Use of a mixture of TRPO and TBP for the partitioning of actinides from high-level waste solutions of PUREX origin and its comparison with CMPO and other phosphorus-based extractants

The partitioning of long-lived alpha-emitting actinides, present in high-level radioactive waste (HLW) solutions from PUREX reprocessing of spent nuclear fuels, has been carried out using a commercially available, reasonably inexpensive, trialkylphosphine oxide (TRPO), Cyanex(R)-923 alone or its mixture with tri-n-butylphosphate (TBP) in dodecane. The studies have been carried out from nitric acid as well as from three types of synthetic HLW solutions. With 30% TRPO alone, third-phase formation was observed when HLW in 3.0 M HNO3 was taken as such. With the mixture of TRPO and TBP, it has been shown that the HLW need not be diluted 10 times, but only the acidity has to be reduced from similar to3 to similar to1 M (without substantial dilution) to achieve an efficient separation of the minor actinides. The results thus obtained using TRPO has been compared with those already reported while using dihexyl-N,N-diethylcarbamoylmethyl phosphonate, diisodecyl phosphoric acid, and octyl(phenyl)N,N-diisobutylcarbamoylmethyphosphine oxide (CMPO). The mixture of 0.2 M CMPO and 1.2 M TBP in dodecane (TRUEX solvent) seems to be a superior extractant for the partitioning of minor actinides from HLW solutions.