."xxxviii
Table 2-3 of this document identifies the ZPPR fuel as "in storage pending
future use."
The U.S.
Russian Agreement
Adding to the confusion is the U.S./Russian bilateral plutonium disposition
agreement signed on September 1, 2000. Plutonium "disposition" is a
catchphrase for putting plutonium in a highly irradiated storage environment.
Instead of 50 MT to be "disposed," the agreement calls for only
disposing 34.5 MT. DOE has continued to incorrectly declare 52.5 MT of surplus
plutonium in the active inventory (see Figures 2-7 and 2-8 on following page).
One unfortunate consistency in plutonium management has been overlapping and
poorly integrated bureaucracies. DOE's Office of Fissile Materials Disposition
(OFMD) and the Office of Environmental Management (EM) have never presented a
cohesive plan for managing non-pit plutonium to the public, and they can't seem
to agree on the numbers:
· EM incorrectly described the 14.3 MT of non-weapon grade plutonium as
"non-weapon-capable" even though DOE defines weapons-usable as "all plutonium except that present in spent
[irradiated] fuel and plutonium which contains greater than 10% plutonium
238."xxxix
·
Although WIPP was never said to be part of the fissile materials disposition
program in terms of surplus plutonium, both parties show 3.1 MT of
weapons-grade plutonium being disposed of at WIPP. OFMD's chart states the
material will be "diluted in waste" and sent to WIPP; whereas the EM
chart simply shows this waste being sent to WIPP;
· EM inaccurately claimed that 4.8 MT of reactor fuel was surplus.
Table 2.7. Non-pit Plutonium Inventory |
Plutonium Form |
#
Items |
Plutonium
Content, MT |
Metals |
6,361 |
8.59 |
Oxides |
12,537 |
6.35 |
Residues |
29,530 |
6.35 |
Unirradiated Fuel |
52,000 |
4.6 |
Total |
100,528 |
25.9 |
Table
2-8. DOE's Variety of Surplus Plutonium Numbers |
Form |
DOE's Official Estimate of
|
"Planning" Estimate of
Surplus Pu Total ** |
Amount for Disposition under
U.S./Russia Agreement |
Metal |
27.8 |
1.0 |
28.9 |
(1) 36.2 |
27.8 |
Oxide |
3.1 |
1.3 |
4.4 |
9.0 |
3.1 |
Reactor
Fuel |
0.2 |
4.4 |
4.6 |
4.8 |
0.0 |
Irradiated
Fuel |
0.6 |
6.9 |
7.5 |
0 |
0.0 |
Other
Forms |
6.4 |
0.7 |
7.1 |
0 |
4.6 |
Totals |
38.2 |
14.3 |
52.5 |
50.0 |
34.5 |
*Metal includes plutonium in pits, ingots, and buttons;
Oxide refers to plutonium oxide, reactor fuel refers to prepared but unused
MOX fuel, metal-alloy fuel elements, pellets, and MOX powder; and "other
forms" refers to uranium/plutonium oxides and "residues" from
the fabrication of weapon components. |
(1) This includes 7.0 MT "that may be declared
surplus in the future."(2) In 1997 DOE reported that 0.223 MT of
plutonium/uranium fuel material that had not been fabricated into finished
fuel components is part of the 4.8 MT total of unirradiated fuel and
therefore accounted for an additional
0.2 MT of reactor fuel in the planned category; xl |
Table
2-9. BREDL's Estimate of Active U.S. Plutonium Stockpile |
Form |
BREDL's Current Estimate of
Surplus Pu
|
Stockpile Pu
|
Amount for Disposition under
U.S./Russia Agreement |
Metal
in Pits |
21.2 |
0 |
21.2 |
44.9 |
0 |
44.9 |
21.2 |
Clean
Metal Oxide |
3.7 3.1 |
0 1.6 |
3.7 4.7 |
|
0 0 |
|
3.7 4.7 |
Impure
Metal |
2.8 |
1.0 |
3.87 |
0 |
0 |
0 |
2.8 |
Reactor
Fuel |
0 |
0.0 |
0.0 |
0.2 |
4.2 |
4.4 |
0.0 |
Irradiated
Fuel |
0.6 |
6.1 |
6.7 |
0 |
0.8 |
0.8 |
0.0 |
Residues |
6.5 |
0.7 |
7.2 |
0 |
0 |
0 |
0.4 |
Totals |
37.9 |
9.4 |
47.3 |
47.2 |
5.0 |
52.2 |
31.8 |
Nuclear Site |
Total Plutonium Inventory, in Metric Tonnes (1.1 English
Ton = 1.0 metric tonne) and
|
Hanford
(1) |
0.7 |
1.5 |
1.5 |
0.343 |
0.6 |
6.6 |
11.243 |
ANLW |
0.1 |
0 |
0 |
0 |
3.8 |
0.1 |
4.0 |
INEEL |
0 |
0 |
0 |
0 |
0 |
0.5 |
0.5 |
SRS
(2) |
0.490 |
0.800 |
0.400 |
0.110 |
0 |
0.3 |
2.1 |
PANTEX
(3) |
66.1 |
0 |
0 |
0 |
0 |
0 |
66.1 |
LANL
(4) |
1.1 |
0.7 |
1.4 |
0 |
0 |
0 |
3.2 |
LLNL
(5) |
0.020 |
0.102 |
0.035 |
0 |
0 |
0 |
0.4 |
RFETS
(6) |
6.6 |
3.2 |
3.0 |
0.043 |
0 |
0 |
12.9 |
TOTALS
(7) |
75.13 |
6.35 |
6.35 |
0.496 |
4.4 |
7.5 |
100.2 |
(1)
DOE reported 11.0 MT in 1996. The plutonium in solutions may be double
counted. |
Plutonium In Pits
Figure 3-1. Simplified illustration of a plutonium
trigger, or "pit", with storage "AL-R8" storage
container. Source: U.S. Department of Energy (DOE), Office of Fissile
Materials Disposition (OFMD). http://www.md.doe.gov |
Plutonium Pit
Basics
Describing Pits, No. 1 |
"Pits
can generally be characterized as nested shells of materials in different
configurations and constructed by different methods." Los
Alamos National Laboratory. ARIES Fact Sheet. 1997. |
Plutonium
pits are the triggers in most nuclear explosives. Pits are sealed weapon
components containing plutonium and other materials and came into being in
1956, replacing the plutonium "capsule" trigger design.xli
Pits are surrounded by carefully machined high explosive spheres. When the high
explosives are detonated the plutonium is compressed and imploded, thus
triggering the nuclear detonation (see Figure 1-1).
Describing Pits, No. 2 |
Rocky Flats described pits as a "pressure vessel
designed to withstand, without yielding, the boost gas or other operational
pressures which vary from weapon to weapon but are in the range of hundreds
of psi." Pits are also "designed to provide containment of the
radioactive materials to prevent the release of contamination or other unsafe
conditions." Other features of pits include: |
Pits were fabricated at the Rocky Flats plant in
Colorado from about 1954 to 1989, when safety and environmental problems forced
a production shutdown. Rocky Flats is infamous for thirty five years of unsafe
operations and costly accidents resulting in massive radiological
contamination, but in the nuclear weapons complex it is equally known for
producing high quality, "diamond-stamped" plutonium pits considered
the most durable and resilient parts of nuclear weapons.
There are about 48 different types of pits (see Table 3-1), each designed for
use in specific nuclear weapon systems and to be stored for 20 years or more
inside a weapon environment. Long-term storage (more than five years) of pits
outside of weapons is a program filled with uncertainties. Designers and
weaponeers within DOE refer to the variety of designs in terms of "pit
families,"with some more important variations including:
· shape and mass of the plutonium within the pit;
· the presence or absence of highly enriched uranium;
· the presence or absence of tritium;
· the type of metal cladding;
· bonded vs. nonbonded.
Pit numbers and DOE management
terminology
Normal
operations coupled with START I treaty between the U.S. and Russia turned the Pantex
nuclear weapons plant into a disassembly facility in the 1990's (Figure 3-2).
11, 875 weapons were dismantled, with most of the plutonium pits being sent to
"Zone 4" for "interim" storage.xlii
More than 11,000 plutonium pits accumulated at Pantex during this time, (Figure
3-2).
About 1200 pits were shipped to Pantex between 1997 and 1999 from Rocky Flats,
and another 60 pits were shipped from SRS to Pantex in 1998. Pantex in turn
shipped about 20 pits/year to Los Alamos for its surveillance/inspection
program, and an undisclosed amount (but less than 100) to Los Alamos for
plutonium pit disassembly and conversion demonstration program, leaving more
than 12,000 pits at Pantex today.xliii
Figure 3-2. Weapons Dismantlement
at Pantex, 1990's.
(427 dismantlements were scheduled for Year 2000).
DOE
now categorizes pits as surplus to military needs or as "national security
assets" (NSA), the latter a category concocted in 1998 and composed of:
· strategic reserve pits, including surplus pits considered defense program
"assets;"
· "enduring stockpile" pits that belong to existing weapon systems;
· "enhanced surveillance" pits that may include surplus pits.xliv
National Asset pits are scheduled to be stored indefinitely at Pantex in
retrofitted Building 2-116, possibly the most robust facility at Pantex but not
one without problems. At least one "national security asset" pit, the
problematic W-48, is not allowed in 12-116 because of heat concerns; and there
is no funding to move the national asset pits into 12-116 this fiscal year.xlv
The list of NSA pits is not constant, and the "design
agencies"-Lawrence Livermore and Los Alamos National Laboratories--have
failed to update their list of national security assets since February 1999,
leaving Pantex in the dark:
"an updated list has been requested by
letter, in briefings, and verbally to the person in charge of the list. To
date, an update has not been received. This is an open issue." xlvi
The total amount of plutonium in surplus pits was declared to be 21.3 MT in
1996. DOE maintains this number is current, but the reclassification of some
surplus pits as "national assets" leaves this questionable. If START
II arms reductions are implemented, another 7.0 MT of surplus plutonium in
about 2,000 to 2,500 pits is likely to be declared.
Surplus pits are scheduled to remain in Zone 4 at Pantex (see Pit Storage at
Pantex, page 3. )
until they are sent to a Plutonium Pit Disassembly and Conversion Facility
(PDCF) scheduled to open later this decade at Savannah River Site. (SRS).
