Uranium: Its Uses and Hazards

Some of the terms used in this factsheet are defined in IEER's on-line glossary.

 

 

Uranium Radiation Properties

(last updated 1 Sep 2000)

Contents:

• Introduction · Decay Series
• Uranium Ore / Waste Rock
• Uranium In-situ Leach Solution
• Radon
• Uranium Ore Concentrate (U₃O₈)
• Uranium Mill Tailings
• HWR Fuel (natural UO₂)
• Magnox Fuel (natural U metal)
• Uranium Hexafluoride (UF₆): enriched · depleted
• LWR Fuel (enriched UO₂)
• Depleted Uranium Metal
• Depleted Uranium Oxide (UO₂ or U₃O₈)
• References

> see also:

• Unit Converter
• Uranium Decay Calculator
• Uranium Toxicity
• Uranium Radiation Exposure
• Uranium Radiation Individual Dose Calculator
• Health Effects of Radiation: Dose and Risk

Introduction

Uranium is a metal of high density (18.9 g/cm³). The earth's crust contains an average of about 3 ppm (= 3 g/t) uranium, and seawater approximately 3 ppb (= 3 mg/t).
Naturally occuring uranium consists of three isotopes, all of which are radioactive: U-238, U-235, and U-234. U-238 and U-235 are the parent nuclides of two independent decay series, while U-234 is a decay product of the U-238 series.

 

 

Uranium Decay Series

see also:

• Uranium Decay Calculator
• Universal Decay Calculator (includes look up of nuclide data)
• Unit Converter: Specific activity <-> half-life · Decay <-> half-lives · Decay <-> time

 

Uranium-238 Decay Series (image) Nuclide Half-Life Radiation * U-238 4.468 · 109 years alpha Th-234 24.1 days beta Pa-234m 1.17 minutes beta U-234 244,500 years alpha Th-230 77,000 years alpha Ra-226 1,600 years alpha Rn-222 3.8235 days alpha Po-218 3.05 minutes alpha Pb-214 26.8 minutes beta Bi-214 19.9 minutes beta Po-214 63.7 microseconds alpha Pb-210 22.26 years beta Bi-210 5.013 days beta Po-210 138.378 days alpha Pb-206 stable - only major decays shown * in addition, all decays emit gamma radiation Average decay energies of U-238 series (click to enlarge in new window)

Uranium-235 Decay Series Nuclide Half-Life Radiation * U-235 703.8 · 106 years alpha Th-231 25.52 hours beta Pa-231 32,760 years alpha Ac-227 21.773 years beta Th-227 18.718 days alpha Ra-223 11.434 days alpha Rn-219 3.96 seconds alpha Po-215 778 microseconds alpha Pb-211 36.1 minutes beta Bi-211 2.13 minutes alpha Tl-207 4.77 minutes beta Pb-207 stable - only major decays shown * in addition, all decays emit gamma radiation Average decay energies of U-235 series (click to enlarge in new window) Ac: Actinium Bi: Bismuth Pa: Protactinium Pb: Lead Po: Polonium Ra: Radium Rn: Radon Th: Thorium Tl: Thallium U: Uranium

In natural uranium, these decay chains generally are in secular equilibrium. This means that in 1 g of natural uranium each nuclide of the U-238 series has an activity of 12,356 Bq and each nuclide of the U-235 series an activity of 568 Bq.
In the various processing steps of nuclear fuel production, the equilibrium is destroyed.

Uranium Ore

In an uranium ore deposit, secular equilibrium obtains between U-238 and its decay products, and between U-235 and its decay products. The equilibrium may be somewhat disturbed by geochemical migration processes in the ore deposit.
An ore grade of 1% U₃O₈ is equivalent to 0.848% U, and 1 million lbs U₃O₈ are equivalent to 385 metric tonnes of U. (see also Unit Converter: Uranium concentration (wt.) · Uranium weight)

Uranium Ore Activity (U-238 series) (click to enlarge in new window)

In case of an undisturbed uranium deposit, the activity of all decay products remains constant for hundreds of millions of years. (see also: Uranium Decay Calculator)

 

The radiation is virtually trapped underground; exposures are only possible if contaminated groundwater, that is circulating through the deposit, is used for drinking. Radon is of no concern for deep deposits, though it can travel through underground fissures, since it decays before it can reach the surface.

The situation changes completely, when the deposit is mined: Radon gas can escape into the air, ore dust can be blown by the wind, and contaminants can be leached and seep into surface water bodies and groundwater.

 

The alpha radiation of the 8 alpha emitting nuclides contained in the U-238 series (and to a lesser degree, of the 7 alpha emitters in the U-235 series) presents a radiation hazard on ingestion or inhalation of uranium ore (dust) and radon. The gamma radiation mainly of Pb-214 and Bi-214, together with the beta radiation of Th-234, Pa-234m, Pb-214, Bi-214, and Bi-210, presents an external radiation hazard. For ingestion and inhalation, also the chemical toxicity of uranium has to be taken into account.

Uranium In-situ Leach Solution

See also Impacts of Uranium In-Situ Leaching

The uranium concentration in the solution produced from in-situ leaching wells depends on a number of parameters, an important one being time from startup. The initial concentration from an individual well soon peaks in a few days at values of typically 300 - 600 mg/l and then declines rapidly. The decline slows down as the concentration reaches 30 - 50 mg/l. The well is usually shut in when the concentration reaches 10 - 20 mg/l after 8 - 18 months operation. Average uranium concentrations are typically 40 - 70 mg/l. [IAEA1989 p.17]
Various decay products of uranium are also leached and can reach considerable activities in the leaching solution, depending on the leaching agent used. During processing of the solution, large amounts of the radon contained escape into the atmosphere, while the other decay products are transferred to the waste solutions. Those solutions usually are dumped in deep aquifers through disposal wells, or evaporated in ponds, resulting in a concentrated waste slurry.

Radon

See also: Radon Individual Dose Calculator

Most of the radiation hazard results from the inhalation of the short-lived radon progeny (Po-218, Pb-214, Bi-214, and Po-214). Radon itself is of minor concern, since most of the inhaled radon is exhaled. And most of the longer-lived Pb-210 (22 year half-life) and its progeny are eliminated from the body before they decay.

Radon and Progeny Activity (click to enlarge in new window)

Long-lived Radon Progeny Activity (click to enlarge in new window)

There are a number of units in use to describe radon and radon progeny activity concentration in air: (see also Unit Converter: Activity conc. radon <-> radon progeny)

• Bq/m³ and pCi/l for the activity concentration of radon-222 in air:
  1 pCi/l (pico-Curie or 10^-12 Curie per liter) is equivalent to 37 Bq/m³ (Becquerel per cubic meter)
• J/m³, WL and Bq/m³ EEC for the activity concentration of radon-222 progeny in air:
  1 WL (Working Level) is equivalent to 101.3 pCi/l (3746 Bq/m³) of radon-222 in equilibrium with its short-lived decay products.
  1 J/m³ (Joule per cubic meter) is equivalent to 1.8 · 10⁸ Bq/m³ of radon-222 in equilibrium with its short-lived decay products.
  EEC (equilibrium equivalent concentration) is defined as the activity concentration of radon in radioactive equilibrium with its short-lived progeny that has the same potential alpha energy concentration as the actual non-equilibrium mixture.

