Assessing the impact of irradiation-induced defects on the hardening of reactor pressure vessel materials for sustainable development of nuclear energy

Abstract

The operational longevity of a nuclear power plant, specifically of the light water reactor type, hinges on the assessment of component degradation, with a particular focus on the reactor pressure vessel (RPV) materials. Among the most prevalent defects responsible for irradiation-induced hardening in RPV materials are point defects (PDs) and dislocation loops (DLs). However, their respective contributions to the overall hardening of RPV materials have not been clearly determined. To address this issue, this study was conducted using iron alloys with equivalent Mn and Ni content to those used in nuclear RPV in Japan. The study employed transmission electron microscopy (TEM), atom probe tomography (APT), and nanoindentation to assess the roles of PDs and DLs in contributing to the hardening behaviour of RPV materials. The results indicated that both solute clusters (SCs), which are formed by the aggregation of PDs, and DLs play equally important roles in the hardening behaviour of RPV materials. However, an in-depth analysis of three-dimensional images using the APT method revealed that there may have been errors in evaluating SCs and DLs, leading to double counting when assessing the impact of irradiation-induced defects on the hardening behaviour of RPV materials. These findings highlight the need for improved accuracy in evaluating these defects to better understand the behaviour of RPV materials under irradiation.