抄録
It is very important to grasp failure probability and a failure mode appropriately to carry out risk reduction measures of the nuclear power plants. To clarify the important factors for the failure probability and failure mode of the pipe subjected to the temperature change, failure probability analyses changing the values of a stress range, stress ratio, stress components, a threshold stress intensity factor range were performed. The important factors for the failure probability are temperature fluctuation range, stress ratio (mean stress condition) and effective threshold stress intensity factor range. The important factor for the failure mode is temperature fluctuation circumferential angle. When a large temperature fluctuation acts on fully circumferential surface of the pipe, the probability of pipe break increases, and measures to prevent such a failure and to reduce a plant risk are demanded. When the circumferential angle subjected to a temperature change is small, the failure mode is the leak and the corrective maintenance might be applicable at the point of view of the plant risk.
