A bottom mounted instrument (BMI) nozzle in a European nuclear pressure vessel experienced some cracking caused by primary water stress corrosion cracking (PWSCC). Rather than repair the nozzle a decision was made to place a plug over the nozzle hole since this particular instrument panel could be removed in the reactor. The plug repair will be installed remotely during an outage and consists of performing the welding from a location near the top of the vessel which is more than 20 meters away. This makes the design of the repair critical.
This paper uses 3D computational weld analyses to design the repair. Considerations for the design include the possibility of repair welds, proper seating of the plug (distortion control), weld residual stress control, and load applications to the plug during the repair process. Computational weld modeling permitted a proper design to be realized and helped in the regulatory certification process for the plug repair. These are discussed in this paper.