The unit of WLM describes exposure to radon-222 progeny:
1 WLM (Working Level Month) is defined as the exposure to 1 WL during 170 hours.

The Equilibrium Factor describes the fraction of potential alpha decay energy of the short-lived radon decay products, compared to secular equilibrium. The equilibrium factor is defined as:
F = (0.106 c_Po-218 + 0.514 c_Pb-214 + 0.380 c_Bi-214) / c_Rn-222
where c_x stands for the activity concentration of the nuclide x.
Indoors, the equilibrium factor is depending on the ventilation rate; outdoors it is depending on distance from the source and wind speed.
Typical values are 0.4 for indoors or work, and 0.8 for outdoors.

Uranium Ore Concentrate (U₃O₈)

The uranium ore concentrate ("Yellow Cake") produced in the milling process contains a mixed oxide usually referred to as "U₃O₈" (UO₂ · 2 UO₃). Due to a number of impurities contained, it needs further refining before it can be used for nuclear fuel production. 1 t U₃O₈ is equivalent to 0.848 t U.

Natural Uranium Activity (U-238 series) (click to enlarge in new window)

Initially, it only contains the uranium isotopes. Within a few days, Th-231 (U-235 series), and within a few months, Th-234 and Pa-234m (U-238 series) grow in. The activity then remains stable for more than 10,000 years. After this time, Th-230 and all other decay products of the U-238 series, and Pa-231 and all other decay products of the U-235 series grow in. This could, however, only occur with residual ore concentrate not consumed for nuclear fuel production. (see also: Uranium Decay Calculator)

The alpha radiation of the uranium isotopes U-238, U-235, and U-234 presents a radiation hazard on ingestion or inhalation of natural uranium. The beta radiation of Th-234 and Pa-234m, together with the weak gamma radiation emitted by all nuclides, presents an external radiation hazard. For ingestion and inhalation, also the chemical toxicity of uranium has to be taken into account.

Uranium Mill Tailings

(see also: Introduction: Uranium Mill Tailings Deposits)

Uranium mill tailings are the residual waste from the process of uranium extraction from the uranium ore. Since only uranium is extracted, all other members of the uranium decay chains remain in the tailings at their original activities. In addition, small residual amounts of uranium are left in the tailings, depending on the efficiency of the extraction process used.

Uranium Mill Tailings Activity (U-238 series) (click to enlarge in new window)

Within a few months, the isotopes of Th-234 and Pa-234m decay to the value given by the residual activity of the U-238. The total activity in the tailings then remains constant for more than 10,000 years at about 85% of that in the ore. Only after several hundred thousand years, when the Th-230 has decayed to the level of the residual U-234, a major decrease of total activity takes place. After this time, the activity of all members of the U-238 chain is equal to that of the residual U-238 and U-234, and it remains at this level for some billion years. (see also: Uranium Decay Calculator)

Compared to uranium ore, the alpha radiation of uranium mill tailings and thus the radiation hazard on ingestion or inhalation of tailings (dust) is approx. 25% lower, while the hazard from radon is unchanged. The external radiation hazard from gamma radiation remains nearly unchanged, while that from beta radiation is reduced. The chemical toxicity of uranium plays a minor role only in tailings.

Heavy Water Reactor Fuel (natural UO₂)

For use in heavy water reactors (HWR, such as CANDU type, or pressurized heavy water reactors - PHWR), the uranium is needed in the form of UO₂. This is obtained from the uranium ore concentrate by refining and conversion. 1 t of UO₂ is equivalent to 0.8815 t U.

Magnox Reactor Fuel (natural U metal)

For use in Magnox reactors (graphite moderated, cas cooled), the uranium is needed in the form of uranium metal. This is obtained from the uranium ore concentrate by refining and conversion.

In addition to the radiological and chemical hazards, uranium metal presents a hazard from spontaneous ignition of finely divided particles (pyrophoricity).

Uranium Hexafluoride (UF₆)

For the use in light water reactors (LWR, such as boiling water reactors - BWR, or pressurized water reactors - PWR), the fissile isotope of uranium-235 contained in the natural uranium has to be enriched. For the enrichment process, uranium is needed in the form of uranium hexafluoride (UF₆). This is obtained from the uranium ore concentrate by refining and conversion. 1 t of UF₆ is equivalent to 0.676 t U.
At ambient temperature, UF₆ is a crystalline solid, but at a temperature of 56.4°C, it sublimates (becomes a gas). Chemically, UF₆ is very reactive: with water (atmospheric humidity!) it forms the extremely corrosive hydrofluoric acid and the highly toxic uranyl fluoride (UO₂F₂). The hydrofluoric acid causes skin burns, and, after inhalation, damages the lungs. Further health hazards result from the chemical toxicity of the uranium to the kidneys, and from the alpha radiation of the uranium.

Additional hazards exist, if the uranium hexafluoride contains uranium recovered from reprocessing of spent nuclear fuel. In this case, the uranium hexafluoride is contaminated with fission products (mainly ruthenium-106 and technetium-99 ), with artificial uranium isotopes (U-232 , U-233 , U-236 , and U-237 ), with transuranics (such as neptunium-237 and plutonium-239 ), and with the decay products of all these nuclides.

Uranium-232 Series Activity (click to enlarge in new window)

Uranium-232 is of special concern, since some of its decay products are strong gamma emitters (in particular thallium-208 ). While the activity of the fission products slowly decreases with time due to radioactive decay, the activity of the U-232 progeny (and thus its gamma radiation) strongly increases during the first 10 years, until secular equilibrium with U-232 is obtained. (see also: Uranium Decay Calculator)

 

Source: [Neghabian1991] p.83

The UF₆ is shipped in steel cylinders containing up to 12.7 tonnes. If cylinders are involved in long-lasting fires during accidents, large amounts of UF₆ can be released within a short time.

> see also Uranium Hexafluoride Hazards.

Enriched UF₆

For use in pressurized water reactors (PWR), uranium is enriched to between 3.6% and 4.1%, and for use in boiling water reactors (BWR), between 3.0% and 3.2% weight-percent uranium-235; that is around 4 to 6 times the natural concentration. As a side effect, the concentration of uranium-234 is enriched at an even higher ratio, according to its lower atomic weight.

If the UF₆ feed contained uranium recycled from spent fuel, then the lighter uranium nuclides U-232 and U-233 mainly and U-236 partly end up in the enriched UF₆ product. Any fission products present, such as technetium-99, completely end up in the enriched UF₆ product.

after [Neghabian1991] p.90

In addition to the hazards already described, handling of the enriched uranium presents a criticality hazard: if too large amounts of enriched uranium are accumulated in one place, uncontrolled chain reactions can occur, causing heavy releases of neutron and gamma radiation.

