RELIABILITY OF AN HTR-MODULE PRIMARY CIRCUIT PRESSURE BOUNDARY INFLUENCES, SENSITIVITY, AND COMPARISON WITH A PWR

The reliability of the HTR-module for electricity and steam generation was analysed for normal operation, as well as accident conditions. Th e probabilistic fracture mechanics assessment was performed with a mod ification of the ZERBERUS code on the basis of widely used data. The c alculated failure probabilities may thus be compared with similar inve stigations. The HTR-module primary circuit pressure boundary as a unit showed leak-before-break behaviour in a probabilistic sense, although a break was more probable than a leak for some of its parts. However, the findings may depend greatly on the stochastic data. Therefore a s tochastic reference problem is defined and the results are compared wi th the Japanese round robin on a PWR section. Possible changes of fail ure probabilities and of the leak-before-break behaviour are discussed for different criteria for the events leading to a leak, and for modi fications of the stochastic reference problem such as the inclusion of NDE. The results may be used to identify those stochastic variables w hich have the greatest influence on the computed failure probabilities , and to perhaps justify further work which would provide more detaile d information on these probabilities. Furthermore, there is an obvious need for reduction of the non-statistical reasons for great variation s of failure probabilities.