Electrochemical impedance spectroscopic study on Eu2+ and Sr2+ using liquid metal cathodes in molten chlorides

Abstract

For the pyrochemical reprocessing of spent metallic nuclear fuels in molten salt baths it is important to investigate the behavior of the electrochemically negative elements Eu and Sr, which are significant fission products. Voltammetric and chronopotentiometric studies have shown that the reduction of Eu2+ and Sr2+ on liquid Pb cathodes in molten chloride baths at 1073 K follows the alloy formation reaction: Eu2+ + 2e- + 3Pb → EuPb3 and Sr2+ + 2e- + 3Pb → SrPb3. In the present work these alloy formation reactions were studied by electrochemical impedance spectroscopy. Analysis of the spectra showed that the electronic exchange of Eu2+/Eu and Sr2+/Sr is quasi-reversible. Moreover, the experimental results allowed the determination of the kinetic parameters of Eu2+/Eu and Sr2+/Sr, the diffusion coefficients of these species in molten chloride baths, and also the diffusion layer thickness.