FEA Welding Residual Stress and Fracture Mechanics Model for Nozzles With J-Groove Attachment Welds: Methodology and Application

Residual stresses due to welding in reactor pressure vessel (RPV) top head nozzle penetrations have been predicted using finite element analysis since the early 1990s. While the analyses were originally targeted at calculating nozzle stresses, the finite element methods have been extended to model a number of different aspects of RPV head penetrations. Both top and bottom head penetrations have been modeled, and the effects of J-groove butter weld deposition and subsequent thermal stress relief of the top head are now included in the analytical model. Development work has recently been completed to integrate a fracture mechanics model into the welding residual stress model. This has allowed for the prediction of crack tip stress intensity factors in the presence of welding residual stresses that include the effects of stress redistribution due to the presence of the crack. This paper presents some of the modeling techniques used in these recent analyses, and some key results obtained.