Session: CS-21-01 Constraint Effects on C&S

Paper Number: 123136

123136 - Biaxial Constraint Effect on Fracture Toughness Evaluation of Reactor Pressure Vessel Under Pressurized Thermal Shock Events 

    According to Japan Electric Association Code (JEAC) 4206, in the structural integrity assessment of the reactor pressure vessel (RPV) during pressurized thermal shock (PTS) events, the fracture toughness curve is evaluated using the fracture toughness data of interested RPV material obtained by fracture toughness test specimens included in surveillance. The stress intensity factor is calculated postulating a crack near the inner surface of RPV. Here, the depth ratio of the postulated crack to the thickness of the RPV (a/t ~ 0.05) is smaller than that for fracture toughness test specimens (a/W ~ 0.5). Such a shallow crack reduces the plastic constraint. Moreover, the crack in actual components is subjected to the biaxial stress due to the thermal shock, and thus the plastic constraint is enhanced. The differences in crack shape and loading condition affect the fracture toughness evaluation. Therefore, it is crucial to investigate the degree of margin in the fracture toughness curve under the shallow crack and biaxial stress conditions.

    To address the above issue, we are planning the multi-axial fracture tests that simulate the stress distribution in the RPV during PTS events. In the paper, the project of the multi-axial fracture test is described. Furthermore, to obtain the reference data for multi-axial fracture tests, fracture toughness tests were performed using standard compact tension (C(T)) specimens, shallow cracked single-edge bending (SE(B)) specimens and flat plate specimens loaded with a uniaxial 4-point bending. The fracture toughness obtained by shallow cracked SE(B) and flat plate specimens was higher than that obtained by those C(T) specimens, and the effect of the low plastic constraint was confirmed. Moreover, the fracture toughness estimation based on the local approach was performed, and the estimated fracture toughness was agreed with the experimentally obtained ones. In the presentation, the fracture toughness of the multi-axial fracture test specimen will be estimated based on the local approach.

Presenting Author: Masaki Shimodaira Japan Atomic Energy Agency

Presenting Author Biography: The presenter is a researcher of Japan Atomic Energy Agency. He was received the Ph.D degrees in engineering from Tohoku University, Japan, in 2018. One of research topics is the fracture mechanics evaluation in terms of the structural integrity assessment for the reactor pressure vessel, mainly using the finite element analysis. Moreover, the irradiation embrittlement mechanism is also investigated using the microstructural analysis techniques, such as transmission electron microscope and atom probe tomography.

Authors:

Masaki Shimodaira Japan Atomic Energy Agency
Yoshihito Yamaguchi Japan Atomic Energy Agency
Keiko Iwata Japan Atomic Energy Agency
Jinya Katsuyama Japan Atomic Energy Agency
Yasuhiro Chimi Japan Atomic Energy Agency