Monitoring Corrosion and Elemental Contamination in a Molten Li₂O–LiCl Salt During Ten Oxide Reduction Runs of a 0.6 kg-Scale-Simulated Oxide Fuel

Pyroprocessing is an electrochemical fuel-recycling technique that employs a high-temperature molten salt as an electrolyte to process used nuclear fuel. Oxide reduction (OR), which is the initial electrochemical step in pyroprocessing, involves the conversion of oxide fuels into metals in molten LiCl-containing Li₂O. Careful equipment design is required to minimize impurities in the salt, such as corrosion products, for maintaining the long-term efficiency of the OR equipment. In a previous study, we developed OR equipment to reduce 0.6 kg of simulated oxide fuel in 5 kg of Li₂O–LiCl salt and validated its performance over ten consecutive OR runs. This paper presents the chemical analyses of the salt samples taken during each OR run and the precipitate found at the bottom of the crucible after the final run. An inductively coupled plasma-optical emission spectrometer was employed to quantitatively analyze the elemental concentrations in the salt, focusing on the simulated oxide fuel, Pt (OR anode material), and stainless steel (SS, used for the crucible containing salt and cathode basket). The analysis results indicated a linear increase in the concentrations of salt-soluble Sr and Ba over the ten OR runs. In contrast, U and Fe concentrations originating from the SS remained below 400 and 300 ppm, respectively, without a discernible upward trend, whereas other elements were either undetectable or slightly above the detection limit. The precipitate recovered from the crucible contained high concentrations of Pt and Fe, indicating the progressive corrosion of both the Pt anode and SS crucible during the process.