Depleted UF₆

The waste product from the enrichment process is depleted in uranium-235, it is therefore referred to as "depleted uranium". Typical concentrations of U-235 in depleted uranium (the "tails assay") are 0.2 to 0.3 weight-percent; that is around 30 - 40% of its concentration in natural uranium. The concentration of uranium-234 is depleted to an even lower ratio, according to its lower atomic weight.
The tails assay is a parameter that can be adjusted to economical needs, depending on the cost of fresh natural uranium and on the enrichment cost (expressed in $ per separative work unit - SWU).
> See graphs: Cost balance of uranium enrichment · Optimal tails assay
(Note: feed cost includes uranium price plus conversion cost)
For current prices, see Ux Industry Spot Prices

 

Depleted Uranium Activity (U-238 series) (click to enlarge in new window)

Within a few months, the isotopes of Th-234 and Pa-234m grow in to the value given by the activity of the U-238. The total activity in the depleted uranium then remains constant for around 10,000 years. Then, Th-230 with all its decay products starts growing in. After around 100,000 years, U-234 grows in to the activity level given by the U-238, further promoting the ingrowth of Th-230 and decay products. After around 2 million years, all nuclides are in secular equilibrium, and the total activity reaches a maximum and remains at this level for a billion years. From residual U-235, Th-231 grows in within a few days. After around 10,000 years, Pa-231 and all other decay products of the U-235 series start growing in. (see also: Uranium Decay Calculator)

Depleted uranium thus has the unusual property that it becomes more hazardous with time - an effect that has to be taken intoo aaccount for its long-term management as a waste.

If the UF₆ feed contained uranium recycled from spent fuel, then the heavier uranium nuclides U-236 and U-237 partly end up in the depleted UF₆ tails. Any transuranics present, such as neptunium-237 and plutonium-239, mainly end up in the tails.

after [Neghabian1991] p.90

Most of the depleted UF₆ produced so far is being stored in steel cylinders in so-called cylinder yards near the enrichment plants. In the storage yards, the cylinders are subject to corrosion. The integrity of the cylinders must therefore be monitored and the painting must be refreshed from time to time. This maintenance work requires moving of the cylinders, causing further hazards from breaching of corroded cylinders, and from handling errors. (see Cylinder Storage of Depleted UF₆)
As a worst-case scenario, the crash of an airplane into a cylinder yard must be assumed.

Light Water Reactor Fuel (enriched UO₂)

In a re-conversion process, the enriched uranium hexafluoride is converted to the oxide form of UO₂. In this form, the uranium is used for the production of nuclear fuel for light water reactors. 1 t of UO₂ is equivalent to 0.8815 t U.
If the UF₆ contained uranium recycled from spent fuel, then the nuclear fuel may be contamined with the artificial uranium isotopes of U-232, U-233, and U-236, and with fission products such as technetium-99.
Production and handling of this material, as of all enriched uranium, presents a criticality hazard: if too large amounts of enriched uranium are accumulated in one place, uncontrolled chain reactions can occur, causing heavy releases of neutron and gamma radiation.

Depleted Uranium Metal

In a re-conversion process, the depleted uranium hexafluoride can be converted to the form of uranium metal.

If the UF₆ contained uranium recycled from spent fuel, then the depleted uranium may be contaminated with the artificial uranium isotopes U-236 and U-237, and with transuranics such as neptunium-237 and plutonium-239.

In addition to the radiological and chemical hazards, (depleted) uranium metal presents a hazard from spontaneous ignition of finely divided particles (pyrophoricity).

Depleted Uranium Oxide (UO₂ or U₃O₈)

In a re-conversion process, the depleted uranium hexafluoride can be converted to the oxide form of UO₂ or U₃O₈. In these forms, the depleted uranium is chemically more stable and suitable for long-term storage or disposal (see Waste Management - Depleted Uranium).
1 t of UO₂ is equivalent to 0.8815 t U, and 1 t U₃O₈ is equivalent to 0.848 t U.

If the UF₆ contained uranium recycled from spent fuel, then the depleted uranium may be contaminated with the artificial uranium nuclides U-236 and U-237, and with transuranics such as neptunium-237 and plutonium-239.

References

 [IAEA1989] In Situ Leaching of Uranium: Technical, Environmental and Economic Aspects, IAEA-TECDOC-492, IAEA Vienna 1989, 172 p.

 

 

Impacts of Uranium In-Situ Leaching

(last updated 24 Feb 2000)

Contents:

• Existing and Proposed Sites
• Environmental Impacts
• Reclamation Concepts
• Reclamation Projects
• References
• Further Information

In the case of in-situ leaching (ISL), or solution mining, the uranium-bearing ore is not removed from its geological deposit, but a leaching liquid is injected through wells into the ore deposit, and the uranium bearing liquid is pumped from other wells. In-situ leaching gains importance for the exploitation of low grade ore deposits, for its low production cost. Many new projects for uranium in-situ leaching are being planned at present.

Existing and Proposed Uranium In-Situ Leaching Sites

The USA produced 1684 t U from in-situ leaching in 1996, this corresponds to 93% of all uranium produced in that year. The ISL operations are mainly located in Wyoming, Texas and Nebraska. For current U.S. ISL operations, see Operating Status of Nonconventional Uranium Plants and U.S. Uranium Mine Production (US DOE).
New ISL projects are being proposed for Texas, Wyoming, and New Mexico.

In Eastern Germany, an underground mine converted to an in-situ leaching facility was in operation at Königstein near Dresden until the end of 1990. It produced a total of 18,000 t U, 30% of which were from ISL with sulfuric acid.

In the Czech Republic, in-situ leaching with sulfuric acid was used on a large scale at Stráz pod Ralskem in North Bohemia: The ore deposit is located in Cretaceous sandstones with grades of 0.08 - 0.15% uranium. In an area of 5.6 km², 9340 wells were drilled from the surface into the deposit. The total production to 1994 was 13,835 t U.

In Bulgaria, in-situ leaching was in use at many locations. The first uranium mines in Bulgaria were underground mines. From 1979, in-situ leaching was also applied, using wells, drilled from the surface. The leaching agent used in most cases was sulfuric acid. From 1981, in-situ leaching was also used to increase the yield from mined out conventional underground mines [Tabakov1993]. From 1981, 23 ore deposits were mined by conventional underground mining techniques, 17 by in- situ leaching from the surface, and 11 by in-situ leaching in combination with conventional mining techniques. In 1990, 70% of the uranium produced was from in-situ leaching of ore deposits with very low grades of 0.02 - 0.07% of uranium [Kuzmanov1993]. In the years 1991 - 1992, 14,000 wells in 15 in-situ leaching fields were in operation [OECD1994]. The total area used for in- situ leaching comprised 6 km² [Vapirev1996]. The total production from in-situ leaching to 1994 was 5,175 t U [OECD1996].

In Ukraine, ISL has been used at the Devladove, Bratske, and Safonovskoye sites from 1966 - 1983.

In Russia, a new ISL project is being proposed for Dalmatovkoye in Western Siberia.

In Kazakhstan, in-situ leaching is being used at the Kandjugan, Uvanas, Mynkuduk, Karamurun sites. In 1994, the production from ISL was 1580 t U, a 70% share in the country's uranium production; the total production from ISL to 1994 was 19,961 t U [OECD1996]. The new projects of Muyunkum and Inkay are also planned for exploitation by ISL.

In Uzbekistan, in-situ leaching (with sulfuric acid) is being used at the Uchkuduk, Zarafabad, and Nurabad deposits, covering a total area of 13 km². Since 1995, all production is from ISL (3050 t U annually) [OECD1996].

In China, ISL is being used at Tengchong and Yining.

In Australia, new ISL projects are being proposed for Beverley and Honeymoon in South Australia.

Environmental Impacts

The leaching liquid used for in-situ leaching contains the leaching agent ammonium carbonate for example, or - particularly in Europe - sulfuric acid. This method can only be applied if the uranium deposit is located in porous rock, confined in impermeable rock layers.

