Effect of neutron irradiation embrittlement on cyclic hardening behavior of core shroud assembly in pressurized water reactor under beyond-design basis earthquake

This paper presents investigation results on effect of neutron irradiation embrittlement on cyclic hardening behavior of core shroud assembly in pressurized water reactor under beyond-design basis earthquake (BDBE). In order to simulate the cyclic hardening behavior considering the neutron irradiation embrittlement, the previous user subroutines developed for monotonic hardening behavior were updated based on some cyclic hardening test results of irradiation-simulated specimens. Finite element (FE) elastic-plastic seismic analysis was performed by using Chaboche combined hardening models considering cyclic hardening or cyclic softening and a bi-linear kinematic hardening model. As a result, it is found that the bi-linear kinematic hardening model derived the most conservative results, and the Chaboche combined hardening model considering cyclic softening derived the analysis results close to those of the bi-linear kinematic hardening model. In addition, variation of the FE elastic-plastic seismic analysis results vs. neutron irradiation dose was investigated using the bi-linear kinematic hardening model. Finally, it is identified that von-Mises effective stress and plastic strain energy increase and equivalent plastic strain decreases with increasing the neutron irradiation dose.