Electrochemistry in molten LiF-BeF2 salt for fluoride salt-cooled high temperature reactor applications

Abstract

A dynamic beryllium reference electrode has been developed for in situ electrochemistry studies of molten LiF-BeF2 (66-34 mol%) (FLiBe) salt which is being considered as the primary coolant for the fluoride salt-cooled high temperature reactor (FHR). Measurement and control of the salt redox potential can mitigate corrosion which is an important challenge in high temperature molten fluoride salts. This three electrode probe has demonstrated good reproducibility in the measurement of the salt’s redox potential with an error of ±4 mV at 500 °C. The response of the probe to changes in salt chemistry was investigated by the intentional additions of fluorides of nickel, iron, and chromium, which are corrosion products of common structural materials. The equilibrium potentials of these metal impurity fluorides were measured in solutions containing approximately 250 ppm of each impurity using cyclic voltammetry. This approach is being extended to study electrochemical purification of molten FLiBe.