The Japanese Electric Association Code 4206-2016 requires that the semi-elliptical crack sized 10 mm in depth × 60 mm in length shall be postulated near the inner surface of a reactor pressure vessel (RPV) in pressurized thermal shock events. The fracture toughness distribution was investigated in the postulated crack area under the PTS events of unirradiated and highly-neutron irradiated RPV steels. Vickers hardness in heat-affected zone (HAZ) due to stainless overlay cladding and 10 mm from the cladding were higher than that of a quarter thickness position, where the surveillance specimens are machined, for both unirradiated (E1) and irradiated (up to 1 × 1020 n/cm2, WIM) materials. Fracture toughness of HAZ and 10 mm from the cladding was higher for the above highly-neutron irradiated material. The same result was obtained in the unirradiated material. Therefore, it was confirmed that fracture toughness obtained from surveillance specimens can provide conservative assessment of structural integrity of RPV.

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