For the integrity assessment of reactor pressure vessel (RPV) under pressurized thermal shock (PTS) condition is the most important event. The integrity of RPV is assessed by comparing stress intensity factor on a crack tip and the fracture toughness obtained from surveillance tests. The miniature compact tension (CT) specimen machined from surveillance specimens is expected to directly evaluate the fracture toughness. However, it has been recognized that a constraint effect in CT specimens is greater than that of the postulated crack in RPV, and it causes a conservative evaluation. Therefore, clarification of the conservativeness is required for more reasonable evaluation. In order to examine the mechanical factors related to the constraint effect of the crack, T stress, Q factor, and Weibull stress are useful. In this study, 3D elastic plastic finite element analyses were performed for CT specimens with different size and RPV models, to evaluate the above mechanical factors. From the analysis results, a larger constraint effect for CT specimens is observed than that for the postulated crack for RPV. We discussed on the conservativeness of the current structural integrity assessment methodology.
