Recovery of minor actinides from HLLW using the DIAMEX process

Abstract

Summary: In this work a hot demonstration of the DIAMEX process using the new reference molecule DMDOHEMA (N,N^′-DiMethyl-N,N^′-DiOctylHexylEthoxyMalonAmide) and genuine high-level PUREX raffinate as feed is reported. The continuous counter-current experiment was carried out in a 16-stage centrifugal extractor battery, installed in a hot cell. In order to produce a representative High Level Liquid Waste (HLLW) a PUREX process was applied on dissolved fuel using the same equipment. It was demonstrated that 5 extraction stages were sufficient to achieve feed decontamination factors above 2200 and 320 for Am and Cm, respectively. Co-extraction of molybdenum and zirconium, as well as of palladium, were efficiently prevented using oxalic acid and HEDTA scrubbing, respectively. However, technetium, yttrium, and to some extent ruthenium, were co-extracted. The back-extraction proved to be very efficient, yielding in 4 stages more than 99.9% recovery of Am and Cm. The extraction profiles were modeled with computer code simulations and the results compared with data obtained from an experiment using the former reference molecule DMDBTDMA (DiMethylDiButylTetraDecylMalonAmide).