Effects of geometry of reactor pressure vessel upper head control rod drive mechanism penetration nozzles on J-Groove weld residual stress

In pressurized water reactors (PWRs), the reactor pressure vessel (RPV) upper head contains numerous control re drive mechanism (CRDM) nozzles. In the last 10 years, the incidences of cracking in alloy 600 CRDM nozzles and the associated welds has increased significantly. Several axial and circumferential cracks have been found in CRDM nozzles European PWRs and U.S. nuclear power plants. These cracks are caused by primary water stress corrosion crackir (PWSCC) and have been shown to be driven by welding residual stresses and operational stresses in the weld regio Therefore, detailed finite-element (FE) simulations for the Korea Nuclear Reactor Pressure Vessel have been conducted order to predict the magnitudes of the weld residual stresses in the tube materials. In particular, die weld residual stress resul are compared in terms for nozzle location, geometry factor r₀/t, geometry of fillet, and adjacent nozzle.