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Abstract
In pyrochemical reprocessing of spent metallic nuclear fuels in a molten salt bath, it is important to recover Cs, significant fission products, with electrochemically negative potentials. In order to develop an electrowinning method, the electrochemical behavior of Cs+ on a solid graphite electrode in the molten FLINAK system (LiF: 49.6mol%, NaF: 14.7mol%, KF: 36.7mol%) was examined by the cyclic voltammetry and the chronopotentiometry. The charge transfer number and the diffusion coefficient for Cs+ were determined by cyclic voltammograms with two kinds of conventional, semi-integral and semi-differential methods and by chronopotentiograms. It was revealed that an irreversible anodic reaction Cs→Cs+ +e− and cathodic reaction Cs+ +e− →Cs on the solid graphite electrode take place in the molten FLINAK system at 773 K. Additionally, the cathodic electrochemical behavior of Cs+ on the liquid Pb electrode in the FLINAK melt was investigated by cyclic voltammetry and chronopotentiometry. It was revealed that an irreversible cathodic reaction Cs++e− →Cs on the liquid Pb electrode takes place in the molten FLINAK system at 773K. In order to examine possibility of recovery of Cs+, we investigate the selectivity on liquid metallic cathodes. We found that Cs are concentrated in the liquid Pb cathode and we can selectively recover Cs on liquid Pb cathode in the molten FLINAK system.
