Actinide partitioning by HDEHP solvent extraction. A verification of the process scheme by counter-current experiments in hot cells

Abstract

Three HAW partitioning processes have been selected and investigated on a laboratory scale at the JRC-Ispra Establishment (CEC). The purpose of these processes was to demonstrate the chemical feasibility of the actinide separation from HAW in order to reduce the potential long term hazard of virtified HAW. Two of these processes (HDEHP and TBP processes) are based on liquid-liquid extraction of actinides from original and concentrated HAW solutions, respectively. To verify a larger fully active scale these two process flow sheets, a fruitful collaboration was established between the JRC (Ispra Establishment) and the CEA (CEN-Fontenay aux Roses, France). For this purpose, on the basis of indications resulting from the previous laboratory investigations at the JRC, continuous countercurrent experiments with mixer-settler batteries were performed in the hot cells of CENFAR laboratories. As a feed solution a fully active HAW raffinate prepared by treatment of high burnt UO 2 fuel specimens (33 GWd/tU) was used. The present paper deals with the verification of option 1 of the HDEHP process flow sheet and illustrates related experimental results. By means of MS batteries continuous countercurrent operating conditions were thus applied to the most relevant steps of the HDEHP 1 process scheme, namely: actinide (U, Pu, Np, Am, Cm) extraction from HAW; trivalent actinides (Am, Cm) back-extraction from loaded HDEHP, with the aim of verifying the performances and hydraulic behaviour of these two specific process steps under dynamic conditions. For the remaining process steps (RE and Pu back-extractions, exhausted solvent clean-up) experiments were carried out batch wise. The reduction of the HAW acidity (denitration) was successfully operated on fully active and rather large (42 litres of HAW) scale according to the experimental conditions indicated by additional exploratory experiments, performed at Ispra. Data on the HAW denitration will be presented with particular reference to the problem of the precipitation of actinides during this process. A preliminary indication is also given of the areas of the HDEHP 1 process scheme where further experimental investigations are needed.