Actinide partitioning from HLW in a continuous DIDPA extraction process by means of centrifugal extractors

An experiment on actinide partitioning from real high level waste (HLW) was performed in a continuous process by extraction with diisodecylphosphori c acid (DIDPA) using a battery of 12 centrifugal extractors installed in a hot cell. The HNO3 concentration of the HLW was adjusted to 0.5 M by dilution. The extraction section had 8 stages, and H2O2 was added to extract Np effectively. After extraction, Am and Cm were back-extracted with 4 M HNO3 in 4 stages and Np and Pu were stripped with 0.8 M H2C2O4 in 8 stages. The actinides, except Np, were extracted from HLW with a very high yield. Although only 84 % of the Np were recovered in the present experiment, the recovery would be improved to 99.7 % by increasing the temperature to 45 degrees C, the number of stages from 8 to 16 and the H2O2 concentration from 1 M to 2 M. Long-lived Tc and the main heat and radiation emitters Cs and Sr were not extracted and were thus separated from the actinides with high decontamination factors. About 98 % of Am and Cm were recovered from the loaded solvent in the first stripping step with 4 M HNO3. About 86 % of Np and about 92 % of Pu were back-extracted with 0.8 M H2C2O4 These incomplete recoveries would be improved by increasing the number of stages and by optimizing the other process parameters. The present results show that the centrifugal extractors are applicable to the DIDPA extraction process; small modifications of the extractors would be needed to still improve the extraction of Np and the back-extraction of actinides.