Effect of alkali and alkaline-earth chloride addition on electrolytic reduction of UO2 in LiCl salt bath

The electrolytic reduction process of actinide oxides in a LiCl salt bath at 923 K has been developed for nuclear fuel reprocessing. Since some salt-soluble fission products, such as Cs, Sr and Ba, accumulate in the LiCl salt bath, their effect on UO2 reduction was investigated. In the experiments, UO2 specimens were reduced by potential- or current-controlled electrolysis in various LiCl salt baths containing up to 30 mol% of KCl, CsCl, SrCl2 or BaCl2. The rate of UO2 reduction in a LiCl salt bath was considerably decreased by the addition of alkali metal chlorides (KCl and CsCl) and slightly decreased by BaCl2 addition. SrCl2 addition had no appreciable effect. It was suggested that the diffusion of O2− ions from the inside of UO2 specimens to the bulk salt determined the reduction rate during the electrolysis and that the effect of salt composition was related to the solubility of O2− ions in the salt bath.