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REACTOR
GRADE PLUTONIUM AND NUCLEAR WEAPONS
Summary:
Reactor grade plutonium can be used in nuclear weapons, albeit the case
that weapons manufacture using reactor grade plutonium is more
difficult and dangerous compared to weapon grade plutonium. In addition
to the potential to use plutonium produced in a normal power reactor
operating cycle, there is the option of using civil power or research
reactors to irradiate uranium for a much shorter period of time to
produce plutonium ideally suited to weapons manufacture.
A standard
nuclear power reactor (1000 MWe LWR) produces about 290 kilograms of
plutonium each year. Hundreds of tonnes of plutonium have been produced
in power reactors (and to a lesser extent research reactors), hence the
importance of the debate over the use of reactor grade plutonium in
weapons.
Plutonium
grades
For weapons
manufacture, the ideal plutonium contains a very high proportion of
plutonium-239. As neutron irradiation of uranium-238 proceeds, the
greater the quantity of isotopes such as plutonium-240, plutonium-241,
plutonium-242 and americium-241, and the greater the quantity of
plutonium-238 formed (indirectly) from uranium-235. These unwanted
isotopes make it more difficult and dangerous to produce nuclear
weapons.
Definitions of
plutonium usually refer to the level of the unwanted plutonium-240
isotope:
* Weapon grade
plutonium contains less than 7% plutonium-240. (A sub-category - super
grade plutonium - contains 2-3% plutonium-240 or less.)
* Fuel grade
plutonium contains 7-18% plutonium-240
* Reactor grade
plutonium contains over 18% plutonium-240.
Although
somewhat imprecise, it is also useful to distinguish low burn-up
plutonium (high in plutonium-239, including weapon grade plutonium and
some or all fuel grade plutonium) from high burn-up plutonium
(including reactor grade plutonium and possibly some fuel grade
plutonium).
According to
the Uranium Information Centre (2002), plutonium in spent fuel removed
from a commercial power reactor (burn-up of 42 GWd/t) consists of about
55% Pu-239, 23% Pu-240, 12% Pu-241 and lesser quantities of the other
isotopes, including 2% of Pu-238 which is the main source of heat and
radioactivity. Elsewhere, the Uranium Information Centre (2004) states
that plutonium contained in spent fuel elements is typically about
60-70% Pu-239. Carlson et al. (1997) from the Australian Safeguards and
Non-proliferation Office note that current commercial light- and
heavy-water reactors contains around 50-65% Pu-239.
Weapon
grade plutonium and fuel grade plutonium from power reactors
Nuclear power
reactors can of course be operated on a much shorter than usual
irradiation cycle in order to produce large quantities of weapon grade
and/or fuel grade plutonium for use in weapons. It is sometimes argued
that short irradiation times would adversely effect the commercial
operation of a power reactor, but that would probably be of minimal
concern to a would-be proliferator.
During a normal
reactor operating cycle (in which fuel typically remains in the reactor
for 3-4 years), a large majority of the plutonium formed is reactor
grade. However, the grade of the plutonium varies depending on the
position of the particular fuel elements in the reactor. Carlson et al.
(1997) note that: "Even though fuel assemblies are moved around during
refuelling, some parts of fuel rods will have a plutonium isotope
composition closer to that of [weapon grade plutonium]."
Weapon grade
plutonium can be inadvertently produced in power reactors. Carlson et
al. (1997) cite the example of leaking fuel rods in a reactor in the US
in the 1970s, leading the utility to discharge the entire initial
reactor core containing a few hundred kilograms of plutonium with
89-95% Pu-239.
Fuel grade
plutonium is produced in some nuclear reactors. It is often produced in
tritium production reactors, and can also be produced in power reactors
in initial core loads and in damaged fuel discharged from the reactor
earlier than normal (Carlson et al., 1997).
Carlson et al.
(1997) note the normal operation of on-load refuelling reactors (eg
certain gas-graphite and heavy water reactors) can result in some low
burn-up plutonium.
The development
of fast breeder technology has the potential to result in large-scale
production of weapon grade plutonium (Carlson et al., 1997).
Carlson et al.
(1997) note that at least five tonnes of civil plutonium under IAEA
safeguards is in the upper range of fuel grade plutonium or weapon
grade plutonium.
Reactor
grade plutonium
With the
exception of a few contrarians (discussed below), there is general
agreement that reactor grade plutonium can be used to produce weapons,
though the process is more difficult and dangerous than the use of
weapon grade plutonium (see Gorwitz, 1998 for discussion and
references).
The
difficulties associated with the use of reactor grade plutonium are as
follows.
