[en] Since a vessel head penetration had been found leaking at French Bugey 3 plant is 1991, many researches have been performed upon the cracking by PWSCC in CRDM nozzle penetrations. The prediction of both initiation and propagation of nozzle cracks in CRDM must be one of most important issues in the viewpoint of maintenance, safety review and life extension of nuclear power plant. In this study, an improved probabilistic analysis method based on Weibull distribution normalized by key parameters is presented through both vessel inspection data of domestic and foreign nuclear power plants and experimental data of many laboratories, and the applicability to the prediction of crack initiation is evaluated using a specific plant operational condition. The probabilistic approach used in this study might be considered as a realistics method for the prediction of crack initiation in vessel head penetrations with variously different kinds of influencing parameters, though this approach could not make a physically accurate prediction of crack initiation