Abstract
Hydrogen water chemistry (HWC) was proposed and widely adopted in BWRs worldwide to mitigate the problem of SCC. However, the hydrogen injection can only be applied during normal plant operation due to some limits inherent in the original design. The pressure and temperature gradient during plant start-up could cause the tensile stress conditions. Regarding the water environment, the above factors may contribute to the initiation of SCC. In this study, we compared the SCC behavior between two type of stainless steel with different heat treatments at various temperature in the NWC and HWC during start-up. The SCC behavior and high temperature tensile properties were investigated by performing slow strain rate tensile (SSRT) tests at a constant strain rate of 3.0 × 10-7/s mainly at 200°C, 250°C and 288°C. After SSRT tests, scanning electron microscopy (SEM) was conducted to characterise the fractured surface. Basically, these two materials in the NWC test conditions showed lower SCC susceptibility with the lower testing temperature. Specimens tested under 250oC, however, showed higher tendency toward multiple cracks initiations. On the other hand, the performance of sensitized 316L in the aspects of tensile properties and fractography was substantially improved after introducing the HWC. Nevertheless, the unexpected performances were found on sensitized 304L after injecting hydrogen into the system. The slight differences between materials, heat treatment and water chemistry in the testing conditions were considered as the mian causes of these results.