(259c) Effect of LiOH Contamination on the Electrolytic Reduction of Spent Oxide Fuel in Molten LiCl-Li2O

Spent oxide fuel must be reduced to metallic form prior to electrorefining. In the oxide reduction process, spent UO₂ based fuel is contained in a stainless steel cathode basket and immersed into an electrochemical cell containing a LiCl-Li₂O melt at 650^oC, at which point oxide reduction can be achieved via direct electrolytic reduction (DER) of oxides with simultaneous evolution of O₂ gas at the anode. Both Li₂O and UO₂ can be reduced in the cathode basket. Lithium metal formed from reduction of Li₂O will spontaneously reduce UO₂, so the net result is the same. However, moisture contamination in the salt results in the formation of LiOH, which interferes with the reduction of UO₂ and Li₂O and decreases current efficiency. LiOH reduction occurs at a less cathodic potential than does Li₂O or UO₂. In this study, the impact of moisture and LiOH on the oxide reduction process and the effect of contamination removal methods were investigated. Thermogravimetric analysis (TGA) was used to measure moisture content in salts. Reduction peaks in cyclic voltammetry (CV) scans were associated with the presence of LiOH in the salt. It was found that LiOH could be removed from the salt via addition of Li metal or electrochemically through chronopotentiometric methods. Development and optimization of a salt cleanup process will be discussed as an important requirement to efficiently running DER of spent oxide fuel.