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 diisodecylp hosphori c acid (DIDPA) using a battery of 12 centrifugal extractors i nstalled 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 w as added to extract Np effectively. After extraction, Am and Cm were b ack-extracted with 4 M HNO3 in 4 stages and Np and Pu were stripped wi th 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 rec overed in the present experiment, the recovery would be improved to 99 .7 % by increasing the temperature to 45 degrees C, the number of stag es 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 extrac ted and were thus separated from the actinides with high decontaminati on factors. About 98 % of Am and Cm were recovered from the loaded sol vent in the first stripping step with 4 M HNO3. About 86 % of Np and a bout 92 % of Pu were back-extracted with 0.8 M H2C2O4 These incomplete recoveries would be improved by increasing the number of stages and b y optimizing the other process parameters. The present results show th at the centrifugal extractors are applicable to the DIDPA extraction p rocess; small modifications of the extractors would be needed to still improve the extraction of Np and the back-extraction of actinides.