First demonstration of a centrifugal solvent extraction process for minor actinides from a concentrated spent fuel solution

The efficiency of minor actinides (MA) recovery in the diamide extraction (DIAMEX) process has already been demonstrated using high active raffinate (HAR). In view of an industrial application, the next development step aims at the partitioning of MA from high active concentrate (HAC) as feed. The volume reduction reduces the size of the installation, and thereby the amount of waste and the costs of the process. In this work, MA recovery by DIAMEX partitioning using genuine HAC has for the first time been demonstrated. The experiment was successfully carried out in a 16-stage centrifugal extractor battery, installed in the hot cell facilities at ITU, using N,N′-dimethyl-N,N′-dioctyl-2-(2-(hexyloxy)ethyl)-malonamide (DMDOHEMA) as extractant. In order to produce a representative HAC, a concentration-denitration process was applied to a genuine HAR solution produced by small scale plutonium uranium redox extraction (PUREX) reprocessing of a mixed oxide (MOX) fuel solution. In the DIAMEX process, five extraction stages were sufficient to achieve feed decontamination factors above 10,000 for Am and Cm. Co-extraction of molybdenum, zirconium and palladium was prevented using oxalic acid and HEDTA scrubbing. The back-extraction proved to be very efficient, yielding in four stages recoveries for Am and Cm in the product fraction above 99.7 and 99.9%, respectively, which can be further improved by process flowsheet optimisation. This work is a major contribution in the field of partitioning and an important step towards the industrial implementation of MA partitioning.