General Corrosion And Susceptibility To Stress Corrosion Cracking Of Candidate Cladding Materials For Supercritical Water Cooled Reactors

The supercritical water cooled reactor (SCWR) is a promising conceptfor the future development of world nuclear energy technology due to itshigher thermal efficiency, higher utilization of nuclear fuels and simplerstructures as compare to current light water reactors (LWR). However,SCWRs require fuel cladding materials to have good mechanicalperformance, excellent corrosion resistance and less susceptibility to stresscorrosion cracking (SCC). The cladding materials currently used for LWRs,such as zircaloys, can not satisfy this requirement because of their lowstrength and high oxidation rate at the high temperature and pressure of aSCWR. Based on the present knowledge, the research and development ofSCWR cladding materials are mainly focused on austenitic stainless steels,nickel based alloys and ferritic/martensitic (F/M) steels.General corrosion behaviors of austenitic stainless steel TP347HFG, nickel based alloys825and F/M steels12Cr were investigated in circulatingsupercritical water at temperature of650°C, pressure of25MPa. The resultsshowed that the corrosion rate evaluated by weight gain of F/M steels ismuch higher than that of austenitic stainless steels TP347HFG and nickelbased alloys825. Also, TP347HFG and12Cr F/M steel showed severeoxidation at the beginning and exfoliation of oxide films after exposed insupercritical water for1200h and600h, respectively. Alloy825exhibits thelowest weight gain rate among the materials tested, which is less than50mg/dm~2.Slow strain rate tensile (SSRT) tests were used to study stress corrosionbehaviors of candidate fuel cladding materials for SCWRs. Austeniticstainless steel HR3C, nickel based alloys825and800H, and F/M steel12Cr3WVTa were tested in supercritical water at temperature of550,600,650°C, pressure of25MPa, and at strain rate of1×10-6s-1. The results showedthat HR3C, alloy825and800H which have high concentration of Cr and Niexhibit better mechanical performance than12Cr3WVTa which have lowconcentration of Cr and Ni. But these three materials have tensile strengthlower than300MPa at650°C, and alloy825has higher tensile strength andelongation than the others. HR3C and12Cr3WVTa have both ductile fractureand intergranular cracking at550°C, which indicates the susceptibility to SCC. HR3C and800H showed only ductile fracture at650°C and600°C,thus having the least susceptibility to SCC.