Effect of zinc injection on mitigating stress corrosion cracking initiation of structural materials in light water reactor primary water

The effect of zinc (Zn) injection on the stress corrosion cracking (SCC) initiation of an Alloy 182 weld metal and a 20% cold-worked (CW) type 316L stainless steel was investigated under simulated light water reactor conditions. Accelerated SCC initiation tests revealed that under both, boiling (BWR) and pressurized water reactor (PWR) conditions without Zn injection, Alloy 182 showed a higher SCC initiation susceptibility compared to the CW 316L stainless steel. With 40 ppb Zn injection, results indicate a tendency towards higher stress thresholds or lower crack densities for SCC initiation in both materials. In other words, Zn water chemistry seems to be able to mitigate SCC initiation. The optimized, Zn-treated oxide film is believed to be responsible for the improved SCC performance. However, no clear mitigation effects were observed when the specimens were pre-exposed to high-temperature water without Zn and then tested with Zn, which is likely related to the relatively short exposure time to the Zn-containing high-temperature water.