> View images: ISL general arrangement (19k) · ISL detail (7k) (WMA/Cogema)

The advantages of this technology are:

• the reduced hazards for the employees from accidents, dust, and radiation,
• the low cost;
• no need for large uranium mill tailings deposits.

The disadvantages of the in-situ leaching technology are:

• the risk of spreading of leaching liquid outside of the uranium deposit, involving subsequent groundwater contamination,
• the unpredictable impact of the leaching liquid on the rock of the deposit,
• the impossibility of restoring natural groundwater conditions after completion of the leaching operations.

Moreover, in-situ leaching releases considerable amounts of radon, and produces certain amounts of waste slurries and waste water during recovery of the uranium from the liquid.

Scheme of normal ISL operation

> View Typical failure modes during ISL operation (animation - 58k)

In the case of Königstein (Germany), a total of 100,000 tonnes of sulfuric acid was injected with the leaching liquid into the ore deposit. At present, 1.9 million m³ of leaching liquid are still locked in the pores of the rock leached so far; a further 0.85 million m³ are circulating between the leaching zone and the recovery plant. The liquid contains high contaminant concentrations, for example, expressed as multiples of the drinking water standards: cadmium 400x, arsenic 280x, nickel 130x, uranium 83x, etc. This liquid presents a hazard to an aquifer that is of importance for the drinking water supply of the region.

Groundwater impact is much larger at the Czech in-situ leaching site of Stráz pod Ralskem: 28.7 million m³ of contaminated liquid is contained in the leaching zone, covering an area of 5.74 km². This zone contains a total of 1.5 million tonnes of sulphate, 37,500 tonnes of ammonium, and others. In addition to the chemicals needed for the leaching operation (including 3.7 million tonnes of sulfuric acid, among others), 100,000 tonnes of ammonium were injected; they were a waste product resulting from the recovery of uranium from the leaching liquid.
Moreover, the contaminated liquid has spread out beyond the leaching zone horizontally and vertically, thus contaminating another area of 28 km² and a further 235 million m³ of groundwater. To the southwest, the groundwater contamination has already reached the second zone of groundwater protection of the potable water supply of the town of Mimon. In southeastern direction, the contaminated groundwater is still at a distance of 1.2 - 1.5 km from the second zone of groundwater protection of the Dolánky potable water wells, which supply 200 l/s for the city of Liberec [Andel1996]. The migration of the contaminated liquids in an easterly direction towards the Hamr I underground mine is at present intercepted by a hydraulic barrier: decontaminated water is injected into a chain of wells to prevent further migration of the contaminated groundwater.

In Bulgaria, a total of 2.5 million tonnes of sulfuric acid was injected into the ore deposits exploited by in-situ leaching. It is estimated that about 10% of the surface area used for ISL could be contaminated from solution spills. This is of concern, since the area is to be returned to its previous owners for agricultural use.
After termination of the ISL operations, the contaminated groundwater spreads offsite. Some in-situ leaching facilities (for example Bolyarovo, Tenevo/Okop) are located close to drinking water wells. [Vapirev1996]
The impacts of ISL on surface and groundwater are catastrophic:

"Very high concentrations of sulfate ions are measured in surface water and even in wells of private owners as a result of accidental spilling of solutions in sites of in-situ leaching. At the site "Cheshmata" (Haskovo), in the valley downstream from the sorption station, the measured content of sulfates is 1400 mg/l, free H2SO4 is 392 mg/l and pH is 2.2 (5.5 - 8.5 for 3-rd category water). A similar case has been recorded in Navusen where in a valley the sulfate concentration is 13362 mg/l and almost 5 g/l H2SO4, which means that actually the water is leaching solution.
In the underground water of such sites the salt content is >20 g/l, from which the sulfates are 12-15 g/l." [Dimitrov1996]

The Devladovo site in Ukraine was leached with sulfuric and nitric acid. The surface of the site was heavily contaminated from spills of leaching solutions. Groundwater contamination is spreading downstream from the site at a speed of 53 m/year. It has traveled a distance of 1.7 km already and will reach the village of Devladovo after 24.5 years. [Molchanov1995]

Typical examples for the incidents occuring during business as usual at in-situ operations, including surface spills and underground solution excursions, can be found here: Christensen Ranch (Wyoming), Highland (Wyoming), Smith Ranch (Wyoming), Kingsville Dome (Texas), Rosita (Texas), Bruni (Texas)

Reclamation Concepts After In-Situ Leaching

After termination of an in-situ leaching operation, the waste slurries produced must be safely disposed, and the aquifer, contaminated from the leaching activities, must be restored. Groundwater restoration is a very tedious process that is not yet fully understood. So far, it is not possible to restore groundwater quality to previous conditions.

The best results have been obtained with the following treatment scheme, consisting of a series of different steps [Schmidt1989], [Catchpole1995]:

• Phase 1: Pumping of contaminated water: the injection of the leaching solution is stopped and the contaminated liquid is pumped from the leaching zone. Subsequently, clean groundwater flows in from outside of the leaching zone.
• Phase 2: as 1, but with treatment of the pumped liquid (by reverse osmosis) and re-injection into the former leaching zone. This scheme results in circulation of the liquid.
• Phase 3: as 2, with the addition of a reducing chemical (for example hydrogen sulfide H₂S or sodium sulfide Na₂S). This causes the chemical precipitation and thus immobilization of major contaminants.
• Phase 4: Circulation of the liquid by pumping and re- injection, to obtain uniform conditions in the whole former leaching zone.

But, even with this treatment scheme, various problems remain unresolved:

• Contaminants, that are mobile under chemically reducing conditions, such as radium, cannot be controlled,
• if the chemically reducing conditions are later disturbed for any reasons, the precipitated contaminants are re-mobilized,
• the restoration process takes very long periods of time,
• not all parameters can be lowered appropriately.

Most restoration experiments reported refer to the alkaline leaching scheme, since this scheme is the only one used in Western world commercial in-situ operations. Therefore, nearly no experience exists with groundwater restoration after acid in- situ leaching, the scheme that was applied in most instances in Eastern Europe. The only Western in-situ leaching site restored after sulfuric acid leaching so far, is the small pilot scale facility Nine Mile Lake near Casper, Wyoming (USA). The results can therefore not simply be transferred to production scale facilities. The restoration scheme applied included the first two steps mentioned above. It turned out that a water volume of more than 20 times the porevolume of the leaching zone had to be pumped, and still several parameters did not reach background levels. Moreover, the restoration required about the same time as used for the leaching period [Nigbor1982] [Engelmann1982].

Reclamation Projects

In USA, the Pawnee, Lamprecht, and Zamzow ISL Sites in Texas were restored using steps 1 and 2 of the above listed treatment scheme [Mays1993]. Relaxed groundwater restoration standards have been granted at these and other sites, since the restoration criteria could not be met (see details).

For the Königstein (Germany) in-situ leaching mine, there are still no large-scale proven methods to remove the remaining leaching liquid from the deposit and to inhibit continued leaching of uranium and other contaminants. The impact is rather severe, as the mining activities damaged an aquifer used for the drinking water supply in the Dresden area.
At present, it is planned to flood the Königstein mine (which is an underground mine converted to in-situ leaching in some areas), up to a certain groundwater level, to wash the leaching blocs. The flooding should be halted and the flooding waters be contained and treated, until their contaminant concentrations would only be marginal. It must be anticipated, though, that this procedure might take long periods of time, as the leaching zone is no longer washed under pressure, unlike during the leaching action.