Plutonium pit disassembly and conversion refers to "the removal of the
plutonium from the nuclear weapon pit and conversion [of the plutonium and
other parts] to an unclassified form that is verifiable in the sense that, containing
no classified information, the form can be examined by inspectors from other
nations." xlvii Size, shape, mass and isotopic composition
of the plutonium and other parts are considered traits in need of
declassification at the PDCF.
Table 3.1 Plutonium Pit Types in
U.S. Nuclear Weapons "Enduring Stockpile." |
Designer |
Warhead |
Container |
Unique Properties and/or Safety Issues |
Los Alamos National Laboratory B61-3,4,10 B61-7,11 |
125 |
2040 |
|
W76 |
116 |
2030 |
Most heat sensitive LANL design |
W78 |
117 |
2030 |
|
W80 |
124 |
2030 |
Responsibility being transferred to LLNL |
W80 |
119 |
2030 |
|
W88 |
126 |
2030 |
|
Lawrence Livermore B83 |
|
|
|
W62 |
MC2406 |
2030 |
|
W84 |
(1) |
unknown |
Fire Resistant Pit |
W87 |
MC3737 |
2040 |
Fire Resistant Pit. Unsuitable container. |
Container refers to the AL-R8
Subtype.li There are no replacements for
the 2040 at this time. Pit type ID's were determined from 1990 Rocky Flats
Safety Analysis Report for AL-R8's and from Dow and Salazar. Re: Storage
Facility Environmental Requirements for Pits and CSA's. August 22, 1995. |
Table 3.1.B: Plutonium Pit types
from retired weapon systems. |
Design Lab |
Warhead |
Pit Type |
Container |
Unique Properties and/or Safety Issues |
Los |
B28 |
83 |
2030 |
|
|
B28-0 |
93 |
2030 |
minimum decay heat load lii |
|
B43 |
79 |
unknown |
Beryllium cladding |
|
B43-1 |
101 |
2030 |
Beryllium cladding |
|
W33 |
unknown |
unknown |
|
|
W44 |
74 |
2030 |
Beryllium cladding |
|
W44-1 |
100 |
2030 |
Beryllium cladding |
|
W-50-1 |
103 |
2030 |
|
|
B54 |
81 |
2030 |
Pits require cleaning liii |
|
B54-1 |
96 |
2030 |
Pits require cleaning |
|
B57 |
104 |
2030 |
|
|
W59 |
90 |
unknown |
|
|
B61-0 |
110 |
2030 |
|
|
B61-2,5 |
114 |
2040 |
Unsuitable container, no replacement yet |
|
W66 |
112 |
unknown |
|
|
W69 |
111 |
2030 |
|
|
W85 |
128 |
2030 |
|
Lawrence |
W48 |
MC1397 |
2030 |
Beryllium clad pits, require cleaning prior to LTS |
|
W55 |
MC1324 |
2030 |
Suspected to be beryllium clad |
|
W56 |
MC1801 |
2040 |
High radiation pits, require cleaning prior to LTS |
|
W68 |
MC1978 |
2030 |
|
|
W70-0 |
MC2381 |
2030 |
|
|
W70-1 |
MC2381a |
2030 |
|
|
W70-2 |
MC2381b |
2040 |
Unsuitable container with no replacement yet |
|
W70-3 |
MC2381c |
2060 |
Suitability of container |
|
W71 |
Unknown |
Unknown |
Pits require cleaning |
|
W79 |
MC2574 |
2030 |
Suspected to be beryllium clad |
Plutonium Mass,
Beryllium, and HEU
Figure
3-3. Plutonium mass in pits is reduced through the use of neutron tampers.
Source: An Introduction to Nuclear Weapons. 1972.
The
amount, or mass, of plutonium that is inside of a pit varies and even the
average amount remains classified. But enough evidence exists to declare a
range of 1 to 6 kilograms (2.2 to 13.2 pounds) of plutonium mass in pits. Only
one kilogram of plutonium is necessary for a 1 kiloton explosion,liv
and Los Alamos defined a maximum material weight of 6 kilograms in pit shipping
containers.lv Considering there is 66.1 MT of plutonium in
approximately 20,000 plutonium pits, the average plutonium content is just over
3.0 kilograms per pit, or 6.6. pounds.
Two design variations can be used to decrease the plutonium mass:
1. Neutron tampers (Figure 3-3) are used to scatter escaping neutrons back into
the plutonium or HEU core after the nuclear chain reaction starts.lvi
One of the more common neutron tampers is beryllium, a highly toxic light
metal. Because classified nonnuclear pit parts will be "declassified"
at a PDCF by using furnaces to melt down the classified shapes,lvii
this operation poses extreme workplace hazards when the tamper is high-purity
beryllium (Figure 3-4).
|
Figure 3-4. How Toxic
is Beryllium? |
2.
The use of Highly Enriched Uranium (HEU), also known as "Oralloy, in pits
creates what are referred to as "composite
cores" and were a "major advance" in weapons design that reduced
the probability of pre-initiation of the nuclear explosive, and allowed for a
reduction in the amount of plutonium in the pit.lviii As a result, "the pits in the US stockpile can be generally
grouped into two types: (1) those containing weapons-grade plutonium and (2)
those containing weapons-grade plutonium and highly enriched uranium."lix
The presence of HEU in pits poses
accounting, handling, and classification problems at a PDCF.
In 1998 the ability to perform adequate materials control and accounting
measurements on incoming pits was found to pose a technically high risk at the
planned PDCF.lx This
risk is higher with HEU pits since there are no "proven techniques for
measurement" of this type. lxi
Having HEU parts in plutonium pits also necessitates decontamination of the HEU
to levels that meet strict acceptance criteria at the Y-12 plant at Oak Ridge,
Tennessee. The Y-12 plant is responsible for all storing all military HEU, it
is not a plutonium processing site, and designation as such would meet stiff
and justifiable resistance from the state and local communities.
Los Alamos encountered difficulties meeting the previous criteria of 20
disintegrations per minute of plutonium 239 in HEU metal, "with 30% of the
shipped parts presently being returned." However, the new limit for
plutonium contamination in HEU-oxide form has changed to 2.7 parts-per-million,
allowing plutonium levels "several orders of magnitude" higher than
the metal standard.lxii
Because of this issue, the final form of the HEU at a pit disassembly and conversion
plant was undecided as of a year ago. The decontamination methods under
consideration include:
· electrolytic etching, the current method at LANL that has achieved marginal
success at meeting metal acceptance criteria at Y-12 but generates less waste;
· Acid spray-leach; the historical process that involves spraying parts with
acid and then soaking in a diluted acid solution for up to three hours,
producing large volumes of liquid waste; or
· brushing of parts with a wire brush or blasting parts with "some
medium," both of which "are not expected to achieve the Y-12
acceptance criteria." lxiii
Plutonium Shape
Because
the critical mass for a spherical shape is "less than for any other
geometrical form of the given material,"lxiv
most pits are reported said to be spherical in shape. It is unlikely that
plutonium in pits are only spherical:
· Passive NMIS measurement systems are in development to estimate the shape of
plutonium assemblies inside of containers.lxv
· DOE continues to censor the discussion of shape of critical masses in the
sanitized version of Introduction to
Nuclear Weapons (Section 1.22).lxvi
· Criticality experiments at Rocky Flats in the 1960's included cylindrical
shapes of plutonium.lxvii
Isotopic Composition
The
amount of Plutonium-240 is the key isotopic variable in weapon-grade plutonium
because its high rate of spontaneous fission poses a higher risk of
"pre-initiation," or an early chain reaction, of the fissile
material. Higher quantities of plutonium-240 mean increases in critical mass
requirements, and therefore costs more to design, develop, and produce the
warhead.lxviii
Early
weapons had plutonium-240 content as low to 1.5% but more commonly 4-7%; and in
1972 the Pu-240 content in most stockpile weapons was said to be about 6%.lxix
The isotopic composition varied slightly according to the source of the
plutonium (Figure 3-5) and the design of the pit.
Figure 3-5. Variation in average
isotopic composition by source.
From: An Introduction to Nuclear Weapons. 1972.
During five years of Environmental Impact Statements, DOE never informed the
public that declassification of pits included declassifying the isotopic
composition. One month after the January 2000 Record of Decision to build a
PDCF at SRS was signed, the "blending" of plutonium oxides from two
or more pit types was required to declassify the isotopic composition of the
powder.lxx It is unclear whether this requirement is an
artifact of the Atomic Energy Act or a requirement for the plutonium fuel
factory.
Cladding and Beryllium Problems
The W-48 |
The pit for the W-48 nuclear artillery shell is a clad
with beryllium, and has created great problems at Pantex. In 1992 a W48 pit
cracked during a Pantex weapon disassembly operation that required rapid
cooling followed by rapid heating during removal of the high explosives. The
crack of 0.025 inch wide and 8.0 long in the outer beryllium shell resulted
in airborne plutonium contamination and was one of the rare accidents
involving pits. Afterward, a summer temperature limit of 150 degrees was
established for W-48's. In spite of these problems, DOE is retaining an
undisclosed number of W-48 pits as National Security Assets. |
Plutonium pits have an outer cladding of beryllium, aluminum, or stainless
steel. Vanadium is another cladding element, but it is unknown whether it is
just experimental or in use. Vanadium was used in 1993 during the W89 pit
re-use program at Pantex as a fire resistant cladding on W68 pits being
converted for use as W89 pits,lxxi
and the classified plutonium part inventory at RFETS presently includes six
Pu/Vanadium hemishells.lxxii
At least seven pit types are known or suspected to be clad with beryllium.
