Development of the pyrochemical DOS process for the recovery of actinides and its application for reprocessing of transmutation fuel targets

Abstract : Pyrochemical technology using high-temperature molten salts and molten metal media presents a potential interest for an overall separation and transmutation strategy for long-lived radionuclides. Within the frame of the two French acts on radioactive waste management, a pyrochemical RandD program was launched at the CEA Marcoule in the late 90's. The developed so called DOS (Direct Oxide Solubilisation) process, based on a two- step liquid-liquid (molten salt/liquid metal) extraction, aims to demonstrate the feasibility of a group separation of actinides with sufficient decontamination from fission products.The first step consists of a selective reductive extraction of actinides coming from direct dissolution of oxide fuel in the molten fluoride salt, into liquid aluminium metal. The second step is the actinides back-extraction, which consists of a liquid/liquid oxidative stripping of the An from aluminium matrix into molten chloride media. The DOS process has been successfully demonstrated for treatment of oxide type fuels within the last years the core of the process has been already assessed and the studies have shown high selectivity and a quantitative recovery of actinides. Within the framework of the SACSESS European research program, the present work focuses on a potential application of the DOS process for the reprocessing of MgO based CERCER transmutation targets. The behaviour of Mg was investigated regarding the solubility of MgO in the fluoride salt and then regarding Mg reductive extraction in metallic Al. The impact of Mg on the efficiency of An reductive extraction was also studied using U3O8 simulating the behaviour of MA oxides. Eventually, the validity of the DOS process was demonstrated on a Pu0.5Am0.5O2-et61540;-MgO FUTURIX CERCER pellet synthesized at the ATALANTE facility within the framework of Eurotrans program. Substantial amount of Nd2O3 was added during the demonstration experiment in order to simulate fission products behaviour. Quantitative recovery of purified Pu and Am was achieved in a single batch experiment.