The situation is even more difficult in the Czech in-situ leaching facility of Stráz pod Ralskem: the goal of restoring groundwater quality in the leaching zone to background has been abandoned as unrealistic.
The restoration goal for the upper aquifer above the leaching zone (used for potable water supply), however, is the drinking water standard, to be achieved by pumping of contaminated waters. The goal seems to be attainable for this aquifer, although some contaminants, as aluminium, exceed the standard up to 1000-fold.
But, for the leaching zone and its surroundings, the goal of reaching the potable water standard is regarded as absolutely unrealistic. For this aquifer, the goal is defined that anticipated contaminant migration to the upper aquifer shall not worsen the water quality in this aquifer beyond potable water standards. But it is still unclear, which contaminant level in the lower aquifer is sufficient to achieve this goal. According to modeling results, a level of total dissolved solids of 10 g/l will be reached in the year 2014, and a level of 1 g/l in 2032, after continuous pumping.
> View details on Stráz groundwater restoration project.

In Bulgaria, a restoration attempt using recirculation of the solution without addition of acid failed: the tubes and filters of the sorption columns plugged, and all restoration attempts were stopped [Vapirev1996]. In some cases, heavy metals and rare earth elements (V, W, Mo, La) were detected in groundwater due to the recycling of solution [Dimitrov1996]. At present, the installations at the surface of the ISL sites are being decommissioned, and all pipes are being removed. But, there is no groundwater restoration: the ISL wells are being plugged; and the groundwater is submitted to "natural restoration".

The restoration of the Devladovo ISL site in Ukraine was limited to soil cleanup at the surface. Some heavily contaminated soil was replaced, while deep ploughing was the only remedy used at the major part of the site. Cleanup was finished in 1975. Subsequently, the site has been used for agriculture. Surveys performed in 1991 have shown that the radionuclide concentrations in the soil had not decreased at all, and that the anticipated self-cleaning of the soil had not taken place. Effective dose equivalents of up to 0.2 mSv/year were calculated for the members of the local population consuming the wheat grown on this soil. [Molchanov1995]

References

• [Andel1996] Andel,P; Pribán,V: Environmental restoration of uranium mines and mills in the Czech Republic. In: Planning for environmental restoration of radioactively contaminated sites in central and eastern Europe, Vol.1: Identification and characterization of contaminated sites, IAEA- TECDOC-865, Vienna 1996, p.113-135
• [Catchpole1995] Catchpole,Glenn; Kirchner,Gerhard: Restoration of Groundwater Contaminated by Alkaline In-Situ Leach of Uranium Mining. In: Merkel,B et al. (Ed.): Uranium Mining and Hydrogeology, GeoCongress 1, Köln 1995, p.81-89
• [Dimitrov1996] Dimitrov,M; Vapirev,E I: Uranium Industry in Bulgaria and Environment: Problems and Specific Features of the Period of the Technical Close-Out and Remediation of the Negative Consequences. In: Planning for environmental restoration of radioactively contaminated sites in central and eastern Europe, Vol.2: Planning for environmental restoration of contaminated sites, IAEA-TECDOC-865, Vienna 1996,p.43-52
• [Engelmann1982] Engelmann,W H; Phillips,P E; Tweeton,D R; Loest,K W;Nigbor,M T: Restoration of Groundwater Quality Following Pilot-Scale Acidic In-Situ Uranium Leaching at Nine- Mile Lake Site Near Casper, Wyoming. In: Society of Petroleum Engineers Journal, June 1982, p.382-398
• [Kuzmanov1993] Kuzmanov,L; Simov,S D; Valkov,T; Vasilev,D: In-Situ Leaching of Uranium in Bulgaria: Geological, Technological and Ecological Considerations. In: IAEA (Ed.), Uranium in situ leaching. Proceedings of a Technical Committee Meeting held in Vienna, 5-8 October 1992, IAEA-TECDOC-720, Vienna 1993, p.65-73
• [Mays1993] Mays,W M: Restoration of Groundwater at Three In- Situ Uranium Mines in Texas. In: IAEA (Ed.), Uranium in situ leaching. Proceedings of a Technical Committee Meeting held in Vienna, 5-8 October 1992, IAEA-TECDOC-720, Vienna 1993, p.191- 215
• [Molchanov1995] Molchanov,A; Soroka,Y; Isayeva,N; Mordberg,E: The State of Environment on Former Site of In-Situ Leaching of Uranium. In: Slate,S; Baker,R; Benda,G (Eds.), Proceedings of the Fifth International Conference on Radioactive Waste Management and Environmenttal Remediation, ICEM'95, Vol.2 - Management of Low-Level Waste and Remediation of Contaminated Sites and Facilities, ASME, New York, 1995, p.1507-1510
• [Nigbor1982] Nigbor,Michael T; Engelmann,William H; Tweeton,Daryl R: Case History of a Pilot-Scale Acidic In Situ Uranium Leaching Experiment. United States Department of the Interior, Bureau of Mines Report of Investigations RI-8652, Washington D.C., 1982, 81 p.
• [OECD1994] Uranium 1993 Resources, Production and Demand, OECD Nuclear Energy Agency/International Atomic Energy Agency (Ed.), Paris 1994, 311 p.
• [OECD1996] Uranium 1995 Resources, Production and Demand, OECD Nuclear Energy Agency/International Atomic Energy Agency (Ed.), Paris 1996, 362 p.
• [Schmidt1989] Schmidt,C: Groundwater Restoration and Stabilization at the Ruth-ISL Test Site in Wyoming, USA. In: In Situ Leaching of Uranium - Technical, Environmental and Economic Aspects, Proceedings of a Technical Committee Meeting, IAEA- TECDOC-492, Vienna 1989, p.97-126.
• [Tabakov1993] Tabakov,B: Complete Mining of Uranium Deposits in Bulgaria by In-Situ Leaching Mining Systems Used After Conventional Mining. In: IAEA (Ed.), Uranium in situ leaching. Proceedings of a Technical Committee Meeting held in Vienna, 5-8 October 1992, IAEA-TECDOC-720, Vienna 1993, p.105-114
• [Vapirev1996] Vapirev,E I; Dimitrov,M; Minev,L; Boshkova,T; Pressyanov,D S; Guelev,M G: Radioactively contaminated sites in Bulgaria. In: Planning for environmental restoration of radioactively contaminated sites in central and eastern Europe, Vol.1: Identification and characterization of contaminated sites, IAEA-TECDOC-865, Vienna 1996, p.43-63

