Electrochemical Techniques to Monitor the Concentration of Oxide in Molten FLiNaK Salt

Molten fluoride salts have attracted interest as fuel and/or coolant for several different molten salt reactor (MSR) designs. Fluoride salts have many advantageous properties for these applications, such as high ionic conductivity, good heat transfer capacity, and high solubility for actinides. However, the impurities of the fluoride salt corrode the metals of MSR such as H₂O, HF, and metal impurities. Therefore, it is important to monitor the oxides in molten fluoride salt. In this study, LiF-NaF-KF (FLiNaK) salt was used as a less toxic surrogate for FLiBe because of the toxicity of beryllium. In this work, we focused on measuring the concentration of oxide by adding Li₂O in the FLiNaK salt using two electrochemical methods: cyclic voltammetry (CV) and square waver voltammetry (SWV). Moreover, after the electrochemical tests, the salts were analyzed for concentration of oxygen by LECO in order to compare with electrochemical results. We observed an oxidation peak corresponding to oxide using CV with a tungsten working electrode. Then SWV was used to measure the oxidation peak for oxide at various concentrations (0.1 to 2.0 wt.% of Li₂O). SWV can measure the low concentration, because SWV is more sensitive to the oxidation current than CV through eliminating the non-faradaic current.