Corrosion behavior of pre-oxidized HR-224 superalloy in supercritical water environment at 700 °C

Corrosion of cladding materials in supercritical water (SCW) environment is a key reliability issue for the safety of nuclear power plant. In this study, we propose to use the pre-oxidized treatment to provide better corrosion resistance of cladding materials in the SCW environment. The nickel-based superalloy HR-224 was first pre-oxidized in flowing air at 982 °C for 100 h to establish a continuous and dense scales and then exposed in the SCW environment with high oxygen content (8.3 ppm) at 700 °C and 24.8 MPa for cyclic oxidation testing up to 1300 h. The pre-oxidized samples exhibit better corrosion resistance than as-received samples in the SCW environment. After pre-oxidizing process, triple scales, Ni(Cr, Fe)₂O₄ spinel/Cr₂O₃/α-Al₂O₃ were observed, and the growth of inner α-Al₂O₃ layer is predominant in the SCW environment. The α-Al₂O₃ layer in pre-oxidized samples was found to effectively decrease outward migration of metal ions in Alloy HR-224 and thus provides better corrosion resistance than as-received samples in SCW environment.