Table 7. Operating Status of Nonconventional Uranium Plants, 1999
Plant Owner(s)	Plant Name and State	Plant Type	Rated Capacitya (thousand pounds U3O8 per year)	Operating Status at the End of the Yearb
COGEMA Mining	West Cole (TX)	In Situ Leach	200	I (R)
Everest Exploration	Hobson (TX)	In Situ Leach	1,000	I (CI)
IMC-Agrico	Sunshine Bridge (LA)	Phosphate Byproduct	420	I (CP)
IMC-Agrico	Uncle Sam (LA)	Phosphate Byproduct	750	I (CP)
IMC-Agrico	Plant City (FL)	Phosphate Byproduct	608	I (CP)
IMC-Agrico	New Wales (FL)	Phosphate Byproduct	750	I (CP)
Malapai Resources	Christensen Ranch (WY)	In Situ Leach	650	O
Malapai Resources	Holiday-El Mesquite (TX)	In Situ Leach	600	I(R)
Malapai Resources	Irigaray (WY)	In Situ Leach	350	I (R)
Malapai Resources	O'Hern (TX)	In Situ Leach	NA	I (R)
Power Resources/Geomex (Converse County Mining Venture)	Highland (WY)	In Situ Leach	2,000	O
Quivira Mining (Rio Algom)	Smith Ranch (WY)	In Situ Leach	2,000	O
Uranium Resources	Kingsville Dome (TX)	In Situ Leach	1,300	I (CI)
Uranium Resources	Rosita (TX)	In Situ Leach	1,000	I (CP)
UUS/Geomex/KEPRA (Crow Butte Resources)	Crow Butte (NE)	In Situ Leach	1,000	O

 

^aMilling capacity based on data reported on Form EIA-858 for 1999.

^bI=Inactive at the end of the year. R=Reclamation (restoration in process or completed). CI=Closed indefinitely (following year restart not planned). CP=Closed permanently (will not be restarted). NA = Not Available. O=Operating at the end of the year.

Source: Energy Information Administration, Form EIA-858, "Uranium Industry Annual Survey" (1999).

 

 

Uranium Mining and Milling Wastes:
An Introduction

by Peter Diehl

(last updated 14 Nov 2000)

Contents:

• URANIUM MINES
• WASTE ROCK
• HEAP LEACHING
• IN SITU LEACHING
• MILLING OF THE ORE
• URANIUM MILL TAILINGS DEPOSITS
• Characteristics of uranium mill tailings
• Potential hazards from uranium mill tailings
• Concepts for tailings disposal
• Standards for uranium mill tailings management
• Reclamation of uranium mill tailings deposits
• DISPOSAL OF OTHER MATERIALS

URANIUM MINES

Most uranium ore is mined in open pit or underground mines. The uranium content of the ore is often between only 0.1% and 0.2%. Therefore, large amounts of ore have to be mined to get at the uranium. In the early years up until the 1960's uranium was predominantly mined in open pit mines from ore deposits located near the surface.

(image (50k): Ranger open pit mine, Australia)

(image (32k): Lodève open pit mine, France)

(image (57k) : Midnite Mine, WA, USA - AESE)

(image (36k) : Sweetwater open pit mine, Wyoming, USA - WMA)

Later, mining was continued in underground mines.
After the decrease of uranium prices since the 1980's on the world market, underground mines became too expensive for most deposits; therefore, many mines were shut down.
New uranium deposits discovered in Canada have uranium grades of several percent.
To keep groundwater out of the mine during operation, large amounts of contaminated water are pumped out and released to rivers and lakes. When the pumps are shut down after closure of the mine, there is a risk of groundwater contamination from the rising water level.
(see also Uranium Ore Radiation Properties)

 

WASTE ROCK

Waste rock is produced during open pit mining when overburden is removed, and during underground mining when driving tunnels through non-ore zones. Piles of so-called waste rock often contain elevated concentrations of radioisotopes compared to normal rock. Other waste piles consist of ore with too low a grade for processing. The transition between waste rock and ore depends on technical and economic feasibility.

All these piles threaten people and the environment after shut down of the mine due to their release of radon gas and seepage water containing radioactive and toxic materials.

(image (36k): The waste rock "pyramids" of Ronneburg, Germany)

Waste rock was often processed into gravel or cement and used for road and railroad construction. VEB Hartsteinwerke Oelsnitz in Saxony has processed 200,000 tonnes of material per year into gravel containing 50 g/t uranium. Thus, gravel containing elevated levels of radioactivity were dispersed over large areas.

 

HEAP LEACHING

In some cases uranium has been removed from low-grade ore by heap leaching. This may be done if the uranium contents is too low for the ore to be economically processed in a uranium mill. The leaching liquid (often sulfuric acid) is introduced on the top of the pile and percolates down until it reaches a liner below the pile, where it is caught and pumped to a processing plant.
During leaching, piles present a hazard because of release of dust, radon gas and leaching liquid.
After completion of the leaching process, a longterm problem may result from naturally induced leaching if the ore contains the mineral pyrite (FeS₂), as with the uranium deposits in Thuringia, Germany) or Ontario, Canada. Then, acces of water and air may cause continuous bacterially induced production of sulfuric acid inside the pile, which results in the leaching of uranium and other contaminants for centuries and possibly permanent contamination of ground water.

 

IN SITU LEACHING

With the in situ leaching technology, a leaching liquid (e.g. ammonium-carbonate or sulfuric acid) is pumped through drill- holes into underground uranium deposits, and the uranium bearing liquid is pumped out from below. This technology can only be used for uranium deposits located in an aquifer in permeable rock, confined in non-permeable rock.

> View also images: ISL general arrangement (19k) · ISL detail (7k) (WMA/Cogema)

In situ leaching gains importance with a decrease in price of uranium. In the USA, in situ leaching is often used. In 1990, in Texas alone in situ leaching facilities for uranium were operated at 32 sites. In Saxony, Germany, an underground mine converted to an underground in situ leaching mine was operated until end of 1990 at Königstein near Dresden. In the Czech Republic, the in situ leaching technology was used at a large scale at Stráz pod Ralskem in Northern Bohemia.
The advantages of this technology are:

• The reduced risk for the employees from accidents and radiation;
• the lower cost; and
• no need for large tailings piles.

The disadvantages are:

• The risk of leaching liquid excursions beyond the uranium deposit and subsequent contamination of ground water;
• the unpredictable effects of the leaching liquid on the host rock of the deposit;
• the production of some amounts of waste sludge and waste water when recovering the leaching liquid; and
• the impossibility of restoring natural conditions in the leaching zone after finishing the leaching operation.

After finishing the in situ leaching, the waste sludge must be dumped in a final deposit and the ore zone aquifer must be restored to pre-leaching conditions. Ground water restoration is a very protracted and troublesome process, which is not yet completely understood. It is still impossible to establish pre- leach levels for all parameters.

(for details, see Impacts of Uranium In-Situ Leaching)

  MILLING OF THE ORE

Ore mined in open pit or underground mines is crushed and leached in a uranium mill. A uranium mill is a chemical plant designed to extract uranium from ore. It is usually located near the mines to limit transportation. In the most cases, sulfuric acid is used as the leaching agent, but alkaline leaching is also used. As the leaching agent not only extracts uranium from the ore, but also several other constituents like molybdenum, vanadium, selenium, iron, lead and arsenic, the uranium must be separated out of the leaching solution. The final product produced from the mill, commonly referred to as "yellow cake" (U₃O₈ with impurities), is packed and shipped in casks.
When closing down a uranium mill, large amounts of radioactively contaminated scrap are produced, which have to be disposed in a safe manner. In the case of Wismut's Crossen uranium mill, to reduce cost some of the scrap is intended to be disposed in the Helmsdorf tailings, but there it can produce gases and thus threaten the safe final disposal of the sludge.

