Deliquescence of Eutectic LiCl-KCl Diluted with NaCl for Interim Waste Salt Storage

Abstract

Molten eutectic LiCl-KCl salt is a widely used electrolyte for electrorefining uranium from spent nuclear fuel. Due to the hygroscopic nature of this salt, such operations must be performed under controlled atmospheric conditions, and waste salts require careful storage to avoid deliquescence and corrosion of container materials. This study investigated a potential processing path for reducing the degree of deliquescence through dilution to varying extents with NaCl. The hydration behavior of LiCl-KCl salts diluted with NaCl was evaluated in terms of mass gain due to water absorption, degree of deliquescence (including first appearances of standing water), and evidence of corrosion to stainless steel containers in a humid air environment (40°C, 20% relative humidity). In this humid air environment, pure eutectic LiCl-KCl exhibited a 50 mass % increase due to water absorption and showed evidence of standing water after 24 h. Waste salt diluted with NaCl required loadings of 89 mass % NaCl in order to prevent deliquescence and exhibited a 3 mass % increase due to water absorption. After periodic observation for 48 h, standing water was observed near all ingots with the exception of the 89 mass % NaCl samples. Dilution with 89% NaCl was also found to reduce evidence of corrosion when stored in stainless steel crucibles. While dilution with NaCl greatly decreases steady-state hydration, the storage volume is increased ~10× through this procedure.

Keywords:

• Electrochemical processing
• electrorefiner salt
• eutectic LiCl-KCl
• waste salt, deliquescence

Acknowledgments

This work was supported by Idaho National Laboratory under standard subcontract no. 232632 and performed under the auspices of the U.S. Department of Energy Fuel Cycle Research and Development Program under the direction of Dr. Michael Patterson, project manager for the EBR-II spent fuel treatment project. Idaho National Laboratory is operated by Battelle Energy Alliance, LLC under contract no. DE-AC07-05ID14517. The authors would like to thank Michael Shaltry for input on the salt compositions and hydration studies.