Hyun Woo Kang

Electrolytic reduction rate of porous UO2 pellets

The electrolytic reduction rate of porous UO2 pellets in a LiCl salt was investigated for various applied charges. The degree of reduction (α) value was evaluated from the ratios of cross-sectional areas of the reduced and oxide parts. An analysis of the experimental results revealed that the first-order reaction model is the best geometry function to describe the reduction reaction. An electrolytic reduction rate equation was proposed using the first-order model, although it was available in a limited region of (0≤α≤0.56). A power law based reaction rate equation was also suggested for the whole range of α, and the reaction time for a complete reduction, estimated using the power law equation, was confirmed through the experimental results. Changes in the Li-Li2O concentration around the reduced pellets for various applied charges were also measured, which increased up to 23 wt% with increasing α.

Electrochemical properties of noble metal anodes for electrolytic reduction of uranium oxide

Noble metals (Rh, Pd, Ir, and Au) were investigated as O2-evolving anodes for electrolytic reduction of UO2 in LiCl–Li2O molten salt to replace Pt anodes, which are gradually consumed owing to Li2PtO3 layer formation. Anodic behaviors of these metals were examined by cyclic voltammetry. Au only showed O2 evolution in a moderate potential range without side reactions, suggesting better electrochemical stability relative to Pt anodes. With Au anodes, UO2 was electrochemically reduced to metallic U. No oxide layer was observed on the surface after the reduction. However, local dissolution remains a potential issue from a stability viewpoint.

Chemical behavior of grey phases in LiCl molten salt for oxide reduction in pyroprocessing

Chemical stabilities of SrZrO3, BaZrO3, and Sr0.5Ba0.5ZrO3 in LiCl molten salt were investigated to evaluate dissolution properties of Sr and Ba in grey phases of spent nuclear fuels during oxide reduction. Sr in SrZrO3 was partially insoluble in LiCl, even in the presence of metallic Li, while Ba in BaZrO3 was almost extracted. In contrast, both Sr and Ba in solid-solution phase (Sr0.5Ba0.5ZrO3) well dissolved in LiCl. Pre-treatment of the spent nuclear fuels before the oxide reduction should be carefully designed to prevent formation of the insoluble Sr-based compounds for efficient Sr separation.