 

URANIUM MILL TAILINGS DEPOSITS

Characteristics of uranium mill tailings

Uranium mill tailings are normally dumped as a sludge in special ponds or piles, where they are abandoned.. The largest such piles in the US and Canada contain up to 30 million tonnes of solid material. In Saxony, Germany the Helmsdorf pile near Zwickau contains 50 million tonnes, and in Thuringia the Culmitzsch pile near Seelingstädt 86 million tonnes of solids.

(image (79k) : Atlas Co. uranium mill tailings, Moab, Utah, USA)

(image (220k) : "A uranium mill tailings pond at the Panna Maria site in Karnes County, Texas" - U.S. DOE)

(image (37k) : Sweetwater tailings pond, Wyoming, USA - WMA)

(image (127k) : "Denison Tailings Basin, Elliot Lake, Ontario" - CDA)

(image (192k) : Uranium Tailings at Elliot Lake, Ontario - CCNR)

(image (39k): Ranger uranium mill tailings pond, Australia)

(image (24k): Helmsdorf uranium mill tailings dam, Oberrothenbach, Germany)

(image (15k) · image (60k) : Mecsekurán uranium mill tailings ponds, Pécs, Hungary)

The amount of sludge produced is nearly the same as that of the ore milled. At a grade of 0.1% uranium, 99.9% of the material is left over.
Apart from the portion of the uranium removed, the sludge contains all the constituents of the ore. As long lived decay products such as thorium-230 and radium-226 are not removed, the sludge contains 85% of the initial radioactivity of the ore. Due to technical limitations, all of the uranium present in the ore can not be extracted. Therefore, the sludge also contains 5% to 10% of the uranium initially present in the ore.
In addition, the sludge contains heavy metals and other contaminants such as arsenic, as well as chemical reagents used during the milling process.

Mining and milling removes hazardous constituents in the ore from their relatively safe underground location and converts them to a fine sand, then sludge, whereby the hazardous materials become more susceptible to dispersion in the environment. Moreover, the constituents inside the tailings pile are in a geochemical disequilibrium that results in various reactions causing additional hazards to the environment. For example, in dry areas, salts containing contaminants can migrate to the surface of the pile, where they are subject to erosion. If the ore contains the mineral pyrite (FeS₂), then sulfuric acid forms inside the deposit when accessed by precipitation and oxygen. This acid causes a continuous automatic leaching of contaminants.

Radon-222 gas emanates from tailings piles and has a half life of 3.8 days. This may seem short, but due to the continuous production of radon from the decay of radium-226, which has a half life of 1600 years, radon presents a longterm hazard. Further, because the parent product of radium-226, thorium-230 (with a half life of 80,000 years) is also present, there is continuous production of radium-226. (view Uranium decay series)

After about 1 million years, the radioactivity of the tailings and thus its radon emanation will have decreased so that it is only limited by the residual uranium contents, which continuously produces new thorium-230.

If, for example, 90% of the uranium contained in an ore with 0.1% grade was extracted during the milling process, the radiation of the tailings stabilizes after 1 million years at a level 33 times that of uncontaminated material. Due to the 4.5 billion year half-life of uranium-238, there is only a minuscule further decrease.
(see also Uranium Mill Tailings Radiation Properties)

Potential hazards from uranium mill tailings

Radionuclides contained in uranium tailings emit 20 to 100 times as much gamma-radiation as natural background levels on deposit surfaces. Gamma radiation levels decrease rapidly with distance from the pile.

The radium-226 in tailings continuously decays to the radioactive gas radon-222, the decay products of which can cause lung cancer. Some of this radon escapes from the interior of the pile. Radon releases are a major hazard that continues after uranium mines are shut down. The U.S. Environmental Protection Agency (EPA) estimates the lifetime excess lung cancer risk of residents living nearby a bare tailings pile of 80 hectares at two cases per hundred.
Since radon spreads quickly with the wind, many people receive small additional radiation doses. Although the excess risk for the individual is small, it cannot be neglected due to the large number of people concerned. EPA estimates that the uranium tailings deposits existing in the United States in 1983 would cause 500 lung cancer deaths per century, if no countermeasures are taken.
See also:

• Uranium Mill Tailings Radiation Properties
• Radiation Exposure of Residents at Uranium Mill Tailings
• Nuclear Fuel Population Health Risk Calculator

Tailings deposits are subject to many kinds of erosion. Due to the long half-lives of the radioactive constituents involved, safety of the deposit has to be guaranteed for very long periods of time.
After rainfall, erosion gullies can form; floods can destroy the whole deposit; plants and burrowing animals can penetrate into the deposit and thus disperse the material, enhance the radon emanation and make the deposit more susceptible to climatic erosion.
When the surface of the pile dries out, the fine sands are blown by the wind over adjacent areas. The sky has darkened from storms blowing up radioactive dust over villages located in the immediate vicinity of Wismut's uranium mill tailings piles. Subsequently, elevated levels of radium-226 and arsenic were found in dust samples from these villages.

Seepage from tailings piles is another major hazard. Seepage poses a risk of contamination to ground and surface water. Residents are also threatened by radium-226 and other hazardous substances like arsenic in their drinking water supplies and in fish from the area. The seepage problem is very important with acidic tailings, as the radionuclides involved are more mobile under acidic conditions. In tailings containing pyrite, acidic conditions automatically develop due to the inherent production of sulfuric acid, which increases migration of contaminants to the environment.

> View animation of modeled contaminant plume dispersion in groundwater (70k)
(Split Rock uranium mill tailings site, Wyoming)

Tailings dams are often not of stable construction. In most cases, they were made from sedimentation of the coarse fraction of the tailings sluge. Some, including those of Culmitzsch and Trünzig in Thuringia, were built on geologic faults. Therefore, they are subject to the risk of an earthquake. As the Thuringian tailings deposits are located in the center of an area of earthquake risk in the former GDR, they suffer a risk of dam failure. Moreover, strong rain or snow storms can also cause dam failures. (for details see: Safety of Tailings Dams)

It is of no surprise that again and again dam failures have occured. Some examples are:

• 1977, Grants, New Mexico, USA: spill of 50,000 tonnes of sludge and several million liters of contaminated water.
• 1979, Church Rock, New Mexico, USA: spill of more than 1000 t of sludge and about 400 million liters of contaminated water.
• 1984, Key Lake, Saskatchewan, Canada: spill of more than 100 million liters of contaminated liquids.

(see also Chronology of uranium tailings dam failures)

Occasionally, because of their fine sandy texture, dried tailings have been used for construction of homes or for landfills. In homes built on or from such material, high levels of gamma radiation and radon were found. The U.S. Environmental Protection Agency (EPA) estimates the lifetime excess lung cancer risk of residents of such homes at 4 cases per 100.

Concepts for tailings disposal

The obvious idea of bringing the tailings back to where the ore has been taken from, does not in the most cases lead to an acceptable solution for tailings disposal. Although most of the uranium was extracted from the material, it has not become less hazardous, quite to the contrary. Most of the contaminants (85% of the total radioactivity and all the chemical contaminants) are still present, and the material has been brought by mechanical and chemical processes to a condition where the contaminants are much more mobile and thus susceptible to migration into the environment. Therefore, dumping the tailings in an underground mine cannot be afforded in most cases; there, they would be in direct contact with groundwater after halting the pumps.

