Frequencies of leaks and breaks in safety related piping of PWR-plants as initiating events for LOCAs

The analysis of the effects of LOCA events shows, that there are various ranges of leak rates that are to be distinguished corresponding to the capabilities of systems that are directed to assure the safe condition of the plant. The actuation and subsequent operation of these systems is a further barrier to prevent core damage. Other ranges apply for the steam generators. The frequency of some leak rates will be dominated by inadvertent or faulty opening actions of valves. Some LOCA-relevant leak rates however are mainly caused by wall-penetrating cracks or a break of a pipe. These damages in the walls of the primary coolant retaining system and their frequencies will be discussed here. (orig.)