Applicability of fracture evaluation method based on local approach to an irradiated low-alloy steel

Shimodaira, Masaki ; Ha, Yoosung  ; Yamaguchi, Yoshihito ; Hata, Kuniki ; Katsuyama, Jinya  

In the structural integrity assessment of the reactor pressure vessels (RPVs), the stress intensity factor acting on the tip of a postulated crack compares with fracture toughness evaluated by the fracture toughness test. The plastic constraint of the postulated crack is lower than the fracture toughness specimen due to the shallow crack depth. Assessing the structural integrity of the RPV with a low-constraint specimen may give an overly conservative result. Recently, a rational fracture assessment method has been developed for RPVs based on the local approach (LA). The LA can estimate the fracture toughness distribution using the Weibull stress, an index of the fracture independent of the plastic constraint. To apply the LA for RPV, it must be confirmed to accurately estimate the Weibull stress and the fracture toughness distribution. In this study, we focused on Weibull parameters, such as shape parameter m and the scaling factor , which are used to calculate the Weibull stress and the fracture probability, respectively. The effect of neutron irradiation on these parameters was investigated by conducting fracture toughness tests and finite element analyses. As a result, the m value corresponding to the uncertainty of the Weibull stress was not affected by irradiation. In contrast, it was found that the value should be optimized to accurately estimate the fracture toughness distribution for irradiated steel, considering the change in the tensile property.