Technical Issues on Seismic Design of Nuclear Piping Systems

The design of nuclear piping systems has evolved significantly since the first Section III plants were constructed in the early 70s. Effective design to accommodate seismic loads is the dominant problem in the industry. The Section III code committee has been working since the late 80s to develop new seismic stress limits. Code revisions were incorporated in 1994, but to date, have not been accepted by NRC. Hence, appropriate piping seismic stress limits is one very significant technical issue. A second significant issue is revisions to seismic design requirements in 10CFR50 that NRC has made. It is now acceptable to design only for SSE loads, if the plant is shut down for inspection for a seismic event of equal to or greater than 1/3 the SSE. A third issue is whether the amplified response levels required for modern designs are reasonable and appropriate. The purpose of this paper is to explore these three issues. Recommendations are provided.