Prediction of radiation hardening in reactor pressure vessel steel based on a theoretical model

A theoretical model is presented that calculates the amount of hardening in reactor pressure vessel (RPV) steels under neutron irradiation. A reaction rate theory is used to describe the evolution of radiation-induced microstructures. The point defect clusters (PDC) and copper-rich precipitates (CRP) have been recognized as contributing to radiation hardening in irradiated alloys, which act as barriers to the dislocation motion on the slip plane. The model includes a detailed description of PDC and CRP, and estimates the increase in yield strength due to these microstructures. The yield strength changes predicted by the model calculation are compared with the measured yield strengths, which were obtained from a surveillance program in French pressurized water reactors (PWR) and from post-irradiation tests performed at a high-flux advanced neutron application reactor (HANARO) in Korea. A fair agreement was found between estimated and observed hardening of irradiated RPV steels in spite of uncertainty about a broad range of irradiation and material parameters. The calculation results imply that the inclusion of CRP tends to overestimate the amount of radiation hardening in low-copper RPV steels. Therefore, the PDC evolution is more important for predicting the amount of radiation hardening in low-copper steels.