When the structural integrity of reactor pressure vessel (RPV) under pressurized thermal shock (PTS) events is assessed, an underclad crack is postulated at the inner surface of RPV and the stress intensity factor (SIF) corresponding to the driving force of non-ductile crack propagation, is evaluated for this crack. On the inner surface of RPV, cladding of the stainless steel is overlay-welded as a means for corrosion protection. Because the cladding is a ductile material, it is important to evaluate the SIF for postulated underclad crack considering the plasticity of cladding. A SIF evaluation method, which takes the effect of plasticity into account using a plastic correction method, has been established in France. In this study, we examined the SIF evaluation method established in France for underclad cracks during PTS transients. The elastic and elastic-plastic analyses based on the finite element method considering PTS events and inner pressure were performed using three-dimensional models including an underclad semi-elliptical crack with different geometry. We discussed the conservativeness of plastic correction method based on the analysis results.

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