(351c) Design and Operation of Batch Fluoride Salt Purification Systems

Fluoride salts were extensively investigated at Oak Ridge National Laboratory (ORNL) for molten salt reactor (MSR) applications during the 1950’s-1970’s. In these reactor concepts, the fuel is contained the molten salt. Fluoride salts without fuel can also be used as coolants. Recently, there has been a resurgence of interest in MSRs. ORNL has revived and initiated several efforts in molten salt to support the research and development needed to advance MSR technology. Fundamental to these efforts are the ability to produce clean and characterized salt for subsequent research.

Molten fluoride salts are fluxing agents, in that they remove protective oxides scales. To inhibit corrosion, the salt needs to be purified to remove oxygen and moisture. Two facilities have been developed and brought online at ORNL to purify fluoride salts. Both systems are batch processes that utilize HF, H₂, and Ar as the process gases. The large system has been used to clean 160 kg batches of LiF-NaF-KF (FLiNaK) salt within a large nickel crucible. A smaller system has been used to clean a 3.2 kg batch of LiF-BeF2 (FLiBe) salt inside of a graphite crucible. This paper describes the design of these two purification systems and experiences and results from their initial operations.