Plutonium uranium reduction extraction tributyl phosphate

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. 

Then the fuel elements are dissolved in 7m HNO3 to give a solution containing U and Pu which, in the widely used plutonium-uranium-reduction, or Purex process, are extracted into 20% tributyl phosphate (TBP) in kerosene leaving most of the fission products... 

Reprocessing is based on liquid-liquid extraction for the recovery of uranium and plutonium from used nuclear fuel (PUREX process). The spent fuel is first dissolved in nitric acid. After the dissolution step and the removal of fine insoluble solids, an organic solvent composed of 30% TriButyl Phosphate (TBP) in TetraPropylene Hydrogenated (TPH) or Isopar L is used to recover both uranium and plutonium the great majority of fission products remain in the aqueous nitric acid phase. Once separated from the fission products, back-extraction combined with a reduction of Pu(I V) to Pu(III) allows plutonium to be separated from uranium these two compounds can be recycled.2... 

Some part of the spent fuel of atomic reactors is reprocessed separating uranium, plutonium, and the fission products, in order to produce new fissionable fuel or to collect some part of the valuable fission products. While several reprocessing methods have been proposed, the Purex process is the most widely used all over the world. The process uses 30% tributyl phosphate, TBP, as extractant in dodecane or kerosene solvent that is used to decrease the viscosity and the density of the liquid. The mixture is easily separated from water. The spent fuel is dissolved in concentrated nitric acid and the aqueous solution is mixed with the organic extractant. U and Pu present in the aqueous phase in the forms U02 and Pu are extracted to the organic phase, the fission products remain in the aqueous solution. After reduction of Pu by chemical or electrochemical method, Pu goes back to the aqueous phase, while the uranium remains in the organic phase (Benndict et al., 1981 Choppin et al. 1995 Katsumura 2004). 

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