Electrochemical measurements of the corrosion of pure Fe and JLF-1 steel in HF-containing molten FLiNaK salt

Abstract

In order to establish a liquid blanket using a Li-containing molten fluoride salt, the corrosion rate and mechanism of pure Fe and JLF-1 steel in FLiNaK (LiF-NaF- KF = 46.5-11.5-42.0) was investigated by one of the electrochemical methods, the potential step method. Simulating the TF breeding in the blanket, HF gas was injected into FLiNaK at 773 K. The partial pressure of HF gas (pHF) was varied from 8.59 to 2.46 × 103 Pa. The current-potential curves of pure Fe and JLF-1 steel were measured in an electrochemical cell and fit by the Butler-Volmer equation with limited current density. The corrosion current density (icor) of pure Fe increased with pHF as icor=0.6pHF. The corrosion rates of pure Fe and JLF-1 steel were close. In order to keep the uniform corrosion rate of JLF-1 steel below 0.1 mm/year in the blanket, HF concentration in FLiNaK is required less than 1.2 × 10−4 molHF/m3. The cathodic current density (iLc) was proportional to pHF as iLc=-0.11pHF, and, therefore, the rate-limiting process of HF corrosion of pure Fe is predicted to be HF or H+ diffusion in FLiNaK.