Abstract
Solvent extraction models as the ones developed by the CEA required a precise description of extraction equilibria taking into account explicitely the deviation from ideality and the speciation of the different elements involved. Firstly, binary data acquisition of ruthenium nitrosylnitrate, problematic electrolyte in the Purex process, for the determination of the deviation from ideality has been performed for water activity between 1 and 0.750. The chemical properties of this electrolyte required the development of new methodologies to adapt the simple solution approach to mixtures exhibiting a deviation from this behavior. Secondly, nitric acid speciation in the organic phase, required to determine the quantity of free TBP in solution, has been studied throught the analysis of experimental data two different systems : TBP/HNO3/H2O/TPH and TBP/HNO3. The highlighting of the importance of water for the formation of clusters observed experimentally allows the proposition of a model depending on the concentration of nitric acid in the organic phase.