Abstract: The thermo-elastic-plastic finite element simulations are conducted to investigate the distributions of the weld residual stresses in the J-weld for a center-hole control rod drive mechanism (CRDM) nozzle and the full residual stress solution from the weld analysis is mapped directly to the three-dimensional finite element model with a crack, then the equivalent Keq-solution along crack front is extracted after application of the operating pressure and temperature. The results from these analyses show that the hoop residual stresses are much higher than the axial residual stresses in the CRDM nozzle. The peak stress intensity factor always appears in the front of the crack near the J-weld zone rather than at the center of the crack because of the high tensile weld residual stress in the J-weld. The increase of the stress intensity factor Keq caused by the increase of crack depth ratio a/δ is much higher than that caused by the increase of crack length 2c. The crack in the CRDM nozzle near the J-weld zone will grow in a nature shape which is controlled by the actual distribution of the stress intensity factor along the front of the crack, and does not grow in the semi-elliptical shape which is assumed by the present codes. For conducting the accurate crack growth analysis and safety assessment, the detailed finite element analyses are required to determine the weld residual stress fields and the stress intensity factor Keq values along the front of the cracks.

Key words: Axial cracks, Control rod drive mechanism, Finite element, J-weld, Stress intensity factor, Weld residual stress