Solvent extraction processes in the nuclear fuel cycle

Solvent extraction has been the major technique in treatment of spent nuclear fuel to separate unburnt uranium and plutonium from fission products. Methylisobutylketone (MIBK), used initially, was soon replaced by PUREX which uses tributylphosphate as the extractant of UO22+ and Pu4+ from the fission products. PUREX remains the treatment method used internationally. Additional separations are used after PUREX to further separate U and Pu or to recover some of the fission products. TRUEX uses CMPO (octyl(phenyl))-N, N-dibutylcarbamoylmethylphosphine oxide) to further purify Pu and U from the fission products. In TRAMEX trialkylamines or tetraalkylammonium salts in organic solvents provide a high selectivity in separation of tri- and tetravalent actinides from Ln(III) and other fission products. The DIAMEX process uses a diamide to extract the transuranium elements efficiently. Processes such as SREX (for Sr(II) removal), DICARBOLLIDE (for Cs(I) and/or Sr(II removal) and BoBCalixC8 are also discussed.