Fracture mechanical investigation regarding the effects of crack on the integrity of a BWR-core shroud

Fracture mechanical analyses are carried out for a typical boiling water reactor in connection with crack initiation as a defect detected in core internal components of foreign boiling water reactors as well as the Wuergassen Reactor as a result of intercrystalline stress crack corrosion in order to study the effects of postulated cracks upon the integrity of the core shroud. Critical crack quantities for the operational load case are determined in the framework of these fracture mechanical analyses using a ''lower bound'' fracture toughness K IJ and a crack propagation rate da/dt selected on the basis of its congruency for the reason of observing limits, and the surface crack growth is studied. Previous results for the core welded seams show that crack propagation also comes to a halt approximately in the mid-wall thickness and that, after a slow starting phase, crack propagation runs approximately linearly in the longitudinal direction. This crack propagation behaviour is in agreement with the results of ultrasonic measurements in the H4 core seam range of the Muehleberg reactor core shroud. (orig.)