Microstructural aspect of irradiation assisted stress corrosion cracking of LWR in-core structural materials

Microstructural evolution of proton-irradiated austenitic stainless steels and Inconel 600 alloy were studied in the temperature range interesting to light water reactor (LWR) core conditions. Radiation-induced solute segregation was observed in all irradiation temperatures at dose of 0.1 dpa and above. Constant extension rate test (CERT) was performed to study the irradiation-assisted stress corrosion cracking (IASCC) behavior of these alloys. Void swelling, dislocation and loop structures, and phase transformation were studied to understand the relationship of microstructural evolution to the IASCC phenomenon. It is found that in low carbon austenitic stainless steels, the gamma --> alpha phase transformation could play an important role in stress corrosion cracking mechanism. Twining dislocations were observed in 304L specimens irradiated at 230 degreesC to 1 dpa.