If the starting
point is spent reactor fuel, the hazards of managing that spent fuel
must be addressed and there must be the capacity to separate plutonium
from spent fuel. Spent fuel from power reactors running on a normal
operating cycle will be considerably more radioactive and much hotter
than low burn-up spent fuel. Thus the high burn-up spent fuel (and the
separated reactor grade plutonium) are more hazardous - though it is
not difficult to envisage scenarios whereby proliferators place little
emphasis on worker safety. It may also be more time consuming and
expensive to separate reactor grade plutonium than separation from low
burn-up spent fuel.
Weapons with
reactor grade plutonium are likely to be inferior in relation to
reliability and yield when compared to weapon grade plutonium. Emission
of fission neutrons from plutonium-240 may begin the chain reaction too
early to achieve full explosive yield. However, devastating nuclear
weapons could still be produced. Radiation and heat levels could
diminish reliability through their effects on weapons components such
as high explosives and electronics.
According to
Leventhal and Dolley (1999), the high rate of neutron generation from
plutonium-240 can be turned to advantage as it "eliminates the need to
include a neutron initiator in the weapon, considerably simplifying the
task of designing and producing such a weapon".
A greater
quantity of reactor grade plutonium may be required to produce a weapon
of similar yield, or conversely there will be a lower yield for reactor
grade plutonium compared to a similar amount of weapon grade plutonium.
Storage life
would be adversely affected by the difficulties associated with reactor
grade plutonium.
The
majority view
A strong
majority of informed opinion holds that reactor grade plutonium can
indeed be used in nuclear weapons despite the above-mentioned problems.
A report from
the US Department of Energy (1997) puts the following view:
"Virtually any
combination of plutonium isotopes - the different forms of an element
having different numbers of neutrons in their nuclei - can be used to
make a nuclear weapon. ...
The only
isotopic mix of plutonium which cannot realistically be used for
nuclear weapons is nearly pure plutonium-238, which generates so much
heat that the weapon would not be stable. ...
At the lowest
level of sophistication, a potential proliferating state or subnational
group using designs and technologies no more sophisticated than those
used in first-generation nuclear weapons could build a nuclear weapon
from reactor-grade plutonium that would have an assured, reliable yield
of one or a few kilotons (and a probable yield significantly higher
than that). At the other end of the spectrum, advanced nuclear weapon
states such as the United States and Russia, using modern designs,
could produce weapons from reactor-grade plutonium having reliable
explosive yields, weight, and other characteristics generally
comparable to those of weapons made from weapons-grade plutonium. ...
"Proliferating
states using designs of intermediate sophistication could produce
weapons with assured yields substantially higher than the kiloton-range
possible with a simple, first-generation nuclear device. ...
"The
disadvantage of reactor-grade plutonium is not so much in the
effectiveness of the nuclear weapons that can be made from it as in the
increased complexity in designing, fabricating, and handling them. The
possibility that either a state or a sub-national group would choose to
use reactor-grade plutonium, should sufficient stocks of weapon-grade
plutonium not be readily available, cannot be discounted. In short,
reactor-grade plutonium is weapons-usable, whether by unsophisticated
proliferators or by advanced nuclear weapon states."
An expert
committee drawn from the major US nuclear laboratories concludes its
report by noting: "Although weapons-grade plutonium is preferable for
the development and fabrication of nuclear weapons and nuclear
explosive devices, reactor grade plutonium can be used." (Hinton et
al., 1996.)
According to
Robert Seldon (1976), of the Lawrence Livermore Laboratory: "All
plutonium can be used directly in nuclear explosives. The concept of
... plutonium which is not suitable for explosives is fallacious. A
high content of the plutonium 240 isotope (reactor-grade plutonium) is
a complication, but not a preventative."
According to J.
Carson Mark (1993), former director of the Theoretical Division at Los
Alamos National Laboratory: "Reactor-grade plutonium with any level of
irradiation is a potentially explosive material. The difficulties of
developing an effective design of the most straightforward type are not
appreciably greater with reactor-grade plutonium than with those that
have to be met for the use of weapons-grade plutonium."
