Electrolytic Reduction and Electrorefining of Uranium to Develop Pyrochemical Reprocessing of Oxide Fuels

Abstract

Two series of pyrochemical reprocessing tests for oxide fuels, consisting of pretreatment, electrolytic reduction, and electrorefining processes, were conducted using ~100 g of UO2. In the pretreatment process, UO2 pellets of the starting material were oxidized into U3O8 powder, which simulated fuel decladding by voloxidation. Then, UO2 sinter with a porosity of 30 to 38% was fabricated from the U3O8 powder. Two cathode baskets charged with ~100 g of the UO2 sinter were prepared, and two electrolytic reduction tests were carried out in a LiCl-Li2O electrolyte at 650°C. The results suggested that the reduction to uranium metal could be completed within 10 h with the current efficiency >62%. It was verified that the porous UO2 sinter was of great advantage to the electrolytic reduction process. In the subsequent electrorefining process, the reduction products were charged in two anode baskets, and electrolysis was carried out in a LiCl-KCl-UCl3 electrolyte at 500°C. Within 8 h, most of the uranium metal was anodically dissolved into the electrolyte with the current efficiency >88%. Dendritic uranium metal was collected on a stainless steel cathode. Consequently, it was demonstrated that a refined uranium metal could be produced from UO2 pellets with a high degree of efficiency.