<p>Japanese electric association code (JEAC) 4206 prescribes the structural integrity assessment method of reactor pressure vessel (RPV) considering the irradiation embrittlement and pressurized thermal shock events. In the code, the semi-elliptical crack sized 10 mm in depth x 60 mm in length shall be postulated near the inner surface of an RPV. Because the manufacturing process of RPV affects the microstructural property in plates, the through-thickness distributions of mechanical properties such as hardness, fracture toughness and so on are known to be varied. In addition, the heat-affected zone (HAZ), which is generated at the inner surface under weld-overlay cladding, corresponds to the postulated crack area prescribed in JEAC4206-2016. However, the effect of metallurgical inhomogeneity in HAZ on fracture toughness and irradiation embrittlement has not been clarified yet. In this paper, the mechanical and microstructural properties within HAZ under the cladding were firstly evaluated for comparing with those of base metal. To confirm the metallurgical properties of HAZ, we mapped the phase fractions and morphologies using the scanning electron microscope and finite element analysis. From the results, we clarified that the lower-bainite in coarse-grain HAZ near the interface of cladding and base metal may cause higher hardness and fracture toughness than those of base metal. In irradiated HAZ and base metal, the hardness of HAZ was higher than that of base metal. Additionally, the fracture toughness at 10 mm from the cladding, where corresponds to evaluation point of the structural integrity assessment in JEAC4206-2016, was greater than that of base metal. Since solute cluster is known as one of main factors of the irradiation embrittlement of RPV steels, we performed solute cluster analyses for HAZs under the cladding, including the position of 10 mm from the cladding, and base metal by using atom probe tomography. The cluster chemical composition, volume fraction and so on at selected positions were not significantly different.</p>

Fracture Toughness in Postulated Crack Area of PTS Evaluation in Highly-Neutron Irradiated RPV Steel

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

ASME 2021 Pressure Vessels & Piping Conference (PVP2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.