According to
Matthew Bunn (1997), chair of the US National Academy of Sciences'
analysis of options for the disposal of plutonium removed from nuclear
weapons: "For an unsophisticated proliferator, making a crude bomb with
a reliable, assured yield of a kiloton or more - and hence a
destructive radius about one-third to one-half that of the Hiroshima
bomb - from reactor-grade plutonium would require no more
sophistication than making a bomb from weapon-grade plutonium. And
major weapon states like the United States and Russia could, if they
chose to do so, make bombs with reactor-grade plutonium with yield,
weight, and reliability characteristics similar to those made from
weapon-grade plutonium. That they have not chosen to do so in the past
has to do with convenience and a desire to avoid radiation doses to
workers and military personnel, not the difficulty of accomplishing the
job. Indeed, one Russian weapon-designer who has focused on this issue
in detail criticized the information declassified by the US Department
of Energy for failing to point out that in some respects if would
actually be easier for an unsophisticated proliferator to make a bomb
from reactor-grade plutonium (as no neutron generator would be
required)."
According to
Prof. Marvin Miller, from the MIT Defense and Arms Control Studies
Program: "[W]ith an amount on the order of 10 kilograms, it is now
possible for a small group, conceivably even a single 'nuclear
unibomber' working alone, to 'reinvent' a simplified version of the
Trinity bomb in which the use of reactor-grade rather than weapon-grade
plutonium is an advantage." (Quoted in Dolley, 1997.)
According to
the Office of Arms Control and Nonproliferation, US Department of
Energy: "There is clear scientific evidence behind the assertion that
nuclear weapons can be made from weapons-grade and reactor-grade
plutonium." (Quoted in Dolley, 1997.)
According to
Steve Fetter (1999) from Stanford University's Centre for International
Security and Cooperation, "All nuclear fuel cycles involve fuels that
contain weapon-usable materials that can be obtained through a
relatively straightforward chemical separation process. ... In fact,
any group that could make a nuclear explosive with weapon-grade
plutonium would be able to make an effective device with reactor-grade
plutonium. ... The main alternative to the once-through cycle involves
the separation and recycling of the plutonium and uranium in the spent
fuel. Not only is separation and recycle more expensive, it increases
greatly the opportunities for theft and diversion of plutonium."
According to
Hans Blix, then IAEA Director General: "On the basis of advice provided
to it by its Member States and by the Standing Advisory Group on
Safeguards Implementation (SAGSI), the Agency considers high burn-up
reactor-grade plutonium and in general plutonium of any isotopic
composition with the exception of plutonium containing more than 80
percent Pu-238 to be capable of use in a nuclear explosive device.
There is no debate on the matter in the Agency's Department of
Safeguards." (Blix, 1990; see also Anon., 1990).
The IAEA
Department of Safeguards has stated that "even highly burned
reactor-grade plutonium can be used for the manufacture of nuclear
weapons capable of very substantial explosive yields." (Shea and
Chitumbo, 1993.)
With the
exception of plutonium comprising 80% or more of the isotope
plutonium-238, all plutonium is defined by the IAEA as a "direct use"
material, that is, "nuclear material that can be used for the
manufacture of nuclear explosives components without transmutation or
further enrichment", and is subject to equal levels of safeguards.
Nuclear
tests using reactor grade or fuel grade plutonium
The US
government has acknowledged that a successful test using 'reactor
grade' plutonium was carried out at the Nevada Test Site in 1962 (US
Department of Energy, 1994). The information was declassified in July
1977. The yield of the blast was less than 20 kilotons.
The US
Department of Energy (1994) states: "The test confirmed that
reactor-grade plutonium could be used to make a nuclear explosive. ...
The United States maintains an extensive nuclear test data base and
predictive capabilities. This information, combined with the results of
this low yield test, reveals that weapons can be constructed with
reactor-grade plutonium."
The US
Department of Energy (1994) makes the connection to current debates
over reprocessing, stating that: "The release of additional information
was deemed important to enhance public awareness of nuclear
proliferation issues associated with reactor-grade plutonium that can
be separated during reprocessing of spent commercial reactor fuel."
The exact
isotopic composition of the plutonium used in the 1962 test remains
classified. It has been suggested (e.g. by Carlson et al., 1997) that
because of changing classification systems, the plutonium used in the
1962 test may have been fuel grade plutonium using current
classifications. De Volpi (1996) is sceptical that the plutonium used
in 1962 the test would be classed as reactor grade using current
classifications, but states that it was below weapon grade, i.e. it was
fuel grade plutonium.
Hore-Lacey from
the industry-funded Uranium Information Centre contends that the
isotopic composition of the plutonium used in the 1962 test "has not
been disclosed, but it was evidently about 90% Pu-239". However, there
is no compelling evidence to judge whether the test used reactor grade
plutonium or fuel grade plutonium.
Regardless of
the debate over the quality of the plutonium used in the 1962 test, and
the more general debate over the suitability of reactor grade plutonium
for weapons, it is worth noting again that civil power and research
reactors can certainly be used to produce weapon grade or fuel grade
plutonium simply by limiting the irradiation time.
