[3L10-12] Blanket Materials

[3L11] Electrochemical analysis on corrosion mechanisms for structural materials in molten FLiNaK salt containing hydrogen fluoride

*Gaku Yamazaki¹, Takuya Nagasaka^1,2, Juro Yagi³, Takuya Goto⁴, Teruya Tanaka^1,2, Takashi Watanabe⁵, Akio Sagara^1,2 (1. SOKENDAI, 2. NIFS, 3. Kyoto Univ., 4. Doshisha Univ., 5. UEC)

Keywords:molten salt blanket, FLiNaK, hydrogen fluoride, corrosion, electrochemistry

Structural materials’ corrosion by hydrogen fluorides determines the lifetime of molten salt blankets. This study estimates corrosion mechanisms in a blanket environment (around 1 molHF/m³), based on electrochemical measurements in molten FLiNaK (LiF-NaF-KF=46.5:11.5:42.0) salt containing 1-10 mol/m³ of hydrogen fluoride (HF) besides the previous one, 100 mol/m³.
Pure iron, the main element of reduced activation ferritic martensitic steels, was immersed into FLiNaK at 500℃ to obtain current-potential relationship.
Corrosion rate at the immersed potential increased with the HF concentration. Cathodic limited current was proportional to the HF concentration, which is explained by the Fick’s 1^st law with constant diffusion coefficient. Rate-limiting corrosion process is, therefore, estimated to be HF diffusion in the boundary layer of FLiNaK on iron surfaces.