FRACTURE TOUGHNESS OF IRRADIATED STAINLESS STEEL IN NUCLEAR POWER SYSTEMS

摘要

Data from research programs that measured the fracture toughness of irradiated stainless steels were collected and evaluated by the Electric Power Research Institute (EPRI) to determine the relationship between fracture toughness and neutron fluence for conditions representative of both Boiling Water Reactors (BWRs) and Pressurized Water Reactors (PWRs). Analysis shows that the reduction of fracture toughness with increasing neutron dose in BWRs and PWRs is consistent with that observed in fast reactors. However, a few of these data points at relatively high fluence (between about 2 and 18 dpa) fall below the scatter band for stainless steels irradiated in fast reactors, but no consistent trend between thermal and fast reactors at equivalent doses (expressed in dpa or n/cm2) has been observed. The data indicate that for neutron fluence exposures less than 0.5 dpa, only a limit load evaluation is necessary in order to support continued service. For dose levels up to approximately five dpa, Elastic-Plastic Fracture Mechanics (EPFM) can be considered for design and operational analyses. For higher dose levels, it is recommended that Linear-Elastic Fracture Mechanics (LEFM) analyses be considered. When the neutron exposures are greater than five dpa and less than 15 dpa, LEFM analyses can be used with a limiting fracture toughness (K,J of 55 MPaAm (50 ksNin). At irradiation exposures equal to or greater than 15 dpa, a conservative lower bound fracture toughness of 38 MPa^lm (35 ksvin) is recommended. The results from this study can be used by the nuclear industry to assess the effects of irradiation on the structural integrity of irradiated stainless steels in the presence of flaws in commercial Light Water Reactors (LWRs).