Basic fundamental research on chromium-coated cladding for improved accident tolerance, 2; Electrochemical measurement of Cr in high temperature water under gamma-ray irradiation environment

Ishijima, Yasuhiro ; Soma, Yasutaka   ; Sato, Tomonori  ; Yamashita, Shinichiro   ; Igarashi, Takahiro  

Chromium-coated claddings are strong candidates for accident tolerant fuel (ATF) owing to the excellent corrosion resistance of chromium (Cr) in high-temperature steam, attributed to the stability of a Cr(III) passive film. In high-temperature water, however, oxidative species can oxidize Cr to soluble Cr(VI), increasing the corrosion potential and inducing trans-passive corrosion that may degrade coating integrity. The corrosion behavior of Cr under irradiation in such environments remains unclear, limiting the assessment of Cr coating performance in light water reactors (LWRs). Electrochemical measurements in autoclaves are commonly employed to investigate corrosion mechanisms, but technical challenges arise under irradiation, including degradation of signal line insulation and increased noise due to long cables and small specimen size. To overcome these limitations, we developed an autoclave system specifically designed for gamma-ray irradiation experiments. The system enables electrochemical measurements of Cr in high-temperature water under irradiation conditions simulating an LWR environment. Preliminary confirmation tests demonstrated stable acquisition of electrochemical signals, verifying the feasibility of the system.