Historic Perspective on Design Basis Accident based on experience in Canada, Russia and the United States: Synthesis

It described the early developments and evolution of design criteria based on experience with the advent of higher power facilities in Canada, the United States and Russia. The design bases have evolved with time in each country, reflecting the lessons learned from operational experience and ongoing research efforts. Credit has been given for leak before break analyses to some extent in each country, primarily to permit removing pipe whip restraints that protect against very fast opening large breaks in the primary circuit. These have been done based on fracture mechanics analyses, and the availability of leakage detection devices. There are several concerns, explored in the detailed papers in this session, as well as the rest of this workshop, that an over-emphasis on an accident initiator with exceedingly low frequency of occurrence may divert from an optimal safety design