(Table 3.1.B),lxxiii posing the most significant problems with
storage and dismantlement of pits:
· pit disassembly can expose workers to highly toxic beryllium dust and fumes;
· beryllium clad pits appear to be more likely to require cleaning (see Table
3.1.B to remove any potentially corrosive organic materials, and pit cleaning
can expose workers to airborne beryllium;
· higher sensitivity to temperature fluctuations;
· increased risk of corrosion from chlorides and moisture which are found in
storage containers;
· pits clad with beryllium "are more vulnerable to fracture under impact
loading."lxxiv
Pits as a Heat Source
Pits that Heat Up |
|
Many pits are sensitive to temperatures, particularly
those clad with beryllium. Los Alamos and Lawrence Livermore have expressed
major concerns over heating of pits since early this decade.lxxv In 1995 Lawrence Livermore and Los Alamos National
Laboratories recommended temperatures between 65 and 75 degrees Fahrenheit for
storage buildings with strategic reserve pits, and less stringent
recommendations for "surplus" plutonium pits.lxxvi
In August 1998 an estimated thirty
plutonium "W76" pits were moved from one Pantex Zone 4
"bunker" to another "due to potential temperature concerns
during the recent heat wave."lxxvii The W76 pits are part of the large "strategic
reserve"of pits scheduled to be stored indefinitely at Pantex.
Tritium in Pits
In
1998 Los Alamos released a fact sheet that stated:
"A significant number of pits
processed by the ARIES facility will contain tritium."lxxviii
The "fact that tritium is associated with some unspecified pits" was
declassified in 1992.lxxix
During the Environmental Impact Statements for plutonium disposition, DOE
vaguely admitted that some plutonium pits were "contaminated" with
tritium and that these pits would have to be decontaminated; but finally
acknowledged that some pits contain tritium by writing:
"DOE knows
how many pits contain tritium."lxxx
The
reason for having tritium in pits by design is unknown but the impacts of this
design on the disassembly of plutonium pits are now more open.
Pits that contain tritium must be processed up-front in a highly secretive
"Special Recovery Line" where plutonium "is separated from
highly enriched uranium (HEU) and other parts and then processed in a vacuum
furnace that drives off tritium and produces a metal ingot. The tritium is
captured and packaged as a low level waste. The resulting plutonium ingot is
assayed and then reprocessed if it still contains tritium."lxxxi
This process was sufficiently difficult enough to dissuade Los Alamos from
processing pits containing tritium in its original ARIES demonstration project
when only 40 pits were planned for disassembly and conversion.lxxxii
The major environmental impact of this process is tritium air pollutants. In
the June 1998 Environmental Assessment for the plutonium pit demonstration
project at Los Alamos involving 250 plutonium pits over a four year period, DOE
reported air emissions of "up to 69 curies of tritium each year." In
the 1998 Draft SPDEIS, DOE buried the impacts in a source document by choosing
to omit a small table occupying less than a half-page reporting that 1100
curies of tritium will be emitted annually at a PDCF.lxxxiii
Tritium
Contamination vs. Pits that contain tritium
A
Model for the Initiation and Growth of Metal Hydride Corrosion.
LA-UR-00-5496. |
Pits could become contaminated if they contain tritium by design, or if they become
contaminated with tritium by accident. In any case, any kind of
hydrogen-plutonium reaction is undesirable because it could induce hydride
corrosion of the plutonium metal, causing pitting and a growth of hydride film
along the surface,"lxxxiv
as well as producing a pyrophoric plutonium hydride compound.
Bonded vs.
NonBonded Pits
DOE had declassified information about bonded weapon components prior to 1996.lxxxv
A 1998 Technical Risk Assessment of the Plutonium Pit Disassembly and
Conversion Facility identified the implications of this distinct design
variable when it identified an option with the least technical risk for
disassembly and conversion of most plutonium pit types. The Metal-Only Option
was suggested to process only "nonproblem pits" to produce only a
metal plutonium product and no plutonium oxide. This was because "many of
the pits, perhaps as many as 80%, can bypass the hydride/dehydride (conversion
to metal) module as the plutonium metal can be mechanically separated from the
pits."lxxxvi
The pit types where plutonium metal can be mechanically separated using a lathe
are called "non-bonded" pits; whereas the pits that require chemical
processing-either pyrochemical or liquid-to separate the plutonium in the pit
from other pit parts are called "Bonded" pits. In bonded pits, the
the plutonium is bonded to other metals in the pit, such as stainless steel,
beryllium, and/or uranium.lxxxvii
At least one Los Alamos source reports that all Russian plutonium pits are
nonbonded.lxxxviii
Figure
3-6. Plutonium Pit Bisector.
"The prototype bisector was designed and tested at Livermore. Using a
chipless cutting wheel, it can separate weapon pits into two half-shells in less
than 30 minutes so that the plutonium in them can be recovered for
disposition." Science and Technology Review. April 1997. Lawrence
Livermore National Laboratory.
Bonding and Pit Disassembly and
Conversion Issues
To avoid liquid acid "aqueous" processing of pits, Lawrence Livermore
National Laboratory developed the ARIES system that included a pit
"bisector" for cutting plutonium pits in half (Figure 3-6) --which
suggests that most or all bonded pits are of Livermore design.lxxxix
The bisector is the front end the Advanced Resource Integrated Extraction
System (ARIES) that DOE chose as a major part of the pit disassembly and
conversion process while it was still in the design and experimental phase.
Following the pit bisection, the plutonium must the be chemically separated
from the pit cladding and other pit parts. The two experimental technologies
proposed are hydride-dehydride, which recasts the plutonium as a metal, and
HYDOX, which utilizes the reaction of plutonium with hydrogen to produce a
plutonium oxide powder.
Do Bonded Pits Lack Tritium? |
|
Pit Tubes and
Pit Re-Use at Pantex
While DOE pursues plutonium pit fabrication at Los Alamos and possibly SRS, it
has abandoned, at least for now, the plutonium pit re-use project planned for
Pantex. A pit-re-use project occurred at Pantex in the early 1990's when Rocky
Flats was shut down. This project allowed DOE to proceed to complete the W-89
weapon program by re-using W68 pits and converting them to fire-resistant pits
by cladding them with vanadium. Heralded then as an innovative approach that
avoided messy pit fabrication, the latest plan for pit-re-use went unfunded in
fiscal year 2000,xc and there is no indication that DOE plans to
pursue this work, indicating a preference for new pit production at SRS.
One of the sticking points regarding pit-re-use involves pit tubes. Plutonium
pit tubes are designed to carry the booster tritium gas from the tritium
reservoir to the hollow core of the pit at the time of detonation. According to
pit-tube fabrication experts, pit tubes:
· are constructed of annealed type 304 stainless steel that is "very
ductile" and able to take severe deformation without cracking or leaking;
· are placed at assembly within tightly fitting slots in the high explosive and
must be straight and within true position within 0.02 in 1 inch.
· are usually of 0.12 inch diameter, for pressure testing, evacuation and
filling.
· are attached to stainless steel shell by TIG welding or electron beam welding
and to beryllium and aluminum shells by high temperature braze xci
.
Pit re-use was always described as "non-intrusive" during the
Environmental Impact Statement process. After Pantex was selected for the pit
re-use mission, the mission was renamed "pit requalification" and
changed from non-intrusive to intrusive because it included pit tube
replacement and refurbishment:
"SNM Requalification at PANTEX for FY
98 has been as continuation of the original
effort and has included an increase
in scope to address pre-screening, tube replacement and reacceptance...tube
replacement is a capability that was utilized at Rocky Flats. A similar
capability is being supported as a part of the Pit Rebuild program at LANL"
xcii
Figure 3-7. Sun-Woo,
Characterization of Stainless Steel 304 Tubing.
Pit tube replacement was
being advocated by Los Alamos prior to the funding cutoff for this program.
Because pit tubes are bent to very specific configurations and there is no
record of the number of times they have been bent, Los Alamos wanted to replace
all pit tubes. However, a LLNL report discussing the stainless steel used in
W87 pits reported that the tube would need to be bent at least ten times to
pose a great risk of failing (Figure 3-7). xciii
PLUTONIUM
STORAGE AT PANTEX: Stockpile Negligence?
Plutonium pits are multimillion dollar weapon components being stored in
substandard conditions.
Most pits are stored in the AL-R8 container (Figure 3-11) which is unsuitable
for long-term storage. Designed by Dow Chemical in the 1960's. AL-R8's are
unsealed and pits stored in them:
· require extra humidity and temperature controls
· are prone to corrosion because the internal celotex packing-sugar cane,
paper, starch, and wax--is a source of chlorides and moisture that can lead to
corrosion of the pit cladding.
· do not meet all safety criteria-specifically the 1100 pound dynamic crush
test.
· provide poor radiation shielding.
There are about 2,000 corroded AL-R8's at Pantex because they were procured
without the corrosion resistant liner.
Figure 3-8. AL-R8.
THE AT-400A Fiasco
DOE spent $50,000,000 designing and developing the
AT-400-A (Figure 3-9) dual-use shipping and storage container for plutonium
pits. Its advantages included:
· a sealed, inert gas environment that would prevent corrosion and other
degradation of pits
· better radioactive shielding;
· a 50-year design life.
It's disadvantages included cost ($8,000/unit) and problems associated with the
weld-possible burn through of the containment vessel.
DOE estimated that 2,000 plutonium pits per year could be repackaged in the
AT-400A, leaving pits in the safest container within a five year period. After
the repackaging startup was delayed by more than a year, 20 pits were
repackaged in a pilot run before DOE pulled the plug on the entire program.
Twenty W-48 pits remain in AT-400A's.
Figure 3-9. AT-400A
The Sealed Insert
Figure
3-10. AL-R8 with Sealed Insert, 2030 model. There is still a need for 2040
models for several pit types, including national asset pits
DOE replaced the AT-400A with the AL-R8 Sealed Insert (Figure 3-10). It is a
significant improvement over the AL-R8 because of the sealed, bolted, stainless
steel inner container, but is still not considered worthy of shipping
certification. Problems now plaguing this program include xciv
:
· a lack of funding to buy new containers at a cost of $2800/unit.
· the need to certify larger "2040-type"AL-R8 sealed inserts for
about several pit types ome pits, including most stockpile pits;
?
Figure 3-11. DOE still has no pit shipping container
· the lack of a pit cleaning station for 1500 pits too dirty for long term
storage, so Pantex is having to double-handle some pits;
· a lack of funding for labor, so Pantex is not able to run two shifts;
· a lack of funding for monitoring;
· limited funds for dealing with another cracked pit.
· DOE has only 300 shipping containers called FL's, the certification for the
FL's expires in 2002, and more than 200 of these were recently found to not
match design drawings;
Figure
3-12. Zone 4 Bunkers at Pantex. Plutonium pits are literally stacked to the
ceilings in these WWII and 1960's vintage bunkers. All but a few of these
facilities lack required humidity or temperature controls, and are unlikely to
withstand an aircraft crash - a serious issue due to the proximity of Amarillo
International Airport. Pantex has little space for additional pits.