India Today
reported in 1998 that one or more of the 1998 tests in India used
reactor grade plutonium (Anon., 1998).
(In Lorna Arnold's 'official' history of the British bomb tests in
Australia, titled "A very special relationship", and in other
literature such as De Volpi (1996), it is stated that one
of the two Totem nuclear tests at Emu Field in South Australia in 1953
used below-weapon-grade plutonium. However, measurements of Pu/Am
ratios at the bomb sites by Australian
nuclear physicists do not support the claim and the British have since
stated that the plan to use below-weapon-grade plutonium was abandoned
because it was not available in time for the test. The Pu/Am data is
presented in P.A. Burns et al., Health Physics 67, 1994, pp.226-232.)
Contrary
views
The
industry-funded Uranium Information Centre (2002) notes that a
significant proportion of Pu-240 would make a weapon "hazardous to the
bomb makers, as well as unreliable and unpredictable", that plutonium
for weapons is produced in dedicated production reactors usually
fuelled with natural uranium, and that: "This, coupled with the
application of international safeguards, effectively rules out the use
of commercial nuclear power plants."
In the same
paper, the Uranium Information Centre (2002) asserts that: "While of a
different order of magnitude to the fission occurring within a nuclear
reactor, Pu-240 has a relatively high rate of spontaneous fission with
consequent neutron emissions. This makes reactor-grade plutonium
entirely unsuitable for use in a bomb." The UIC refers to the
Australian Safeguards and Non-Proliferation Office (1998-99) in support
of that claim, though the ASNO material does not support such a strong
claim.
According to
Hore-Lacey (2003) from the UIC: "Due to spontaneous fission of Pu-240,
only a very low level of it is tolerable in material for making
weapons. Design and construction of nuclear explosives based on normal
reactor-grade plutonium would be difficult and unreliable, and has not
so far been done."
The UIC (2004)
states: "The only use for "reactor grade" plutonium is as a nuclear
fuel, after it is separated from the high-level wastes by reprocessing.
It is not and has never been used for weapons, due to the relatively
high rate of spontaneous fission and radiation from the heavier
isotopes such as Pu-240 making any such attempted use fraught with
great uncertainties."
Some of the
above statements for the UIC imply that it is impossible to use reactor
grade plutonium in weapons, but the available evidence does not support
that argument. The assertion that reactor grade plutonium has never
been used in weapons is, at best, questionable.
The Australian
Safeguards and Non-proliferation Office (ASNO) also makes the dubious
claim that there has been no "practical demonstration" of the use of
reactor grade plutonium in nuclear weapons. (ASNO, 1998-99.)
According to
Prof. Richard Broinowski (2003, p.276-277): "It is ... disingenuous to
argue, as John Carlson, ASNO's Director-General repeatedly does, that
Australian-obligated plutonium ... cannot be used in nuclear devices.
Certainly, a power reactor in normal operating mode produces irradiated
fuel richer in Pu-240 and Pu-241 than weapons-grade Pu-239. But as has
been widely and authoritatively established, reactor-grade plutonium is
still fissionable in a nuclear weapon if its heat evolution is
carefully managed. Also, Pu-240 and Pu-241 can be refined back to
Pu-239 through conversion to plutonium hexafluoride (PuF6) and laser
treatment." (According to Gorwitz (1996), reactor grade plutonium can
be upgraded to fuel or weapon grade plutonium but the technology is
beyond the capability of all but the most advanced countries.)
Implications
The potentially
catastrophic implications of nuclear weapons proliferation demands that
a conservative approach be adopted to the question of reactor grade
plutonium. In other words, for the purposes of public policy it should
be assumed that reactor grade plutonium can be used to make nuclear
weapons and that the difficulties and dangers of so doing would pose
only a minimal deterrent. There are of course many related areas where
the importance of a conservative position is accepted - in relation to
the health effects of low-level radiation, for example.
Carlson et al.
(1997), from the Australian Safeguards and Non-Proliferation Office,
state: "The situation which arose with the DPRK highlights the fact
that production of separated weapons-grade material by a
non-nuclear-weapon State should not be accepted as a normal activity.
Even for nuclear-weapon States, the proposal for a convention on the
cut-off of production of fissile material for weapons purposes has
implications in this regard. A proscription on the production - or
separation - of plutonium at or near weapons-grade would be an
important confidence-building measure in support of the disarmament and
non-proliferation regime."
