Assessment of the reliability of primary components of a pressurized water reactor by probabilistic fracture mechanics

The reliability of structural components estimated by probabilistic fracture mechanics is governed by three parameters: the loads, the material properties and the number and size of defects in the structure. It is calculated by the well-known convolution-integral assuming all input variables as distributed values. This integral is evaluated by using the Monte Carlo technique with importance-sampling. Two failure modes of two different primary components of a PWR are considered: brittle fracture of the reactor pressure vessel; leakage of the main coolant pipe. The most important parameter will be the defect distribution. There are considered several ways of coming up with such a distribution. Additionally different actions are taken into account, e.g. pre-service and in-service ultrasonic inspections and/or hydro-tests. Taking into account the short intervals between the in-service inspections (e.g. four years) the reliability of the components referred to can be shown to be extremely high. (author)