Reasons and Measures to Eliminate Operating-Basis Earthquake in Advanced Light Water Reactor Nuclear Power Plant

The requirement to eliminate operating-basis earthquake (OBE) for nuclear power plant seismic design is put forward in advanced light water reactor (ALWR) utility requirement documents (URD), whose position is that it’s unnecessary to perform two complete sets of seismic analyses: one for the OBE and one for the safe-shutdown earthquake (SSE). Relevant Nuclear Regulatory Commission (NRC) departments also discussed the question of how to decouple OBE from SSE. They proposed OBE shouldn’t control the design of safety-related systems, and corresponding memorandums, which were approved by NRC in 1993, were complied according to past research and experience of seismic design of nuclear power plants. This paper deals with two problems according to the memorandums. One is the background and reasons to eliminate OBE, and the other is measures and methods adopted after elimination of OBE, both of which are discussed from seismic requirements of such aspects as structures, pipes, supports, equipments, and decision making after the earthquake.