Corrosion Behavior Of Candidate Fuel Cladding Materials For Supercritical Water-cooled Reactor

Supercritical water-cooled reactor(SCWR) was proposed as one of the most promising Generation Ⅳ nuclear fission reactor prototypes for large scale electric power plants due to its relatively simplified design, compact layout, and high thermal efficiency, comparing with the current state-of-the-art light water reactors(LWRs). However, above the thermodynamic critical point, SCW coolant is more corrosive and places great challenges to the selection of in-core structure materials, especially the nuclear fuel cladding material. Evaluation of several candidate materials for the SCWR has been conducted on the major fire tube materials used in supercritical fossil fired plants,structural materials used in current nuclear reactors and materials for aero engine blades. For the application of a structural material to a fuel cladding in the SCWR, the material should be evaluated in terms of its corrosion and stress corrosion cracking susceptibility in SCW environment.General corrosion behavior of ferritic/martenstic(F/M) steels(P92 and T91), austenitic stainless steels(HR3C and 304NG), Ni-base alloy(C276) and ODS steels(316-ODS and 310-ODS) were investigated in SCW. The experimental results show that F/M steels exhibit poor general corrosion resistance and exfoliations were observed on the specimens; austenitic stainless steel HR3 C shows excellent general corrosion resistance because of high Cr concentration while sever nodular corrosion appears on 304 NG steel; Ni-base alloy C276 exhibits great general corrosion resistance and the weight gain decrease when the temperature rise from 600℃ to 650℃; austenitic ODS steels also show excellent general corrosion resistance: the oxide scale of 310-ODS is complete and compact while heterogeneous oxide scales were observed on 316-ODS due to the defects of metallurgy process.Slow stress rate tensile(SSRT) tests were accepted in this work to evaluate the stress corrosion cracking(SCC) susceptibility of P92 steel, 316 Ti steel, HR3 C steel, C276 alloy and 310-ODS steel in SCW. Among these five candidate materials, P92 has acceptable mechanical properties and its susceptibility to SCC is very low; 316 Ti steel exhibits terrible mechanical properties and severe transgranular SCC(TGSCC) was observed; HR3 C steel, C276 alloy and 310-ODS steel show excellent mechanical properties, and intergranular SCC(IGSCC) was observed on all these materials, while SCC susceptibility of HR3 C steel and 310-ODS steel is very low and susceptibility to SCC of C276 is very serious.According to the results of screening tests, HR3 C steel and 310-ODS steel have high priority to be selected as fuel cladding materials of SCWR because of excellent general corrosion resistance, high mechanical strength and low SCC susceptibility in SCW.