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 whichmaterials exposed to neutron irradiation become moresusceptible to SCC with increasing fluence. This is anactive degradation mechanism for stainless steels (SSs) inreactor cores. While proton irradiation has been used toemulate reactor core conditions at a fraction of the timeand cost, with reduced activity, it’s been limited inapplicability partly due to a shallow penetration depth.Canadian Nuclear Laboratories (CNL) has developedsensitive crack initiation testing capabilities forspecimens utilizing actively loaded, blunt-notch tensilespecimens and in-situ crack detection via direct currentpotential drop (DCPD). The goal is to extend the utility ofproton irradiation by employing sensitive DCPDmeasurements and small volume techniques such asnanoindentation. To this end, Grade 304L SS wasirradiated with 2MeV protons using irradiationtemperatures of 360±10oC and 100±20oC to emulateneutron irradiation damage in a sink dominated/voidswelling regime for two cases: SS in the core of a boilingwater 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 nanoindentationstudies to examine changes in material properties, whichsupport investigations of SCC susceptibility. Thecharacteristic depth for the indentation size effect and theincrease in the yield strength from irradiation induceddefects were determined. Furthermore, the irradiationdamage was characterized, as a function of depth, fromthe base of a machined notch and from a polishedsurface. The paper will discuss the spatial distribution ofdefect accumulation around a blunt flaw in the context ofthe mechanistic understanding of IASCC.