An Investigation into the Corrosion Behaviors of Stainless Steel and Ni-based Alloy in Simulated PWR Primary Water Environments

摘要

Austenitic 316 SS, Alloy 600 and X750 have beenused as structural materials in the pressurized waterreactors (PWRs). With increasing operation times of lightwater reactors, incidents of stress corrosion cracking(SCC) in internal vessels has increased. Componentdegradation might cause SCC to affect the safety ofnuclear plants and would require a huge cost torepair/replace the components.For a better understanding towards SCC inaustenitic stainless steel and Ni-based alloy in simulatedPWR (primary water environments), the SCC initiationbehavior was investigated via U-bend tests in 320°C hightemperaturewater (B: 1200 ppm, Li: 3.5 ppm, DH: 0,0.45 ppm). The experiment duration is up to 1500 hours.Prior to fabricating the U-bend, samples were preparedand underwent various pretreatments, including solutiontreatment (ST) and thermal treatment (TT). After the Ubendtests, morphologies of the surfaces of the sampleswere examined by scanning electron microscopy (SEM).Based on the quantitative analysis of the cracks onthe surfaces of the samples, distinct increases in cracklengths and total crack numbers were observed at thesurface of the thermally sensitized 316 SS. For nickelbased alloys, some pitting corrosion was found on bothAlloy 600 and X750.