NANO-MECHANICAL TESTING OF PROTON IRRADIATED 304L SS AT 100°C AND 360°C TO SUPPORT IASCC

摘要

Irradiation-assisted stress corrosion cracking (IASCC) is a complex failure mechanism for which materials exposed to neutron irradiation become more susceptible to SCC with increasing fluence. This is an active degradation mechanism for stainless steels (SSs) in reactor cores. While proton irradiation has been used to emulate reactor core conditions at a fraction of the time and cost, with reduced activity, it's been limited in applicability partly due to a shallow penetration depth. Canadian Nuclear Laboratories (CNL) has developed sensitive crack initiation testing capabilities for specimens utilizing actively loaded, blunt-notch tensile specimens and in-situ crack detection via direct current potential drop (DCPD). The goal is to extend the utility of proton irradiation by employing sensitive DCPD measurements and small volume techniques such as nanoindentation. To this end. Grade 304L SS was irradiated with 2MeV protons using irradiation temperatures of 360±10°C and 100±20°C to emulate neutron irradiation damage in a sink dominated/void swelling regime for two cases: SS in the core of a boiling water reactor or pressurized water reactor (288-330°C) and SS at the periphery of a CANDU reactor core (60-80°C). Post-irradiation testing involved nanoindentation studies to examine changes in material properties, which support investigations of SCC susceptibility. The characteristic depth for the indentation size effect and the increase in the yield strength from irradiation induced defects were determined. Furthermore, the irradiation damage was characterized, as a function of depth, from the base of a machined notch and from a polished surface. The paper will discuss the spatial distribution of defect accumulation around a blunt flaw in the context of the mechanistic understanding of IASCC.