The situation is similar for deposit of tailings in former open pit mines. Here also, immediate contact to ground water exists, or seepage presents risks of contamination of ground water. Only in the case of the presence of proven impermeable geologic or man-made layers can the contamination risk to ground water be prevented. An advantage of in-pit deposition is relatively good protection from erosion.

(image (35k): Tailings disposal in Bellezane open pit, France)

In France and Canada, on the other hand, the concept of dumping the tailings in former open pits in groundwater is pursued or proposed at several sites in recent years.
In this case, a highly permeable layer is installed around the tailings, to allow free groundwater circulation around the tailings. Since the permeability of the tailings themselves is lower, it is anticipated (by the proponents) that nearly no exchange of contaminants between tailings and groundwater takes place. A similar method is being tested in Canada for the disposal of uranium mill tailings in lakes (called "pervious surround disposal").
Recent proposals even deny the necessity of an artificial permeable layer around the tailings, since the surrounding rock would provide a high enough permeability.

In most cases, tailings have to be dumped on the surface for lack of other options. Here, the protection requirements can more easily be controlled by appropriate methods, but additional measures have to be performed to assure protection from erosion.

Standards for uranium mill tailings management

In the early years of uranium mining after World War II, the mining companies often left sites without any clean up after the ore deposits were exhausted: often, in the United States, the mining and milling facilities were not even demolished, not to mention reclamation of the wastes produced; in Canada, uranium mill tailings were often simply dumped in one of the numerous lakes.

The untenability of this situation was for the first time recognized by U.S. legislation, which defined legal requirements for the reclamation of uranium mill tailings in 1978 (UMTRCA). On the basis of this law, regulations were promulgated by the Environmental Protection Agency (EPA: 40 CFR 192) and the Nuclear Regulatory Commission (NRC: 10 CFR 40). These regulations not only define maximum contaminant concentrations for soils and admissible contaminant releases (in particular for radon), but also the period of time, in which the reclamation measures taken must be effective: 200 - 1000 years. The reclamation action thhuus not only has to assure that the standards are met after completion of the reclamation work; but for the first time, a long-term perspective is included in such regulations. A further demand is that the measures taken must assure a safe disposal for the prescribed period of time without active maintenance. If these conditions cannot be met at the present site, the tailings must be relocated to a more suitable place.
Considering the actual period of time the hazards from uranium mining and milling wastes persist, these regulations are of course only a compromise, but they are a first step, at least. Regulations for the protection of groundwater were not included in the initial legislation; they were only promulgated in January 1995.

Last but not least, public involvement is given an important role in planning and control of the reclamation action.

Based on these regulations, various technologies for the safe and maintenance-free confinement of the contaminants were developed in the United States during subsequent years. The reclamation efforts also include the decontamination of homes in the vicinity built from contaminated material or on contaminated landfills.

In Canada, on the contrary, authorities decide on a site-by-site basis on the measures to be taken for reclamation; there are no legal requirements. The Atomic Energy Control Board (AECB) has only promulgated rough guidelines; and it decides, together with the mine and mill operators, on the necessity of measures to be taken. Therefore, it is no surprise that the Canadian approach results in a much lower level of protection. The proposals for the management of the uranium mill tailings in the Elliot Lake area, Ontario, for example, include no other "protective barrier" than a water cover.

Reclamation of uranium mill tailings deposits

To reclaim an uranium mill tailings pile according to principles of a safe long-term isolation, detailed investigations have to be performed in advance to assess the site.
If the tailings pile presents an immediate hazard, then intermediate protective measures can be taken in parallel, such as installation of a cover against windblown dust, or collection of seepage waters. These measures, however, should not conflict with long-term measures to be taken later.

The site must be appropriate for tailings disposal from the view of geology and hydrology:

• it should not be located on a geologic fault,
• it should not be threatened by the risk of earthquakes,
• natural impermeable layers should be present,
• the site should not be located in the flood plain of rivers,
• the phreatic level should be rather deep,
• any seepage should not present a risk to ground water,
• deposits of clay materials appropriate for lining and covering the deposit should not be located too far away,
• the site should be remote from residential areas, and so on.

During investigation of the site, ground water flow has to be monitored, to allow development of computer based three- dimensional ground water models. These models can be used for prediction of effects of supposed or real contaminant releases.

In some circumstances, it may become necessary, to move all of the material to an intermediate storage place to allow for the installation of a liner below the final deposit. An example for this procedure was the tailings deposit at Canonsburg, Pennsylvania, USA.
In some very unfortunate circumstances, it even may become necessary to move the whole material to a safer site for permanent disposal. This procedure was preferred at 11 sites in the U.S., involving a total of 14.36 million cubic meters of tailings.

To prevent seepage of contaminated water, a liner must be installed below the deposit in many cases, if no natural impermeable layer is present. For this purpose, appropriate lining materials have to be selected. A multi-layer liner may become necessary.
To increase mechanical stability, the following management options may be applied: dewatering of the sludge, smoothing of the slopes, and installation of erosion protection.
On top of the pile, an appropriate cover has to be installed for protection against release of gamma radiation and radon gas, infiltration of precipitation, intrusion of plants and animals, and erosion. This cover in most cases consists of several different layers to meet all requirements.
Moreover, the catchment, collection and treatment of seepage water is necessary to release purified waters to the surface water only. In the long term however, water treatment should no longer be necessary.
Finally, it has to be determined if, and to what extent, contaminated material was used in the surrounding area for construction or landfill purposes. Such contaminated properties should be included in the reclamation program.

 

DISPOSAL OF OTHER MATERIALS

The lack of sites for disposal of toxic and nuclear waste has led to proposals to dump these hazardous wastes in uranium mill tailings piles or in former uranium mines. For example:

• In Thuringia, toxic industrial waste was dumped on top of the Trünzig A tailings pile. In addition, it was planned to cover this toxic waste with an additional 5 meter layer of domestic waste, but this was not realized due to protests of residents.
• On the top of a waste rock pile of the Ronneburg uranium mine in Thuringia, hazardous liquids were dumped, which have to be disposed of, before the pile can be reclaimed.
• In Saxony, scrap contaminated with radioactivity from the shut down Crossen uranium mill is to be dumped in the Helmsdorf uranium mill tailings pile.
• In France, there are discussions to dump industrial low activity radioactive wastes in the uranium mill tailings deposit at l'Écarpière (Loire Atlantique).

If the mixing of uranium mill tailings and other wastes is allowed, then the reclamation of the tailings piles becomes even more difficult, if not impossible, because a best fit method always can be found for a single contaminant only.

• In France 176,150 so called empty casks contaminated with radioactivity were dumped in the open pit of the former Margnac uranium mine near Limoges.
• At the site of the former Bessines uranium mill in the Limousin area (France), the storage of depleted uranium (a waste from uranium enrichment) is planned.
• In the Czech Republic and in Hungary, proposals were made to dump radioactive wastes in former underground uranium mines.

(for details see: Disposal of Other Wastes in Uranium Mines and Mill Tailings)

Former uranium mine and mill sites often have very poor properties for the isolation of contaminants. Detailed investigations have to be performed at such sites by independent experts, before such disposal can be considered.

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.

 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.
 xcvii. The unclassified version of the report can be downloaded in the “Public Documents” section at http://www.dp.doe.gov.
 xcix. Savannah River Site Strategic Plan. http://www.srs.gov