Applying the
conservative principle, ASNO's arguments ought to be extended to
include reactor grade plutonium. Its production should be minimised
(e.g. with a phase-out of nuclear power). Separation of any plutonium
from irradiated materials ought to proscribed immediately.
References
Anon., November
12, 1990, "Blix Says IAEA Does Not Dispute Utility of Reactor-Grade Pu
for Weapons," Nuclear Fuel, p.8.
Anon., October
10, 1998, "The H-Bomb", India Today.
Australian
Safeguards and Non-Proliferation Office, 1998-99, Annual Report,
pp.55-59. <www.uic.com.au/nip18.htm>
Blix, H.,
November 1, 1990, Letter to the Nuclear Control Institute, Washington
DC.
Broinowski,
Richard, 2003, "Fact or Fission? The Truth About Australia's Nuclear
Ambitions", Melbourne: Scribe.
Bunn, M., June
1997, paper presented at International Atomic Energy Agency Conference,
Vienna.
Carlson, J., J.
Bardsley, V. Bragin and J. Hill (Australian Safeguards and
Non-Proliferation Office), "Plutonium isotopics - non-proliferation and
safeguards issues", Paper presented to the IAEA Symposium on
International Safeguards, Vienna, Austria, 13-17 October, 1997,
<www.asno.dfat.gov.au/O_9705.html>
Carson Mark,
J., 1993, "Explosive Properties of Reactor-Grade Plutonium",
<ccnr.org/Findings_plute.html>.
De Volpi, Alex,
October 1996, "A Cover-up of Nuclear-Test Information", APS Forum on
Physics and Society, Vol. 25, No. 4.
<www.aps.org/units/fps/newsletters/1996/october/aoct96.cfm#a2>
Dolley, Steven,
March 28, 1997, Using warhead plutonium as reactor fuel does not make
it unusable in nuclear bombs, <www.nci.org/i/ib32897c.htm>.
Fetter, Steve,
1999, "Climate Change and the Transformation of World Energy Supply",
Stanford University - Centre for International Security and Cooperation
Report, <cisac.stanford.edu/publications/10228>.
Gorwitz, Mark,
1996, "The Plutonium Special Isotope Separation Program: An Open
Literature Analysis".
Gorwitz, Mark,
1998, "Foreign Assistance to Iran's Nuclear and Missile Programs",
<www.globalsecurity.org/wmd/library/report/1998/iran-fa.htm>. See
Appendix A and references.
Hinton, J.P.,
October 1996, "Proliferation Vulnerability", Red Team Report. Sandia
National Laboratories Publication, SAND 97-8203,
<www.ccnr.org/plute_sandia.html>.
Hore-Lacey,
Ian, 2003, Nuclear Electricity, Seventh Edition, Chapter 7, published
by Uranium Information Centre Ltd and World Nuclear Association,
<www.uic.com.au/ne.htm>.
Leventhal,
Paul, and Steven Dolley, (Nuclear Control Institute), 1999,
"Understanding Japan's Nuclear Transports: The Plutonium Context",
Presented to the Conference on Carriage of Ultrahazardous Radioactive
Cargo by Sea: Implications and Responses,
<www.nci.org/k-m/mmi.htm>.
Selden, R. W.,
1976, Reactor Plutonium and Nuclear Explosives, Lawrence Livermore
Laboratory, California.
Shea, T.E. and
K. Chitumbo, "Safeguarding Sensitive Nuclear Materials: Reinforced
Approaches", IAEA Bulletin, #3, 1993, p.23.
Uranium
Information Centre, 2002, "Plutonium", Nuclear Issues Briefing Paper
18, <www.uic.com.au/nip18.htm>.
Uranium
Information Centre, October 2004, "Safeguards to Prevent Nuclear
Proliferation", Nuclear Issues Briefing Paper 5,
<www.uic.com.au/nip05.htm>. (Accessed May 1, 2005.)
US Department
Energy, June 1994, Office of the Press Secretary, "Additional
Information Concerning Underground Nuclear Weapon Test of Reactor-Grade
Plutonium", DOE Facts (1994) 186-7. Reproduced on the US Office of
Scientific and Technical Information website,
<www.osti.gov/html/osti/opennet/document/press/pc29.html>. Also
available at: <www.ccnr.org/plute_bomb.html>.
US Department
of Energy, 1997, Office of Arms Control and Nonproliferation, January,
"Final Nonproliferation and Arms Control Assessment of Weapons-Usable
Fissile Material Storage and Excess Plutonium Disposition
Alternatives", Washington, DC: DOE, DOE/NN-0007, pp.37-39.
<www.ccnr.org/plute.html>.
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