PUREX process Plutonium Uranium Redox

In order to separate the uranium and plutonium the Pu022+ was reduced to Pu3+, which was not extracted by MIBK and was thus held in the aqueous phase. The choice of a reducing agent for plutonium is rather important, and is discussed in more detail below in relation to the Purex process. In the Redox process, 0.05 M aqueous iron(II) sulfamate salted with 1.3MA1(N03)3 was used, the reduction of Pu022+ by Fe2"1" proceeding according to equation (156). The products... 

Some countries, e.g., France, Japan, Russia, and the United Kingdom have chosen to reprocess their spent nuclear fuel to recycle uranium and plutonium as nuclear fuel and to obtain a high active waste (HAW) firaction that is less radiotoxic than the spent fuel itself. In this process, very high separation factors are necessary. The fission product activity has to be reduced by a factor of > 10 and the separation factor between uranium and plutonium must be at least 2 x lO. All full-scale reprocessing processes are based on solvent extraction, and today the plutonium uranium redox extraction (PUREX) process dominates the market completely. 

In the case of a fast neutron spectrum, MOX fuel has been proposed by Oka et al. (2010) with an average concentration of fissile plutonium of approximately 20%. Such fuel can be produced from recycling spent fuel of LWRs with the Plutonium Uranium Redox Extraction (PUREX) process, a mature fuel cycle technology. 

Redox [Reduction oxidation] A process for separating the components of used nuclear fuel by solvent extraction. It was the first such process to be used and was brought into operation at Hanford, WA, in 1951, but was superseded in 1954 by the Purex process. The key to the process was the alternate reduction and oxidation of the plutonium, hence the name. The solvent was Hexone (4-methyl-2-pentanone, methyl wobutyl ketone), so the process was also known as the Hexone process. The aqueous phase contained a high concentration of aluminum nitrate to salt out the uranium and plutonium nitrates into the organic phase. The presence of this aluminum nitrate in the wastes from the process, which made them bulky, was the main reason for the abandonment of the process. See also Butex. 

Reduction and oxidation (redox) steps are major process steps in the Purex process. Use is made of redox reactions to alter the valency of plutonium, uranium or neptunium with the object of producing these metals with a high degree of purity. 

The aim of the present improvement work on the PUREX process is to make the separations more selective and to create effluent streams of high purity. Thus, modifications are performed to make neptunium end up in a fraction for later transmutation in a reactor or accelerator-driven system. This can be achieved by a better control of redox conditions in the process. Today neptunium is partially co-exlracted with plutonium and uranium. There are also suggestions to withdraw product streams with Tc and respectively, i.e., long-lived nuclides that might be of interest for transmutation. 

The photochemical reduction of a solution containing both uranium(VI) and plutonium(IV) is also of interest for reprocessing applications. Early experiments (12a) showed a significant reduction of plutonium(IV) by light in Purex-type process solutions. Since the quantum yield for plutonium redox reactions is about one-tenth that for uranyl reduction (7b,c) the most likely path of plutonium(IV) reduction in these experiments appears to have been by uranium(IV) or uranium(V) generated by photochemical reduction of uranyl by other components of the solutions. Further experiments in this area would be useful. 

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