Solvent extraction irradiated nuclear fuels

The solvent extraction process that uses TBP solutions to recover plutonium and uranium from irradiated nuclear fuels is called Purex (plutonium uranium extraction). The Purex process provides recovery of more than 99% of both uranium and plutonium with excellent decontamination of both elements from fission products. The Purex process is used worldwide to reprocess spent reactor fuel. During the last several decades, many variations of the Purex process have been developed and demonstrated on a plant scale. 

Uranyl nitrate has an unusual property, shared only by nitrates of a few other actinides, of being very soluble in a number of organic solvents. When such an organic solvent is immiscible with water, it can be used in a solvent extraction process to extract uranium from aqueous solutions and separate it from associated impurities. Such applications of solvent extraction are very important in extracting and purifying uranium from leach solution of uranium ores or from nitric acid solution of irradiated nuclear fuel. Examples of extractants that have been used for such separation processes are listed in Table 5.14. 

Naylor, A. and Wilson, P. D. 1983. Recovery of uranium and plutonium from irradiated nuclear fuel. In Handbook of solvent extraction, eds. T. C. Lo, M. H. I. Baird, and C. Hanson, 768-798. New York John WUey Sons. 

TBP is a well-known extractant on many solvent extraction processes in the nuclear fuel processing industry. TBP has been an excellent all-around solvent for the reprocessing of irradiated nuclear fuel. It possesses all major requirements that extractants must have to be successfully applied in an industrial solvent extraction separation process. These properties have been also transferred to the solid polymeric extractant TVEX-TBP. 

Nuclear Waste. NRC defines high level radioactive waste to include (/) irradiated (spent) reactor fuel (2) Hquid waste resulting from the operation of the first cycle solvent extraction system, and the concentrated wastes from subsequent extraction cycles, in a faciHty for reprocessing irradiated reactor fuel and (3) soHds into which such Hquid wastes have been converted. Approximately 23,000 metric tons of spent nuclear fuel has been stored at commercial nuclear reactors as of 1991. This amount is expected to double by the year 2001. 

The effect of irradiation on the extractability of sulfoxides towards plutonium, uranium and some fission products were studied by Subramanian and coworkers . They studied mainly the effect of irradiation on dihexyl sulfoxide (DHSO) and found that irradiation did not change the distribution coefficient for Ru, Eu and Ce but increases the distribution coefficient for Zr and Pu. When comparing DHSO and tributyl phosphate (TBP), the usual solvent for the recovery and purification of plutonium and uranium from spent nuclear fuels, the effect of irradiation to deteriorate the extraction capability is much larger in TBP. Lan and coworkers studied diphenyl sulfoxides as protectors for the gamma radiolysis of TBP. It was found that diphenyl sulfoxide can accept energy from two different kinds of excited TBP and thus inhibits the decomposition of the latter. 

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