Residual stress improvement by water jet peening for bottom mounted instrumentation (BMI) nozzle - abs11

BMI nozzle, which is on bottom of reactor vessel and a part of pressure boundary of the primary system of PWR plants, has residual tensile stress produced by welding on internal surface, and the stress might occur Stress Corrosion Cracking; SCC. From the point of view of safe operation, it is important to improve the stress on BMI nozzle. MHI has developed an effective stress improvement method for inner surface of BMI nozzle with cavitation impact generated by water jet, called Water Jet Peening; WJP. WJP is effective if there is no flaw which extends more than 0.5 mm depth on surface, so eddy current test (ET), is performed before WJP to confirm that there is no flaw deeper than 0.5 mm on BMI surface. The stress improvement method for inner surface of BMI nozzle with ET and WJP has already been applied to 2 plants in Japan. (authors)