· DOE has made no reported progress developing a new shipping container (Figure
3-11) to replace the FL and AT-400A.;
· a planned upgrade to Building 12-66 at Pantex was abandoned after the design
work was complete, leaving decades-old bunkers as the main storage buildings.
(Figure 3-12) These facilities were not supposed to be used after the Year
2000, but will be used indefinitely.
DOE's Dirty
Plutonium Secret
Plutonium Pit Production at Savannah
River Site
In the newly downsized U.S. Nuclear Weapons Production Complex, Savannah River
Site is the only remaining major plutonium processing site in the country and
is in line for three new facilities promoted as "nonproliferation"
missions:
a Plutonium Pit Disassembly and Conversion Facility that will process surplus
plutonium pits and convert the plutonium in those pits to an unclassified
plutonium oxide powder.
b Mixed Oxide (MOX) Fuel Fabrication Facility where "pure" or nearly
pure surplus plutonium will be purified using liquid acid processing and then
mixed with uranium to make MOX plutonium fuel for nuclear reactors;
c. A Plutonium Immobilization Plant (PIP) where impure and very difficult to
purify surplus plutonium will be mixed with uranium and a "titanate"
ceramic to make ceramic "pucks." (See below for explanation of can in
canister)
Tritium production and recycling is said to be the only nuclear weapons
production mission at SRS. However, because Rocky Flats no longer produces
nuclear weapons triggers called plutonium pits, new pit production is slated
for SRS, and this would inevitably involve the PDCF, making it a dual-use
facility:
Plutonium Aging
and ARIES as a Weapon Program
In 1998 the Government Accounting Office reported
that:
"DOD
was concerned that the aging of pits was not clearly identified in our report
as
a driving force of pit-production requirements. DOD said that it could not give
detailed pit-manufacturing requirements until the lifetime of pits is specified
more clearly by DOE."
DOE plans to spend over $1.1 billion through fiscal year 2007 to establish a
20-pits-per-year capacity. But this budget does not include disassembly work
xcv which is clearly being funded by OFMD under
the ARIES development. In addition, plutonium pit enhanced surveillance
program, a SSM program, ARIES was identified as a "pertinent task"
for the "Pit Focus Program."
material property data from pits dismantled in the ARIES process in order to
expand the age-
correlated database of applied plutonium properties.xcvi
Chairman Spence
and the Foster Panel
In 1996 Chairman of the House National Security Committee Floyd Spence (R-South
Carolina) issued a report titled "The
Clinton Administration and Stockpile Stewardship: Erosion by Design," in
which he wrote that,"Unprecedented reductions and disruptive
reorganizations in the nuclear weapons scientific and industrial base have
compromised the ability to maintain a safe and reliable nuclear
stockpile...unlike Russia or China, the United States no longer retains the
capacity for large-scale plutonium "pit" production and DOE's plans
to reconstitute such a capacity may be inadequate."
In December 1999 a congressional panel called the Foster Panel published "FY 1999 Report of the Panel to Assess the
Reliability, Safety, and Security of the United States Nuclear Stockpile,"
recommending that DOE:
"immediately begin the conceptual
design phase of a pit production facility adequate to meet national security
needs." xcvii
The Chiles
Commission
Another vote for pit production was cast by the Chiles Commission, which was
established to review the nuclear weapons workforce and determine needs and
priorities. The Commission concluded in 1998 report that, "large numbers
of workers are reaching retirement and a new generation of workers must be
hired and trained in order to preserve essential skills." One of these
essential skills is the machining of "materials unique to nuclear
weapons," such as plutonium, highly enriched uranium, and beryllium. Their
recommendations called for a renewed emphasis on plutonium pit production:
"DOE needs to give a much higher
priority to detailed planning for the production of replacement weapons
components. In the absence of such planning, the sizing of the nuclear weapons
workforce at the production facilities is left unnecessarily uncertain" xcviii
The SRS
Strategic Plan
The Savannah River Site is very explicit about its potential pit production
mission within some documents but does not publicize its intentions in an
up-front manner. The Savannah River Site
Strategic Plan: A Strategic Plan for 2000 and Beyond xcix
lists three focus areas for SRS:
· Nuclear Weapons Stockpile Stewardship
· Nuclear Materials Stewardship
· Environmental Stewardship
The plan states that Nuclear Weapons Stockpile Stewardship "emphasizes
science-based maintenance of the nuclear weapons stockpile. SRS supports the
stockpile by ensuring the safe and reliable recycle, delivery, and management
of tritium resources; by contributing to the stockpile surveillance program;
and by our ability to assist in the development of alternatives for large-scale
pit production capability, if required. associated with products and services
essential to achieving the Department of Energy's (DOE) goals."c
Under Goals, Objectives, and Strategies, the strategic plan states as a goal:
"Consolidate existing facilities and
plan, design, and construct new facilities to support current and future
stockpile requirements."
Within this goal is the objective to:
"Support the development of
contingency plans for a new pit production facility to meet future stockpile
requirements as national needs emerge."
Within this objective is the strategy to:
"Develop partnerships with the
national weapons laboratories and Oak Ridge Y-12 Plant to outline roles for
each organization in a large- scale pit manufacturing project."
Preparing for
Pit Production at SRS?
Several
operations at SRS suggest that the site is quietly and surreptitiously
implementing its strategic plan as it relates to large-scale plutonium pit
production:
1. Developing Plutonium Casting
Capability. An essential part of plutonium pit fabrication is
"casting plutonium metal feed ingots after adding gallium to the plutonium
metal and shape-casting the feed ingots into hemishells."
The Los Alamos Perspective |
|
|
In 1998 SRS developed the capability to recast plutonium metal in the FB-Line
"using an M-18 reduction furnace with a new casting chamber." Plutonium
metal is recast by charging a standard FB-Line magnesia crucible and placing
the charge in the casting chamber. In October 1998, "a [plutonium] button was produced by combining plutonium and
gallium metals to produce an alloy in which the plutonium is stabilized in the
d phase. Delta (d ) phase metal is not susceptible to low temperature induced
phase changes like a phase metal." ci
This effort was portrayed by SRS only as a contingency for plutonium metal
storage and not as a dual-purpose program that integrated storage goals with
pit production goals:
The capability to produce d stabilized
metal in FB-Line would provide a contingency for plutonium metal storage at the
SRS in the event that experimental programs show that the a to b phase
transition (and resulting decrease in density) has the potential to create
harmful mechanical stresses in storage containers. The continued use of the
casting process for the declassification and consolidation of plutonium from
weapons components also provides a disposition path for classified metal parts
and alloys currently stored at the RFETS." cii
2. Measuring Plutonium Density in Pits.
Another capability SRS has developed is a new measurement system for
determining plutonium density in finished plutonium pits. The Savannah River
Technology Center (SRTC) and Los Alamos undertook a collaborative research
project in which SRTC designed, fabricated, and tested a gas pycnometer
"to be used to measure densities of surrogate [plutonium pit] parts."
The project's objective was to find a more environmentally friendly method for
measuring the density of plutonium hemishells in pits. ciii
The plutonium density project is not a dual-use program, and is only necessary
for plutonium pit fabrication. Although the project occurred prior to the
issuance of the SRS strategic plan, it clearly is an example of collaborating
with the national laboratories to define roles for pit production.
3. The Plutonium Pit Disassembly and
Conversion Facility. Every analysis of plutonium pit production
lists pit disassembly as the first step in the process. For example, a joint
paper issued by Lawrence Livermore and Los Alamos National Laboratories
specified the first two steps of pit fabrication as:
· dismantlement of the pit;
· conversion of the metal through hydride and oxidize to plutonium oxide
(HYDOX) or hydride and reduce to metallic plutonium (HYDEC); civ
4. The Plutonium MOX Fuel Factory.
The capability to purify plutonium for pit fabrication is the missing
ingredient in the current version of the PDCF is plutonium purification
processing. However, the planned plutonium fuel factory will have the
capability to purify plutonium oxide powder.
Endnotes
i. For in-depth overviews of plutonium and other special nuclear materials,
see:
International Physicians for the Prevention of Nuclear War. 1992. Plutonium, Deadly Gold of the Nuclear Age.
(Second Printing with Corrections in 1995).
Nuclear Wastelands.
ii. Avens, Larry R. and P. Gary Eller. 2000. A
Vision for Environmentally Conscious Plutonium Processing. Los
Alamos National Laboratory. In: Challenges
in Plutonium Science. Los Alamos Science. Number 26. 2000. Page
436.
iii. Minutes of the Plutonium Information
Meeting. Rocky Flats Plant. January 29-30, 1959. Sanitized version
from DOE Archives.
.
iv. DoD Militarily Critical Technologies list. Nuclear Weapons Technology.
Section 5.
v. Lawrence Livermore National Laboratory. Stockpile
Stewardship Program. UCRL-LR-129261. 9781
vi. Hecker, Sigfried. 2000. Los Alamos Science. Number 26, and Plutonium Aging: From Mystery to Enigma.
LA-UR-99-5821. 1999.
vii. Condit, R.H. 1993. Plutonium: An
Introduction. Lawrence Livermore National Laboratory.
UCRL-JC-115357. Prepared for submittal to the Plutonium Primer Workshop. DOE
Office of Arms Control and Proliferation in Washington, D.C. on September 29,
1993.
viii. U.S. DOE. Plutonium, the First Fifty
Years; 1996; and Declassification of Plutonium Inventory at Rocky Flats,
Colorado, 1994.
ix. Radiation Effects in Plutonium.
Los Alamos Science. Number 26.
x. Ibid.
xi. Ibid.
xii. Haschke, John. 2000. The Surface
Corrosion of Plutonium. Los Alamos Science. No. 26.
xiii. Condit, R.H. 1993. Plutonium: An
Introduction; and Plutonium Storage by John
M. Haschke and Joseph C. Martz.
xiv. LA-3542. Plutonium Processing at LANL.
1983.
xv. Westinghouse Savannah River Company. 2000. Facility Design Description for Pit Disassembly and Conversion
Facility. February 24, 2000. Page 55.
xvi. Plutonium Processing at LANL . 1983.
xvii. DOE Standard 3013.
xviii. U.S. Department of Energy. Plutonium.
