A probabilistic approach to predict crack propagation in steam generator tubes

Steam generator pipe rupture is an accident that affects the availability and safety of nuclear plants. In order to reduce the possibility of this event, utilities developed a maintenance plan to inspect the tubes by eddy-current test at each plant outage. Tubes are plugged when crack length is greater than limits previously established using deterministic procedure. Available data worldwide indicate that stress corrosion crack is the controlled mechanism to cracks initiation and propagation. Because the same trend has been observed in Angra 1, a strategy to manage the problem is necessary to extend the steam generator lifetime. The first results of this investigation, related to structural area, are presented in this paper. The approach is based on probabilistic fracture mechanics and the purposes of the study are: to identify the key variables and their statistical distribution; to define the new plugging limit at which tube repair is necessary without challenger the safety. (author)