Study on effects of zinc addition and dissolved hydrogen on oxidation and environmentally-assisted fatigue of 316 stainless steel in PWRs

Abstract

Austenitic stainless steels (ASSs) are commonly used as structural materials in pressurized water reactors (PWRs) due to their excellent corrosion resistance and reasonable mechanical properties. However, a phenomenon known as environmentally-assisted fatigue (EAF) occurs, leading to a significant decrease in fatigue life due to a high-temperature water environment, and cyclic loading caused by thermal stress and mechanical vibration. Evaluating EAF is essential for ensuring the safety and integrity of operating nuclear power plants (NPPs), and fatigue design analysis should be carried out in accordance with the Regulatory Guide issued by the US Nuclear Regulatory Commission. However, EAF life can decrease significantly in some transient sections, which becomes a burden for fatigue analysis. In this thesis, as a part of efforts to improve the EAF behavior of ASSs, the effect of zinc addition into PWR primary water chemistry and optimization of dissolved hydrogen, known to affect primary water stress corrosion cracking (PWSCC) susceptibility, on corrosion and EAF behavior was investigated. In addition, by simulating the oxidation behavior at the fatigue crack tip region, an EAF mechanism was proposed by revealing the relationship between the characteristics of the crack tip oxide film and the EAF life.