Electrochemical behavior of plutonium in fluoride melt

In the framework of radioactive waste processing, a pyrochemical process for by-products containing plutonium trapped in a CaF₂ matrix is being developed. This process relies on redox reactions occurring in a molten fluoride or chlorofluoride salt at a temperature of 800 to 1000 Celsius degrees. The first step was to determine the thermodynamical properties of plutonium in such a solvent. The experimental results are consistent with theoretical studies and they show that only the solvated specie [Pu(III)] and the metal plutonium [Pu(0)] are stable in experiment conditions and that the reduction of Pu(III) en Pu(0) is done in a single step following the reaction: Pu³⁺ + 3e^- → Pu. These results validate the process, a plutonium solution can be easily reduced by highly electro-negative ions such as calcium ions. (A.C.)