Investigation of dissolution behavior of SrO in molten LiCl-KCl salts for heat reduction of used nuclear fuel

90Sr is one of the most heat-generating fission products in used nuclear fuel. Because of its chemical stability as an oxide, it is tricky to separate Sr from used nuclear fuel without separating nuclear materials. Here we report on thermodynamic behavior of one of the primary contributors of decay heat, SrO, by investigating the reactions in molten salt systems. We study the respective influences of the KCl molar fraction and temperature on the dissolution behavior of SrO in molten LiCl-KCl salts: a widely used-salt composition owing to its low melting point and wide electrochemical window. Our results reveal that the solubility of SrO is relatively low in the eutectic LiCl-KCl at 773 K, compared to the other temperatures (823 K to 923 K) and the solubility decreased with increasing molar fraction of KCl (0 to 0.6) in LiCl at 923 K. Sr4OCl6 is produced by the dissolution of SrO in LiCl-KCl, and was confirmed by applying X-ray analyses. The results can be utilized to design a molten salt leaching process to separate high heat-generating fission products without proliferation issues, thereby reducing the environmental footprint during final waste disposal. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the thermodynamic behavior of SrO in molten salt systems and finds that its solubility is relatively low in the eutectic LiCl-KCl. These results can be used to design a molten salt leaching process for separating high heat-generating fission products and reducing environmental impact during final waste disposal.