Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Radioactive metal
Reexamination Certificate
2000-03-03
2001-08-07
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Radioactive metal
C423S021500, C423S157000, C423S181000, C252S184000
Reexamination Certificate
active
06270737
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to extraction agents and methods for selectively recovering cesium (Cs), strontium (Sr), technetium (Tc), rare earth elements, and actinides from aqueous acidic radioactive wastes. More specifically, the invention relates to extraction agent compositions comprising complex organoboron compounds and polyethylene glycol in an organofluorine diluent mixture, and phosphine oxide in a diluent. The invention also provides a method of using extracting and stripping agents to recover cesium, strontium, technetium, rare earth elements and actinides from acidic radioactive wastes.
BACKGROUND OF THE INVENTION
Liquid wastes from nuclear fuel reprocessing are extremely hazardous and expensive to store or dispose of Cesium-137, Strontium-90, actinides, transuranium elements (TRU), rare earth elements, and technetium, which are present in these wastes are of particular concern. The transuranium elements are typically alpha-emitters with very long half-lives, and cesium and strontium are the major heat generators of the waste and produce gamma and beta radiation. Technetium, as the pertechnetate ion, is very mobile in the environment and has an extremely long half life. To increase safe handling of the majority of the waste, and to significantly reduce the storage and/or disposal cost of the waste, it is desirable to partition the waste into two fractions. One containing the majority of the highly radioactive components, and one containing the bulk of the non-radioactive portion of the waste.
Nuclear waste exists in numerous forms and locations world-wide. The largest inventory of highly radioactive materials is produced from the reprocessing of spent nuclear fuel. The fission process produces a number of undesirable, highly-radioactive elements which accumulate in the nuclear fuel. For the reuse or recycling of the unused fissionable material left in the fuel, normally either uranium-235 or plutonium-239, a separation process is employed to partition the fissionable material from the undesirable fission products. This is normally accomplished by leaching or dissolution of a portion or all of the spent nuclear fuel material, followed by chemical separation. Early chemical separation processes were based on precipitation, where, for example, BiPO
4
was used to coprecipitate plutonium for weapons-grade plutonium production. More recently, and by far the most common, solvent extraction processes utilizing tri-n-butyl phosphate are used to chemically separate uranium and/or plutonium from solutions resulting from dissolution or leaching of spent nuclear fuel. The remaining acidic liquid waste, containing the highly radioactive fission products and trace transuranic elements, has been accumulated and stored in various forms around the world for the past 45 years.
Facilities in the United Kingdom, France, Japan, Russia, and China currently use the PUREX process (plutonium-uranium extraction) to recover and purify uranium and/or plutonium. The United States utilized this process (or variations of this process) for commercial-fuel reprocessing at the West Valley Plant, in upstate New York in the 1970's, and for reprocessing of weapons-grade plutonium at the Hanford Site in eastern Washington State, aluminum driver fuel at Savannah River Site in South Carolina, and naval fuel at the Idaho Chemical Processing Plant at the Idaho National Engineering and Environmental Laboratory (INEEL) in eastern Idaho. The reprocessing activities at Hanford were discontinued in the late 1980's and operations at Savannah River and the INEEL were discontinued in the early 1990's. There is currently no active nuclear fuel reprocessing facility in the United States.
There is however, a significant legacy of nuclear waste in storage from previous reprocessing activities. The majority of this waste was neutralized with caustic to facilitate storage in carbon steel vessels (Hanford and Savannah River). At the Idaho Chemical Processing Plant, this waste was calcined in a fluidized-bed calciner at 500° C., producing a granular solid. This solid calcine is stored in stainless steel bins inside concrete vaults. Currently about 4100 m
3
of highly radioactive calcine is stored at the INEEL, and about 1.2 million gallons of acidic liquid waste.
Currently, separate technologies are required for actinides and fission products, and often times, separate processes may be required for specific radionuclides such as cesium, strontium and technetium.
This invention describes novel extraction processes that will readily meet current safety standards and that will effectively separate the above-mentioned radioactive elements from typical nuclear reprocessing wastes. The liquid waste can be effectively decontaminated to meet low-level waste standards in two sequential solvent extraction processes.
U.S. Pat. No. 4,749,518 (Davis et al.) teaches a method for reprocessing nuclear waste by extracting cesium and strontium with crown compounds and cation exchangers.
U.S. Pat. No. 5,603,074 (Miller et al.) teaches a method of recovering cesium and strontium from an aqueous solution using a cobalt dicarbollide derivative.
U.S. Pat. No. 5,666,641 (Abney et al.) discloses a method of recovering cesium and strontium from an aqueous solution with polymeric materials and derivatives of cobalt dicarbollide.
U.S. Pat. Nos. 5,666,642 and 5,698, 169 (Hawthorne et al) teach the extraction of cesium and strontium ions from aqueous solutions, including fission product waste, using substituted metal dicarbollide ions.
To date, the known technologies have focused on recovering cesium and strontium from radioactive active wastes using various solvent systems, and have used the PUREX (plutonium uranium reduction and extraction) process for extracting actinides. However, past technologies have not provided for the selective sequential recovery of cesium, strontium, rare earth elements, technetium and actinides from aqueous acidic radioactive waste, using non-aromatic solvent extracting agents and non-hazardous stripping agents.
SUMMARY OF THE INVENTION
The present invention provides for the selective sequential recovery of cesium, strontium, technetium, rare earth elements and actinides from aqueous acidic radioactive waste, using non aromatic solvent extracting agents and non-hazardous stripping agents.
One embodiment of the invention relates to an extraction agent, for extracting cesium and strontium components from aqueous acidic radioactive waste, comprising a complex organoboron compound and a substituted or unsubstituted polyethylene glycol in an organofluorine diluent mixture.
Another embodiment of the invention relates to the method of selectively recovering cesium and strontium from aqueous acidic radioactive waste comprising:
(a) contacting the aqueous acidic radioactive waste with an extracting agent solution of a complex organoboron compound and a substituted or unsubstituted polyethylene glycol in an organofluorine diluent mixture, to extract cesium and strontium into an organic phase.
Within this embodiment is a method of stripping the cesium and strontium from the extracted organic phase of step (a) comprising:
(b) contacting the organic phase from step (a), containing cesium and strontium, with a strip reagent, such as a nitric acid solution of ammonium nitrate or a nitric acid solution of hexamethylenetetramine, to extract cesium and strontium from the organic phase of step (a), into an aqueous phase.
The Cs and Sr can then be processed by known high level waste (HLW) vitrification processes, or other processes of disposal known to those of skill in the art.
Another embodiment of this invention relates to the method of selectively recovering rare earth elements, technetium and actinides from aqueous acidic radioactive waste comprising:
(c) contacting the aqueous acidic phase from step (a), which contains the rare earth elements, the actinides including U, Pu and Am, technetium, and any other metals present, with an extracting solution of a phosphine oxide in a saturated
Brewer Ken N.
Dzekun Evgeniy G.
Esimantovskiy Vyacheslav M.
Herbst Ronald S.
Law Jack D.
Bos Steven
Caress Virginia B.
Gottlieb Paul A.
The United States of America as represented by the United States
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