Probabilistic prediction of crack depth distributions observed in structures subjected to thermal fatigue

Asayama, Tai ; Takasho, Hideki*; Kato, Takehiko*

The application of risk-based technologies is the way to be pursued for the improvement of design of new reactors such as fast breeder reactors. When doing so it is necessary to develop an analytical method that is capable of estimating failure probabilities without a large failure database that requires operational experiences. The prediction method should estimate failure probabilities based on actual mechanisms that cause failure. For this purpose, this study developed a probabilistic structural reliability evaluation method for fatigue. This method is capable of modeling crack initiation, crack propagation, as well as crack depth density distribution at a given cycle. To verify the methodology, crack depth distribution observed in thermal fatigue test specimens were evaluated, and it was shown that the method could reproduce the observed crack depth distributions fairly well. Further improvement will allow this methodology to be applied to the procedure of optimization of inservice inspection planning, as well as to the optimization of safety factors in component design of nuclear plants.