Physical-chemical study of the co-extraction of Technetium (VII) and tetravalent metallic elements (Zr,Th,Pu) in the conditions of processing of irradiated fuels

As Technetium is one of the most abundant fission products in irradiated nuclear fuels, this research thesis aims at a better knowledge of the analytic behaviour of Technetium in the Purex process (a liquid-liquid extraction process). The author used a recent physical-chemical theory which allows medium effects to be controlled, and is based on postulates regarding the activity coefficient of a compound in aqueous phase or in an organic phase. The co-extraction of Tc(VI)-M(IV) has thus been studied by modelling reactions in conditions close to that of the industrial reprocessing process. The first part addresses the parameters which allow the medium effect on distribution equilibrium to be controlled (mathematical expression of the activity coefficient). The second part addresses the extraction of nitric acid and metallic nitrates, and the third part the extraction of Technetium VI from nitric solutions. The fourth part deals with the co-extraction of a metallic cation IV - pertechnetate in nitric medium