Thermodynamic Analysis on Oxo-acidity of Actinide Oxides for Electrolytic Reduction in Molten Lithium Chloride Salt

Abstract Pyroprocessing is a promising technology for recycling spent nuclear fuel by recovering actinides and reducing radioactive waste. Electrolytic reduction, a key step in pyroprocessing, converts oxide fuels into metals in a molten LiCl–Li₂O electrolyte. This study presents a thermodynamic analysis of actinide oxides to construct potential–oxoacidity diagrams as functions of electrochemical potential and oxide ion activity. Gibbs free energy data were used to analyze reduction pathways for uranium, plutonium, neptunium, americium, and curium. Results show that oxide ion activity significantly influences reduction potential, and actinides exhibit distinct reduction paths. Intermediate oxychloride formation is thermodynamically favored for americium and curium. Estimated cathodic potentials for complete metal formation range from − 3.23 V to − 3.37 V. Although reaction kinetics are not considered, the diagrams offer valuable insight into phase stability and feasible process conditions. This thermodynamic approach provides a useful guideline for optimizing electrolytic reduction conditions and supports future experimental and kinetic investigations.