The First 50 Years. DOE actually declared 99.5 MT but this did not
include 0.1 MT of “classified transactions.”
xix. Inventory Differences used to be called “Materials Unaccounted For”
xx.Savannah River Site FY 2001 Annual Operating Plan. Summary Task Description Sheet. SOXX.
MC&A.
xxi. http://www.ieer.org
xxii. This graphic illustrates the fine line between “waste” and “residues.”
Historically much of what is now called “residues” would have been recovered by
purifying the plutonium. Russia’s policy is to recover plutonium from all forms
until there is less than 200 ppm of plutonium remaining. Only then does it
become a waste.
Integrated Nuclear Materials Management
Plan. June 2000.
xxiii. DOE/ID-10631. Revision 0 October 1998 Plutonium Focus Area
xxiv. Defense Nuclear Facilities Safety Board. Technical Report 1. Plutonium Storage Safety at Defense Nuclear Facilities.
April 1994.
xxv. Defense Nuclear Facilities Safety Board. Recommendation 94-1. May 26,
1994.
xxvi. U.S. DOE. Implementation Plan for DNFSB Recommendation 94-1. February,
1995.
xxvii. Christenson, et al. 2000. Managing the Nation’s Nuclear Materials. The
2025 Vision for the Department of Energy. LA-UR-00-3489. http://lib-www.lanl.gov/la-pubs/00393665.pdf.
.
xxviii. U.S. DOE. 2000. Integrated Nuclear
Materials Management Plan. Submitted to Congress, June 2000.
xxix. DOE 94-1 Implemnetation Plan. Revision 3.
xxx. DNFSB. Recommendation 2000-1.
xxxi. U.S. DOE. Office of Fissile Materials Disposition. Draft and Final Surplus Plutonium Disposition
Environmental Impact Statements (SPDEIS), 1997-1999.
xxxii. U.S. DOE. Office of Fissile Materials Disposition. 1997. Feed Materials Planning Basis for Surplus
Weapons-Usable Plutonium Disposition. April 1997.
.
xxxiii.
xxxiv
xxxv. Olivas. Plutonium Aging.
xxxvi. Letter, William D. Magwood,
DOE, Office of Nuclear Energy, to Laura S. H. Holgate, DOE, Office of Fissile
Materials Disposition, "Zero Power Physics Reactor (ZPPR) Plutonium
Fuel," November 12, 1999. Referred to in the November 2000
SRS Pu Storage Plan.
xxxvii. Design Only Conceptual Design
Report for Plutonium Immobilization Plant. February 2000. Revision
1.
xxxviii. Integrated Materials Plan.
Page 2-4.
xxxix. Gray, L.W. et al. 1999. The Blending
Strategy for the Plutonium Immobilization Program.
Paper prepared for submittal to the Waste Management ‘99 Symposium, Tuscon,
Arizona. February 28-March 4, 1999. UCRL-JC-133279. Lawrence Livermore National
Laboratory.
xl
xli. U.S. Atomic Energy Commission Nuclear Safety Working Group. 1956. A Preliminary Consideration of the Hazards of Sealed
Pit Weapons. Sanitized Version from DOE Archives.
xlii. Pantex was selected as the long-term storage (up to 50 years) facility
for plutonium pits in the January 1997 Record of Decision for the Programmatic Environmental Impact Statement for
Storage and Disposition of Weapons-Usable Fissile Materials; and
under the Pantex Plant Sitewide Environmental Impact Statement (January 1997),
up to 20,000 plutonium pits can be stored there.
xliii. Pantex now claims that total pit numbers are classified.
xliv. Mason and Hanger Corporation. 2000. Pantex
Pit Management Plan. Final Revision 3. October 27, 2000. Pantex
Nuclear Materials Department. Page 38.
xlv. Ibid. Page 42.
xlvi. Ibid. Page 43.
xlvii. Toevs, 1997. LA-UR-97-4113. Surplus
Weapons Plutonium: Technologies for Pit Disassembly and Conversion and MOX fuel
Fabrication.
.
xlviii.
xlix. Ibid. All pit type ID’s obtained from this source or otherwise noted.
l. Rocky Flats Safety Analysis Report for the AL-R8 Container. 1990.
li. Ibid.
lii. Ibid.
liii. Mason and Hanger Corporation. 2000. Pantex
Pit Management Plan.
liv. Institute for Energy and Environmental Research. Plutonium Fact Sheet.
lv. Data Call for Stockpile Stewardship Management Programmatic Environmental
Impact Statement. Los Alamos Plutonium Pit Production. 1995.
lvi. Glasstone and Redman. An Introduction
to Nuclear Weapons. June 1972. Atomic Energy Agency. Sanitized
Version from DOE Archives.
lvii. Westinghouse Savannah River Company. 2000. Facility Design Description for Pit Disassembly and Conversion Facility.
February 24, 2000. Page 55.
lviii. Glasstone and Redman. An
Introduction to Nuclear Weapons.
lix. LA-UR-00-504 January 2000 Safeguards
and Security Program Quarterly Activity Summary October 1-December
31, 1999.
lx. Ibid.
lxi. Ibid.
lxii. Wedman, Douglas E. and Steven D. McKee. Uranium
Disposition Options for a Pit Disassembly Facility. LA-UR-00-128.
February 200.
lxiii. Ibid.
lxiv. Glasstone and Redman. An Introduction
to Nuclear Weapons.
lxv. Mattingly, et al. 1998. Passive NMIS Measurements
to Estimate the Shape of Plutonium Assemblies (Slide Presentation.)
Y-12 Oak Ridge Plant. November 25, 1998. Y/LB-15,998.
lxvi. Glasstone and Redman. An Introduction
to Nuclear Weapons.
lxvii. Minutes of Plutonium Information
Meeting. Rocky Flats Plant. June 29-30, 1959. Issued August 7,
1959. DOE Archives. Sanitized Version.
lxviii. Glasstone and Redman. An
Introduction to Nuclear Weapons.
lxix. Glasstone and Redman. An Introduction
to Nuclear Weapons
lxx. Westinghouse Savannah River Company. 2000. Facility Design Description for Pit Disassembly and Conversion
Facility. February 24, 2000. Page 55.
lxxi. Pit Resuse Station. 1993.
lxxii. 3/26/99 letter from DOE to DNFSB: Classified Plutonium at Rocky Flats.
lxxiii. Pits are “suspected to be clad with beryllium” in this report if they
were separated from the high explosives using similar technologies as the W-48.
lxxiv. Rocky Flats Safety Analysis Report for the AL-R8 Container. 1990.
lxxv. Buntain, G., et al 1995. Pit Storage Monitoring. LA-12907
UC-721 April 1995.
lxxvi. Dow, Jerry (LLNL) and Lou Salazar (LANL). Letter to Department of
Energy. Re: Storage Facility Environmental
Requirements for Pits and CSA’s. August 22, 1995.
lxxvii. Defense Nuclear Facilities Safety Board. Pantex Plant Activity Report for Week Ending July 10, 1998.
lxxviii. ARIES Source Term Fact Sheet
(LALP-97-24, Rev. 3, April 24, 1998).
lxxix. http://www.osti.gov/html/osti/opennet/document/rdd-1/drwcrtf3.html#ZZ1
lxxx. SPDEIS. Page 3-923.
lxxxi. Los Alamos National Laboratory and Fluor Daniel, Inc. 1997. Design-Only Conceptual Design Report for the Pit
Disassembly and Conversion Facility. Project No. 99-D-141. Prepared
for the DOE Office of Fissile Materials Disposition. December 12, 1997.
lxxxii. ARIES Source Term Fact Sheet
(LALP-97-24, Rev. 3, April 24, 1998).
lxxxiii. The tritium data was contained in Pit
Disassembly and Conversion Facility EIS Data Report. LA-UR-97-2909.
The Draft SPDEIS referred to this document on Page 3-4.
lxxxiv. Tanksi, John A. 2000. A Model for
the Initiation and Growth of Metal Hydride Corrosion.
LA-UR-00-5496. 23rd DOE Aging, Compatibility, and Stockpile Stewardship Conference.
November 14-16, 2000.
lxxxv. http://www.osti.gov/html/osti/opennet/document/rdd-1/drwcrtf3.html#ZZ1
1) Fact that bonding of plutonium or enriched uranium to materials other than
themselves is a weapon production process. (93-2)
(2) Fact that such bonding occurs or may occur to specific unclassified tamper,
alpha-barrier or fire resistant materials in unspecified pits or weapons.
(93-2)
(3) Fact that plutonium and uranium may be bonded to each other in unspecified
pits or weapons. (93-2)
(4) Fact that such bonding may be diffusion bonding accomplished in an
autoclave or may be accomplished by sputtering. (93-2)
(5) Fact that pit bonding/sputtering is done to ensure a more robust weapon or
pit. (93-2) (6) The use of autoclaves in pit production. (93-2)
(7) The fact that plutonium is processed in autoclaves. (93-2)
(8) The fact that sputtering of fissile materials is done at or for any
Department of Energy facility as a
production process. (93-2)
(9) The fact of a weapons interest in producing a metallurgical bond between
beryllium and plutonium. (93-2)
(10) The fact that beryllium and plutonium are bonded together in unspecified
pits or weapons. (93-2)
(11) Routine data concerning concentrations of beryllium in plutonium higher
than 100 ppm. (93-2)
lxxxvi. Kidinger, John, ARES Corporation, John Darby and Desmond Stack, Los
Alamos National Laboratory. 1997. Technical Risk Assessment for the Department
of Energy Pit Disassembly and Conversion Facility Final Report. September,
1997. LA-UR-97-2236. (TRA or Technical Assessment)
lxxxvii. Toevs, 1997. LA-UR-97-4113. Surplus Weapons Plutonium: Technologies
for Pit Disassembly and Conversion and MOX fuel Fabrication
lxxxviii. Ibid.
lxxxix. The list of problem pits, like the list of weapons with disassembly
problems, seems to be dominated by LLNL designs. Three of the four pit types
requiring cleaning are LLNL designs, as is the most problematic pit, the W-48.
The only remaining weapons systems to dismantle under START I are LLNL
designs-the W79, the W56, which have both been problematic programs.
xc. Pantex Work Authorization Directives.
