IRRADIATION ASSISTED STRESS CORROSION CRACKING (IASCC) OF LOW STRENGTH AND HIGH STRENGTH ALLOYS IN LIGHTWATER REACTOR ENVIRONMENTS

摘要

Irradiation-assisted stress corrosion cracking(IASCC) is one of the primary degradation modes forstructural materials in light water reactors. As reactorsage, the accumulated damage generates new concerns forIASCC susceptibility of core materials. Seven austeniticalloys: 316L SS, 310 SS, 690, and C22 (low strengthalloys), and X750, 718 and 725 (high strength alloys)were irradiated to nominal damage levels of 2.5 and 5dpa, and two ferritic/martensitic (FM) steels: T92 and14YWT were also irradiated to 2.5 dpa. Radiationinduced microstructure including voids, loops andprecipitates were characterized. The IASCC resistancewas evaluated by constant extension rate tensile (CERT)tests to 4% strain in both simulated BWR normal waterchemistry (288°C high purity water, 2000 ppb O2) andPWR primary water (320°C, 1000 ppm B, 2 ppm Li, 35cc/kg H2). Cracking severity was evaluated by cracklength per unit area, as it incorporates both the number ofcracks and their length. Clear degradation in IASCCresistance was observed in these alloys as dose increasedfrom 2.5 to 5 dpa. Despite significant microstructuralchanges, no single microstructural feature was identifiedthat could account for the degradation in IASCCresistance in these alloys. Among these alloys, alloys 690and X750 were identified as the most IASCC resistantmaterials for low strength and high strength application,respectively.