Applicability of Fracture Evaluation Method Based on Local Approach To An Irradiated Low-Alloy Steel

In the structural integrity assessment of the reactor pressure vessels (RPVs), the stress intensity factor acting on the tip of a postulated crack is compared with the fracture toughness evaluated by the fracture toughness test and the Charpy impact test. The plastic constraint of the postulated crack in the RPV is lower than that of the fracture toughness specimen due to the shallow crack depth. Recently, a rational fracture assessment method considering the plastic constraint has been developed for RPVs based on the local approach (LA). To apply the LA for the assessment of RPVs subjected to neutron irradiation, the applicability of the LA for the irradiated low-alloy steel was investigated by confirming the effect of irradiation on Weibull parameters, m and σu. We performed the fracture toughness test and finite element analysis (FEA) for the irradiated low-alloy steel with the reference temperature shift of the fracture toughness of 135°C. The load vs. displacement relationship for the irradiated 0.16T-C(T) specimen was successfully replicated by FEA with the tensile properties after irradiation. The slope of the Weibull plot of σw for irradiated steel could be replicated by using the m value optimized for unirradiated steel, suggesting that the m value was not affected by irradiation. Moreover, it was suggested that the σu value was needed to optimize after irradiation to accurately estimate the KJc distribution, considering the change in the tensile properties after irradiation.