Fiscal Year 2000.
xci. Rocky Flats Safety Analysis Report for the AL-R8. 1990.
xcii. Khalil, Nazir, Bill Bish, and Ken Franklin. 1998. Process development implementation plan for pits,
LA-UR-98-5047. Page 2.
xciii. Sun-Woo, A.J., M.A. Brooks, and J.E. Kervin. 1995. Characterization of Stainless Steel 304 Tubing.
UCRL-ID-122234. October 16, 1995.
xciv. Mason and Hanger Corporation. 2000. Pantex
Pit Management Plan.
xcv. Khail, et al. Process development
implementation plan for pits.
xcvi. Stockpile Stewardship Enhanced
Surveillance Program. 1998.
xcvii. The unclassified version of the report can be downloaded in the “Public
Documents” section at http://www.dp.doe.gov.
xcviii. Commission on Maintaining United States Nuclear Weapons Expertise. Report to the Congress and Secretary of Energy
Pursuant to the National Defense Authorization Acts of 1997 and 1998. March 1,
1999
xcix. Savannah River Site Strategic Plan. http://www.srs.gov
c. Ibid.
ci. Rudisill, T.S. and M.L. Crowder. 1999. Characterization
of d Phase Plutonium Metal WSRC-TR-99-00448. Westinghouse Savannah
River Company
cii. Ibid.
ciii. Collins, Susan, and Henry Randolph. 1997. Gas Pycnometry for Density Determination of Plutonium Parts.
Westinghouse Savannah River Company. WSRC-MS-97-00636. Document prepared for
the 21st Aging, Compatibility, and Stockpile Stewardship Conference,
Albuquerque, NM. 9/30/97 to 10/2/97.
civ. Hart, Mark. M, Warren Wood, and J. David Olivas. Plutonioum Pit Manufacturing and Unit Process Separation
Options for Rapid Reconstitution. A Joint Position Paper of LLNL
and LANL. September 6, 1996. .
Over
the past few years, the dismantlement of excess nuclear warheads has left the
United States and Russia with large stocks of plutonium and highly enriched
uranium (HEU). These surpluses have re-ignited the debates around the world
about the use of plutonium as an energy source and provided new arguments for
continued assistance to on-going plutonium projects. This article reviews the
basic facts regarding plutonium use and provides some cost and technical
analysis of the issue.
Uranium and plutonium resource basics For
all practical purposes, uranium-235 is the only naturally-occurring fissile
material (one that can sustain a chain reaction and can fuel nuclear
reactors). However, uranium-235 makes up only about 0.7 percent of natural
uranium ore. Almost all the rest is another isotope, uranium-238, which
cannot sustain a chain reaction. But
although uranium-238 is not a fissile material, it can be converted into
fissile plutonium-239 in a nuclear reactor. This property has led nuclear
proponents to see uranium-238 as the key to the long-term future of nuclear
energy. In fact, reactors can be designed so that they produce more fissile
material from uranium-238 in the form of plutonium than they consume in the
course of power production. Such reactors have come to be called
"breeder reactors" and uranium-238 a "fertile" material.
Promoters of nuclear power have used the expression "magical energy
source" to describe a breeder reactor electricity production system
because the amount of fuel at the end of production would be greater than at
the beginning.1 In
the 1950s and 1960s, uranium was thought to be a very scarce resource.
Scientists realized that uranium resource requirements for a power system
based on breeder reactors would be far lower than for one based on
once-through use of uranium. For instance, the amount of natural uranium
needed over the life of a 1,000 megawatt 2 power plant with a
light water reactor (LWR-the most common nuclear reactor), is roughly 4,000
metric tons. By contrast, only about 40 metric tons are required for a
breeder reactor of the same size. This hundred-fold theoretical reduction in
resource requirements convinced proponents of nuclear power that breeder
reactors, along with the recovery of plutonium from irradiated reactor fuel
(reprocessing), would be at the heart of the magical nuclear energy future,
when nuclear power would be "too cheap to meter."3 At
that time, projections of nuclear power use were very high. In the early
1970s, the U.S. expected an installed nuclear capacity by the year 2000 of
1,000,000 megawatts. However, U.S. capacity is now only 10% of those
projections (about 100,000 megawatts) and will not increase by the year 2000
(see Table 3
for additional data). Nuclear Power and its
Role in Global Electricity and Energy
compiled
by Anita Seth
Theoretical
arguments in favor of breeder reactors still provide inspiration to nuclear establishments
all over the world. But technical, economic, political, environmental, and
military realities have all combined to make a plutonium-based energy system
economically impractical, environmentally dangerous, diplomatically
difficult, and militarily risky. Technical and economic complications Discussion
in this article focuses on the sodium-cooled breeder reactor (also called a
fast neutron reactor)-the main breeder reactor design that has been
developed. Tens of billions of dollars have been spent on research,
development, and demonstration of this technology in a number of countries,
including the United States, Russia, France, Britain, India, Japan, and
Germany. But the technology has not yet reached the commercial stage of even
moderately reliable power production and breeding of fuel. Breeder reactors
total a capacity of roughly 2,600 megawatts, which is only 0.8 percent of the
world's nuclear power capacity of about 340,000 megawatts (see pie chart).
In
turn, nuclear power plants account for 12 percent of the world's total
electrical capacity. Not only have "breeder" reactors produced only
a miniscule fraction of nuclear electricity; they have also failed to produce
a significant amount of net fissile material. Indeed, it is possible that
"breeder" reactors have so far been net consumers of fissile
material. Almost
half of the world's breeder reactor capacity is in a single reactor, the
Superphčnix in France, which has faced serious operating problems and is not
currently run as a breeder reactor. Rather, it is now a net burner of fissile
material, used mainly as a research facility for studying the fission of
plutonium and other similar elements called actinides. Another 10 percent of
breeder capacity is in the 280-megawatt Monju reactor in Japan, which had an
accident in December 1995, only eight months after its start up. (See graphic
below.)
Most
breeder reactors outside of France and Japan have operated on uranium fuel
rather than the more difficult plutonium fuel. Russia's BN600 sodium-cooled
reactor has been fueled primarily with highly enriched uranium and the BN350
in Kazakhstan now runs on medium-enriched uranium. A
number of problems have plagued the design and operation of breeder reactors:
Most breeder reactor programs
are now suspended or stopped due to the high capital costs and operating
problems discussed above. They have been abandoned or cut back to a low-level
research stage in the United States, Germany, and Britain. The Japanese
program has had a severe setback due to the December 1995 sodium-leak
accident at the Monju plant. The plant is not expected to be on line for
several years, if ever. There are no current plans for new breeder reactors
in France. Britain and Germany have pulled out of the European Breeder
Reactor project. India's program has so far produced only a small pilot
plant. Russian plans for breeder reactors are stalled for lack of money. The expense and technical difficulties
of breeder reactors, reprocessing, and plutonium fuel fabrication have led to
far higher net costs for breeder reactors than for reactors that load only
uranium as a fuel. Moreover, uranium is far more abundant than was presumed
in the 1950s and 1960s. Instead of rising, uranium prices have, on the
average, declined in real terms over the last several decades ( table below).
Furthermore, in the past ten
years, spot market prices (the open market price at any given time) have been
significantly lower than contract prices. For instance, in 1990 spot prices
were about $30 per kilogram of uranium (in 1995 dollars)-just half of the
contract price. In the past couple of years spot prices have ranged between
$20 and $40 per kilogram. Low uranium prices are also partly due to reduced
demand because the number of nuclear power reactors built has been far fewer
than projected. Value and cost of plutonium While electricity systems based
on breeder reactors have not been built, it is still possible to use
plutonium as a fuel in light water and other power reactors not designed to
breed plutonium. In any case, about one-fourth to one-third of the energy in
an LWR is derived from plutonium created in the course of reactor operation
from the uranium-238 in the fuel rods. Further, the spent fuel rods from LWRs
typically contain about 0.7 percent fissile isotopes of plutonium. This
plutonium, while far less than the amount of fissile material used in the
reactor, can be re-extracted for use as fuel. However, most reactors are not
designed to operate on pure plutonium. The total amount of fissile material
(uranium-235 plus fissile isotopes of plutonium) must be kept below the
design level -- in the vicinity of five percent for most LWRs. The plutonium
is put into oxide form, mixed with depleted uranium oxide (mainly uranium-238
with about 0.2 percent uranium-235) to make a mixed oxide fuel ("MOX
fuel"). Thus, it would appear that even without breeder reactors,
plutonium can be useful as a nuclear reactor fuel. While this argument is
theoretically correct from the point of view of physics, it fails on economic
grounds. To determine a practical economic value for plutonium, we must take
into account the costs of processing and fabricating it into usable fuel and
compare them to the costs of other fuels. The most detailed, recent
independent analysis done on this subject was a study of reactor options for
plutonium disposition published by the U.S. National Academy of Sciences
(NAS) in 1995. The NAS report estimated the
cost of processing and fabricating low enriched uranium oxide reactor fuel
(4.4 percent enrichment) at about $1,400 per kilogram in 1992 dollars,
assuming a natural uranium price of $55 per kilogram. The costs of MOX fuel
fabrication, assuming that the plutonium was free (that is, obtained as
surplus from the nuclear weapons program), would be about $1,900 per kilogram
in 1992 dollars, exclusive of taxes and insurance. 4 The higher
cost of MOX means that annual fuel costs for a full MOX core would be
approximately $15 million more than uranium fuel per year for a 1,000
megawatt reactor, or about $450 million over its operating life (in 1992
dollars), even if the plutonium were free. This amounts to about $500 millon
in 1995 dollars. Further, the costs of disposing of MOX spent fuel are likely
to be higher than those for uranium spent fuel because the MOX spent fuel
will be more radioactive and contain two to three times more residual
plutonium than uranium spent fuel. It is clear that so long as
uranium prices are relatively low, the use of MOX fuel is uneconomical even
under the most favorable circumstances: when the plutonium itself is free and
uranium is assumed to be more expensive than current spot market prices. The
cost difference is even greater when the cost of reprocessing is taken into
account, because reprocessing would add hundreds of millions of dollars to
lifetime fuel costs for each reactor. As the NAS pointed out in a 1994
study, the fact that plutonium has a fuel value in physical terms does not
make it economically practical. The oil present in shale rock also has a
physical fuel value. It is the cost of extracting oil from shale relative to
petroleum in oil fields that precludes oil shale, like plutonium, from having
an economic value as a fuel. In addition, plutonium poses some
proliferation liability which, although difficult to quantify, is a serious
cost. Proliferation Dangers Although civilian plutonium has
a different isotopic composition from plutonium that has been produced for
weapons, it can be used to make a nuclear explosive, as demonstrated in a
successful 1962 test by the United States Atomic Energy Commission. Continued
reprocessing and use of plutonium pose a two-fold proliferation danger.
