(259a) Continuous Monitoring of Ni Corrosion in Eutectic LiCl-KCl-UCl3 Using High Temperature Voltammetry

Pyrochemical reprocessing in molten chloride is a leading technology option for the reprocessing of used nuclear fuel. This process includes several high temperature (773 K or higher) unit operations, including electrorefining. Electrorefining separates U or U/TRU from the used fuel via electrodeposition on a cathode using a molten LiCl-KCl-UCl₃ electrolyte. Stainless steel is the preferred candidate material for the materials of construction in an electrorefiner in contact with the molten salt. To better understand the potential for corrosion of stainless steel in an electrorefiner, electrochemical experiments were performed with Ni in contact with LiCl-KCl-UCl₃, while varying concentrations of H₂O vapor were bubbled into the salt. The water vapor varied from 20 to 950 ppm in argon and was bubbled into the salt using a ceramic tuyere at 773 K. Electrochemical measurements such as open circuit potentiometry and cyclic voltammetry were used to monitor the reactions occurring in the molten salt in near real time and real time, respectively. Evidence of oxidation of Ni to NiCl₂ was observed in addition to precipitation of uranium from the salt via reaction with water to form oxides. Conclusions will be presented regarding the maximum allowable moisture concentration in the cover gas for the electrorefiner to prevent stainless steel corrosion. Consequences of accidental ingress of air into a pyrochemical reprocessing facility will also be discussed.