Relationship between Residual Stress of Dissimilar Metal Welding and Stress Corrosion Cracking of Alloy 600 Nozzle in Bottom Mounted Instrumentation of PWR

One of the main concerns of the dissimilar metal weld (DMW) parts in a pressurized water reactor (PWR) is a tensile stress generated by welding or cold working. Under an abnormal welding condition or without a sufficient post-heat treatment, a high tensile stress can be persistent after welding, leading to cracking of the components even in a short-term operation. Under the circumstances, significant efforts have been recently devoted to evaluate the stress generation in the DMW parts during welding and to investigate the effect of the residual stress on the stress corrosion cracking (SCC) of weld metals. However, there is very limited literature on the relationship between the residual stress and the primary water SCC (PWSCC) of the thick wall penetration nozzle of Alloy 600 in the PWR. In this work, the SCC behavior of the bottom mounted instrumentation (BMI) mockup and its dependence on the residual stress of welding are investigated by a finite element analysis (FEA) and an SCC acceleration test in an acidic solution to understand the field experience of PWSCC, especially, of the Alloy 600 nozzle in the PWR