The U.S. Nuclear Regulatory Commission perspective on seismic re-evaluation of nuclear power plants: the IPEEE methodology

Since the late 1970 , seismic re-evaluation has been carried out in several stages at the U.S. Nuclear Regulatory Commission (US NRC). In the late 1970 and early 1980 , the Systematic Evaluation Program (SEP) was carried out to re-evaluate the eleven oldest nuclear power plants which received their construction permits between 1956 and 1967. In 1980, I and E Bulletin No. 80-11, was published requesting that licensees evaluate masonry walls whose failure could affect safety-related systems. In the late 1980 , Unresolved Safety Issue (USI) A-46 was initiated to verify the seismic adequacy of mechanical and electrical equipment in many of the older plants. Affected plants were typically those whose construction permit application was docketed (submitted) before about 1972. In the early 1990 the US NRC initiated the Individual Plant Examination of External Events (IPEEE) Program; seismic was one of the major external events that had to be included in the licensee evaluation. This paper focuses on the seismic portion of the IPEEE analyses. It discusses acceptable methods for performing the seismic evaluation, enhancements to these methods that reflected the state-of-the-art improvements (circa late 1980's - early 1990's). Note: Guidance reflecting the current (circa 2000) state-of-knowledge for performing a seismic PRA or seismic margins assessment can be found in ANS, 2000. The NRC has not developed a position on this document. (authors)