Environmental Treatment and Immobilization Strategies for Chloride Molten-Salt Wastes from Spent-Fuel Pyroprocessing: A Review

Chloride molten-salt wastes generated during spent-fuel pyroprocessing represent an important environmental and engineering challenge for the sustainable development of closed nuclear fuel cycles. This review summarizes recent advances in the treatment of contaminated process salts arising from electrolytic reduction and electrorefining, with emphasis on waste minimization, salt purification and recycle, radionuclide separation, and final immobilization. The progressive accumulation of fission products, corrosion products, and trace actinide or rare-earth species in LiCl-Li2O and LiCl-KCl salts leads to pronounced hygroscopicity, corrosivity, and compositional complexity, thereby imposing strict requirements on interim storage, process control, and waste-form design. Recent developments in vacuum and reactive distillation, melt crystallization and zone refining, reactive crystallization, and precipitation-based separation are compared in terms of salt recovery, contaminant partitioning, and secondary-waste generation. Two endpoint immobilization strategies are further discussed. The first is direct immobilization, represented by glass-bonded sodalite/chlorosodalite systems, halide-tolerant glasses, phosphate- or aluminosilicate-based matrices, and rapid densification approaches. The second is conversion-based immobilization, in which chloride salts are first dechlorinated or chemically converted prior to vitrification or ceramic consolidation. Finally, future priorities are identified, including engineering-scale validation, efficient halogen capture from off-gas streams, minimization of secondary wastes, and standardized durability evaluation for multicomponent waste forms. This review highlights that the safe treatment and immobilization of chloride molten-salt wastes are essential for improving the environmental acceptability and sustainability of advanced nuclear-energy systems.