Plutonium Uranium Reduction Extraction purification

The Purex process, ie, plutonium uranium reduction extraction, employs an organic phase consisting of 30 wt % TBP dissolved in a kerosene-type diluent. Purification and separation of U and Pu is achieved because of the extractability of U02+2 and Pu(IV) nitrates by TBP and the relative inextractability of Pu(III) and most fission product nitrates. Plutonium nitrate and U02(N03)2 are extracted into the organic phase by the formation of compounds, eg, Pu(N03)4 -2TBP. The plutonium is reduced to Pu(III) by treatment with ferrous sulfamate, hydrazine, or hydroxylamine and is transferred to the aqueous phase U remains in the organic phase. Further purification is achieved by oxidation of Pu(III) to Pu(IV) and re-extraction with TBP. The plutonium is transferred to an aqueous product. Plutonium recovery from the Purex process is ca 99.9 wt % (128). Decontamination factors are 106 — 10s (97,126,129). A flow sheet of the Purex process is shown in Figure 7. 

Many variants of the Purex (Plutonium Uranium Reduction Extraction) process23S based on TBP extraction have been developed but a basic outline flowsheet is illustrated in Figure 38. This shows the so-called early split flowsheet most commonly used in existing plants. It involves the separation of the uranium and plutonium using two different back-extractant streams during the first solvent extraction cycle. Additional solvent extraction cycles are then carried out independently on the uranium and plutonium streams to effect further purification. An alternative arrangement is the iate split flowsheet used at the Cap La Hague plant in France, and the... 

The control of the actinide metal ion valence state plays a pivotal role in the separation and purification of uranium and plutonium during the processing of spent nuclear fuel. Most commercial plants use the plutonium-uranium reduction extraction process (PUREX) [58], wherein spent fuel rods are initially dissolved in nitric acid. The dissolved U and Pu are subsequently extracted from the nitric solution into a non-aqueous phase of tributyl phosphate (TBP) dissolved in an inert hydrocarbon diluent such as dodecane or odourless kerosene (OK). The organic phase is then subjected to solvent extraction techniques to partition the U from the Pu, the extractability of the ions into the TBP/OK phase being strongly dependent upon the valence state of the actinide in question. 

The plutonium purification may be achieved by additional TBP extraction cycles. U(IV) cannot be used as reductant in this part of the process. The final uranium and plutonium products are nitrate solutions whose conversion to oxides, fluorides, etc., have been described earlier ( 5.5.3). 

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