First, growing stockpiles of commercial separated plutonium undermine
disarmament commitments under international treaties. Even if carried out for
commercial reasons, reprocessing of plutonium can be perceived as simply
adding to weapons-usable materials stockpiles. In the short-term, this could
undermine effective global negotiations on a fissile material cut-off, and in
the long-term, the Non-Proliferation Treaty, in which, under Article VI,
signatories commit to "pursue negotiations in good faith on effective
measures relating to the cessation of the arms race at an early date and to
nuclear disarmament . . ." Second is the danger of
plutonium being diverted to a black market. The fuel value of plutonium is
determined by the price of uranium. Assuming a price of $40 per kilogram of
natural uranium, uranium-235 is worth about $5,600 per kilogram. Since the
energy per fission from plutonium-239 and uranium-235 is about the same, the
theoretical fuel value of fissile plutonium can be put at $5,600 per
kilogram. Reactor-grade plutonium also contains non-fissile isotopes,
reducing its value to about $4,400 per kilogram. 5 Six to ten
kilograms of reactor-grade plutonium would suffice to make a nuclear bomb,
making the fuel value of one bomb's worth of plutonium between $26,400 and
$44,000. However, the value of the plutonium would undoubtedly be far greater
than this on a potential black market where the objective would be to make a
weapon. The danger of plutonium diversion to a black market is particularly
acute in Russia where the weakening of central control, combined with the
rise of organized crime and poor economic conditions heighten the chances of
diversion.
Long-term energy issues The economic facts regarding
plutonium are now so clear that they are not in serious dispute so far as short-
and medium-term energy issues are concerned. But supporters of plutonium as
an energy source cite long-term energy needs as a reason to create and
maintain an infrastructure for the use of plutonium. Current estimates of uranium
resources at $80 per kilogram of uranium (still well below the price at which
MOX fuel may be competitive) are estimated at about 3.3 million metric tons,
enough for about six or seven decades of once-through fuel use at present
levels of nuclear power production. These estimates do not take into account
the intense exploratory activity that accompanies real increases in prices.
The history of petroleum and natural gas exploration is instructive. The
price increases in 1973-74 resulted from production-limiting and price-fixing
policies adopted by the Organization of Oil Exporting Countries (OPEC).
However, the price jump spurred new exploration activity, and the number of
oil exporting countries and oil availability increased so substantially that
the real price of petroleum is lower today than it was in 1974. Uranium
prices have tended to decline in real terms (with the exception of a period
in the 1970s, when uranium prices followed the upward trend of oil prices),
and so current estimates of uranium resources may be biased downwards. Whatever one's views about the
future of nuclear power, it makes little sense to invest huge amounts of
money in using plutonium as a fuel today, when any potential economic use is
many decades away, at best. Plutonium use makes even less sense when viewed
in the context of scarce economic resources, which can be invested in areas
with better environmental and security characteristics and a higher return,
such as natural gas- or biomass-fueled power plants, natural gas-assisted
solar electricity generation, and improved efficiency of energy use. |
ENDNOTES
Disposing of Surplus U.S. Plutonium
The United States declared over 50 metric tons of plutonium surplus to defense needs.
The NNSA is pursuing a hybrid disposition strategy to eliminate the surplus.
- - - - - - - - -
- - - - - - - - - - - - - - -
DOE Press Release: R-97-001 January 14, 1997
DOE
ANNOUNCES DECISION ON THE STORAGE AND DISPOSITION OF SURPLUS NUCLEAR WEAPONS
MATERIALS
Secretary of Energy Hazel R. O’Leary today signed a Record of Decision finalizing a dual-track strategy to irreversibly dispose of the Nation’s surplus plutonium and to reduce from seven to three the number of sites where surplus nuclear weapons materials are stored. The strategy, first announced on December 9, 1996, allows for immobilizing plutonium in glass or ceramic forms and burning plutonium as mixed oxide fuel in existing reactors.
Today’s decision formally completes this phase of the program’s environmental review and is consistent with the preferred alternative identified in the Department’s final Environmental Impact Statement on Storage and Disposition of Nuclear Weapons Materials.
Secretary O’Leary said, "The Clinton administration believes that the dual-track approach for eliminating excess U.S. weapons plutonium stockpiles best serves our arms reduction and nonproliferation goals. Maintaining both the reactor and immobilization options will provide important insurance against possible difficulties with the implementation of either one and help ensure an early start to this important task. Furthermore, this approach will provide us the needed flexibility and leverage to work with Russia on the critical task of reducing Russian excess weapons plutonium stockpiles."
The Department of Energy (DOE) will consolidate the storage of plutonium by upgrading and expanding existing and planned facilities at the Pantex Pant in Texas and the Savannah River Site in South Carolina, and continue the storage of weapons-usable highly enriched uranium at DOE’s Y-12 Plant in Tennessee, in upgraded and consolidated facilities. After certain conditions are met, most plutonium now stored at the Rocky Flats Environmental Technology Site in Colorado will be moved to Pantex and the Savannah River Site. Plutonium currently stored at Hanford Site, the Idaho National Engineering Laboratory, and the Los Alamos National Laboratory will remain at those sites until disposition.
DOE will pursue a disposition approach that allows immobilization of surplus plutonium in glass or ceramic material for disposal in a geologic repository and burning of some of the surplus plutonium as mixed oxide (MOX) fuel in existing domestic, commercial reactors, with subsequent disposal of the spent fuel in a geologic repository. However, the Department has decided that at least 8 metric tons of surplus plutonium materials will be immobilized because they are not suitable for use in MOX fuel without extensive purification. The full extent to which either or both options are implemented will be determined by the results of technology demonstrations, additional environmental reviews and detailed cost proposals. The results of these efforts, as well as nonproliferation considerations and negotiations with Russia and other nations, will ultimately determine the timing and extent to which each technology is deployed.
Burning excess plutonium as MOX fuel in existing reactors would be consistent with U.S. nonproliferation policy because there would be no reprocessing and extraction of residual plutonium from the spent fuel. In addition, MOX fuel would be fabricated in a domestic, government-owned facility at a secure DOE site. The facility would be licensed and used only for the weapons plutonium disposition mission and would be shut down when this mission was complete.
The Department has also decided to retain the option of using MOX fuel in Canadian Deuterium Uranium (CANDU) reactors in Canada in the event a multilateral agreement to use CANDU reactors is negotiated among Russia, Canada and the United States.
Through these efforts, the President will be provided the basis and flexibility to begin disposition, either unilaterally as an example to Russia, or multilaterally or bilaterally with other nations. Proceeding in this way will serve as a strong statement of the United States’ commitment to nonproliferation and disarmament and encourage similar actions by Russia and other nations, and foster multilateral or bilateral disposition efforts and agreements.
- - - - - - - - - - - - - - - - -
- - - - - - - -
Both approaches convert the surplus plutonium to the "spent fuel standard" so it can’t be used to make a nuclear bomb.
As
recommended by the National Academy of Sciences, weapon-grade plutonium is
converted to forms as inaccessible and unattractive for retrieval and weapons
use as the residual plutonium in spent fuel from commercial reactors. In this
form, the surplus plutonium cannot be used in nuclear weapons without
significant processing.
The NNSA plans to build three facilities at the Savannah River Site (SRS) in South Carolina to carry out the hybrid disposition strategy.
· Pit Disassembly and Conversion Facility;
Pit Disassembly and Conversion
About two-thirds of the
surplus U.S. weapon-grade plutonium exists in classified nuclear weapons
components called "pits".
Pits, whose designs are classified, are the core component of a nuclear weapon. Pits are comprised of plutonium, hermetically sealed within a metallic shell that, when imploded by high explosives, initiates a thermonuclear reaction
The NNSA plans to build a Pit Disassembly and Conversion Facility at the Savannah River Site. The facility will use the Advanced Retrieval and Integrated Extraction System (ARIES) process to:
University of California
scientists and engineers have developed ARIES, the Advanced Recovery and
Integrated Extraction System, at Los Alamos National Laboratory. This system
separates plutonium from nuclear weapons components. The plutonium is
declassified and packaged for future disposition.
ARIES exemplifies the commitment of the United States to remove 50 tons of
weapons-grade plutonium, as agreed to by United States President Bill Clinton
and Russian Federation President Boris Yeltsen on September 2, 1998.
Washington Group International is designing the facility. Design efforts are underway. In order to reduce the anticipated future year peak funding requirements, work on the pit disassembly and conversion facility is being delayed until the construction of the Mixed Oxide (MOX) Fuel Fabrication Facility is further along.
· MOX Fuel Fabrication Facility; and
Irradiation of Mixed Oxide Fuel
The NNSA will irradiate surplus U.S. weapon-grade plutonium converted from classified weapon "pits" and clean metal as mixed oxide (MOX) fuel in domestic commercial reactors.
The NNSA plans to build a MOX Fuel Fabrication Facility at the Savannah River Site. The facility will use commercial processes similar to ones used in European facilities. The U.S. facility will:
Each MOX fuel assembly is approximately 8 inches square and just over 13 feet long, and contains 264 fuel pins. Each MOX fuel assembly will contain about 20 kilograms of surplus weapon-grade plutonium, and weigh about 1,100 pounds. Each domestic reactor will hold up to 40 complete MOX fuel assemblies during an irradiation cycle.
A consortium of Duke, COGEMA, Stone & Webster (DCS), located in Charlotte, North Carolina, is designing the facility, and may also construct and operate the facility. The U.S. Nuclear Regulatory Commission will regulate the construction and operation of the facility.
Duke Power Company will irradiate the mixed oxide fuel assemblies in commercial reactor facilities in North Carolina and South Carolina. Revised operating licenses from the Nuclear Regulatory Commission are necessary in order to irradiate mixed oxide fuel.
