Session: CS-10-01 Recent Developments in Japanese Codes and Standards

Paper Number: 61892

Start Time: Tuesday, July 13, 2021, 05:00 PM

61892 - Fracture Toughness in Postulated Crack Area of PTS Evaluation in Highly-Neutron Irradiated RPV Steel 

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.

Presenting Author: Yoosung Ha Japan Atomic Energy Agency

Authors:

Yoosung Ha Japan Atomic Energy Agency
Masaki Shimodaira Japan Atomic Energy Agency
Hisashi Takamizawa Japan Atomic Energy Agency
Tohru Tobita Japan Atomic Energy Agency (JAEA)
Jinya Katsuyama Japan Atomic Energy Agency
Yutaka Nishiyama Japan Atomic Energy Agency