· Plutonium Immobilization Facility.
Immobilization
The NNSA will immobilize surplus U.S. plutonium that exists as impure metal and oxides because these materials are unsuitable for irradiation as mixed oxide fuel without extensive purification.
The NNSA plans to build a Plutonium Immobilization Facility at the Savannah River Site (SRS). The facility will use a new process to:
The immobilization process is completed at the existing Defense Waste Processing Facility at the SRS, where molten high-level radioactive waste is poured into the canister to provide a radiation barrier for proliferation resistance.
Each
10-foot tall high-level waste canister will contain 28 steel cans, each
containing 20 ceramic plutonium pucks. About 1 kilogram of plutonium is inside
each steel can. When filled with vitrified high-level radioactive waste, each
canister will weigh close to 5,500 pounds
Research and development on immobilization is supported by Lawrence Livermore National Laboratory, the SRS, Clemson University, Argonne National Laboratory, and the Pacific Northwest National Laboratory.
In order to reduce the anticipated future year peak funding requirements, work on immobilization is being suspended and will be resumed when construction of the Mixed Oxide (MOX) Fuel Fabrication Facility and the Pit Disassembly and Conversion Facility are further along.
Surplus plutonium at various sites will be transported to the SRS for disposition.
|
|
|
|
Working with Russia to Dispose of Surplus Russian Plutonium
|
|
|
|
Russia has declared
approximately 50 metric tons of plutonium
surplus to their defense needs.
Russian President Boris Yeltsin made the first official declaration of excess Russian fissile materials in 1997, stating that up to 50 metric tons of weapons plutonium and up to 500 metric tons of highly enriched uranium excess to Russian defense needs.
Russia intends to dispose of their surplus plutonium in reactors by irradiating mixed oxide (MOX) fuel. They may immobilize small amounts that are unsuitable for use in reactors.
In 1998, the United States and Russia signed a Scientific and Technical
Cooperation Agreement to conduct tests and demonstrations of plutonium
disposition technologies.
-
- - - - - - - - - - - - - - - - - - - -
Scientific and Technical Cooperation Agreement
Signed by Vice President Gore and Prime Minister Kiriyenko in July 1998.
- - - - - - - - - - - - - - - - -
Initial efforts focused on:
GOSATOMNADZOR (GAN) is the Federal Nuclear and Radiation Safety Authority of Russia. The Department of Energy is helping GAN develop the regulatory infrastructure required for licensing the design, construction, testing and operation of Russian Federation nuclear facilities for surplus weapons plutonium disposition.
Specific help is provided to develop nuclear regulations and safety standards needed to license new or modified facilities for disposition, and to support review of license applications and granting of licenses and permits for the disposition facilities.
The National Nuclear Security Administration is supporting
research and development of advanced
reactors that might provide additional surplus weapon plutonium disposition
capacity in Russia.
Advanced Reactors
The Gas Turbine-Modular Helium Reactor (GT-MHR) technology project could provide additional surplus weapon plutonium disposition capacity in Russia.
General Atomics worked with the Ministry of the Russian Federation of Atomic Energy (Minatom), Framatome from France, and Fuji Electric Corporation from Japan, to produce a conceptual design for a GT-MHR that would be used for plutonium disposition.
General Atomics and the Oak Ridge National Laboratory now provide technical support to many Russian organizations to design a plutonium -burning reactor for Seversk such as the Gas Turbine Modular Helium Reactor.
The GT-MHR project was integrated into the existing framework of the joint Scientific and Technical Cooperation Agreement.
The United States and Russia recently concluded a bilateral agreement on plutonium disposition. Under the agreement, both the United States and Russia will proceed with roughly parallel programs to dispose of 68 metric tons of surplus weapon-grade plutonium.
- - - - - - - - - - - - - - - - -
- - -
White House Press Release
September 1, 2000
VICE
PRESIDENT AL GORE SIGNS U. S. - RUSSIA PLUTONIUM MANAGEMENT AND DISPOSITION
AGREEMENT
Washington, D.C. – Vice
President Gore signed today the United States-Russian Federation Agreement for
irreversibly transforming excess weapons plutonium into forms unusable for
weapons, announced by President Clinton and President Putin at the June 4
Moscow Summit. With this act and Prime Minister Kasyanov’s signature, the
Agreement shall be applied as of today’s date. This accomplishment advances the
critical task of reducing stockpiles of excess weapons plutonium and
contributes to key arms control and non-proliferation objectives.
The Agreement requires that 68
metric tons of weapons-grade plutonium, 34 tons for each Party, be disposed.
This is enough plutonium for thousands of nuclear weapons. It will be disposed
by irradiating it as fuel in reactors or by immobilizing it with high-level
radioactive waste, rendering it suitable for geologic disposal. Implementation
will require the construction of new industrial-scale facilities to convert and
fabricate this plutonium into fuel in both countries, and to immobilize a
portion of the U.S. material. The Agreement sets 2007 as the target date to
begin operating such facilities with a minimum disposition goal of 2 metric
tons per year and an obligation to seek to at least double that rate.
The Agreement establishes the
goals, time lines, and conditions for ensuring that this plutonium can never
again be used for weapons or any other military purposes. Both the process and
the end products will be subject to monitoring and, thus, transparent. The
Agreement bans reprocessing any of this plutonium prior to the disposition of
all 34 metric tons. Reprocessing thereafter must be under mutual-agreed,
effective monitoring measures. Plutonium immobilization under the program must
never be separated from the immobilized forms. The Agreement allows plutonium
that may be designated as excess to defense needs in the future to come under
the surplus program.
As the Presidents’ Joint
Statement noted, the Agreement will enable new cooperation to go forward
between the United States and the Russian Federation. Thanks to the leadership
of Senator Domenici and others in the U.S. Congress, $200 million has already
been appropriated to help implement the Russian program.
Other G-8 countries have
strongly endorsed and advanced this cooperation. The Untied States and Russian
Federation have urged the G-8 leaders at their recent summit to accelerate this
cooperation by directing development of necessary multilateral arrangements and
an international financing process for assisting Russia’s program. The plan
will consider both public and private sector financing mechanisms.
Also present to today’s signing
was Michael Guhin, U.S. negotiator.
Bilateral Agreement on Plutonium Disposition
A bilateral agreement on plutonium disposition calls for the United States and Russia to irreversibly dispose of surplus weapon-grade plutonium. Each country will:
Plutonium disposition in Russia requires substantial financial assistance from the international community. An international financing plan and additional multi-lateral arrangements are being developed for the Genoa 2001 G-8 Summit. The U.S. Department of State will lead U.S. efforts to finalize the plan. Several nations have already pledged significant resources for the plutonium disposition effort in Russia.
With the signing of the bilateral agreement on Plutonium disposition, Russia and the United States will accelerate and expand ongoing plutonium disposition research, development, and demonstration work under the Joint U.S.-Russian Scientific and Technical Cooperation Agreement.
Fabrication and Use of Mixed Oxide Fuel
The United States, France, Germany, Japan and others are collaborating with Russia on developing mixed oxide (MOX) fuel fabrication processes to irradiate surplus Russian weapon-grade plutonium.
o Adapting proven European MOX fabrication experience to Russian fuel designs;
o Assessing feasibility of either pelletized fuel fabricated at the Mayak Production Association in Ozersk or vibro-compacted fuel fabricated at the Research Institute of Atomic Reactors (RIAR) in Dmitrovgrad;
o Working with AIDA-MOX on a parallel development effort with France and Germany; and
o Fabricating test fuel for irradiation in a research reactor and lead test assemblies.
Russia will build a mixed oxide fuel fabrication facility at either the Mayak Production Association in Ozersk or at the Mining and Chemical Combine in Zheleznogorsk (the closed city formerly known as Krasnoyarsk-26).
Rosenergoatom, the Russian utility that operates nuclear power reactors, is involved in the effort as the ultimate user of the MOX fuel. Final fabrication and use of the fuel is subject to approval by Gosatomnadzor, which will license the use of MOX fuel in Russian reactors.
Russia will use two types of existing nuclear power plants to irradiate mixed oxide fuel:
VVER is the Russian version of the Pressurized Water Reactor (PWR). There are 3 standard designs - two 6 loop- 440 Megawatt [440-230 (older) and 440-213 (newer)] and 4 loop-1000 Megawatt output designs. As with PWRs, annual refuelings are conducted with the plant shutdown. The VVER-1000 units at Balakovo and Kalinin Nuclear Power Plants will be used in the program.
Balakovo Nuclear Power Plant
Balakovo NPP, 1997
|
||||
|
Unit 1 |
Unit 2 |
Unit 3 |
Unit 4 |
Type of reactor |
VVER-1000 |
VVER-1000 |
VVER-1000 |
VVER-1000 |
Power, MWe |
1000 |
1000 |
1000 |
1000 |
First Power |
28.12.85 |
08.10.87 |
24.12.88 |
11.04.93 |
Generated electrical power, mln kW·h |
5004,2 |
4302,2 |
2209,6 |
4938,0 |
In-house requirements, % |
5,65 |
7,18 |
8,08 |
6,17 |
Reactor operational time, days |
242 |
257 |
141 |
276 |
Reactor operational time, effective days |
209 |
179 |
92 |
206 |
Load Factor, % |
57,12 |
49,11 |
25,22 |
56,38 |
Kalinin NPP, 1997 |
||
|
Unit 1 |
Unit 2 |
Type of reactor |
VVER-1000 |
VVER-1000 |
Power, MWe |
1000 |
1000 |
First Power |
09.05.84 |
03.12.86 |
Generated electrical power, mln kW·h |
5496,2 |
4138,4 |
In-house requirements, % |
5,61 |
6,38 |
Reactor operational time, days |
258 |
255 |
Reactor operational time, effective days |
229 |
172 |
Load Factor, % |
62,74 |
47,26 |
Beloyarsk NPP, 1997 |
|
|
Unit 3 |
Type of reactor |
BN-600 |
Power, MWe |
600 |
First Power |
08.04.80 |
Generated electrical power, mln kW·h |
3835,4 |
In-house requirements, % |
7,55 |
Reactor operational time, days |
278 |
Reactor operational time, effective days |
266 |
Load Factor, % |
72,99 |