Seismic Criteria and Practice - Recent Developments in the United States

Abstract

The title of the paper is obviously overly ambitious. Although a thorough research of the available sources of information would help to reasonably define the state of affairs regarding seismic criteria and practice in the U.S., such an attempt requires considerable time and dedication. The objective herein is much more modest and no claim is made for completeness. It simply reflects the author's knowledge of most of the activities that are presently ongoing to resolve several important issues, both old and new, nuclear with respect to the seismic design of facilities. References are given to all source documents and liberal transcriptions (without quotation) of cogent statements are made to minimize the chance of modifying their original intent. Despite the fact that for almost a decade now no new nuclear power plants have been ordered in the U.S., and that during the same period a host of cancellations and postponements have also plagued the industry, interest is seismic design considerations has not abated in the United States. Although it would be useful to speculate on this trend, the paper emphasizes the major developments in recent years as advanced in practice, research and regulations. All aspects of seismic design, from the definition of ground motion to the qualification of equipment and components, from deterministic design procedures to probabilistic evaluation of the safety of nuclear power plants, have been undergoing change and development over the last several years. These developments are reviewed under the main objectives of safety/regulations, design improvements and standardization. A review of the Division K papers of the 7th SMiRT (Structural Mechanics in Reactor Technology) Conference, held in Chicago, August 22-29, 1983, shows that the U.S. contribution is a healthy 38% of the total (Western Europe contributed 38%; Japan 17%; and the remaining 7% by others}. The more interesting outcome of this survey was that 41% of the U.S. contributions came from small consulting firms in contrast to only 15% by Architect/Engineers and NSSS Suppliers, who used to dominate earlier conferences, National Laboratories and Universities contributed 22% each. The work of the small consulting firms is supported by the National Laboratories and power utility companies. The statistics clearly indicate that the present work in the U.S. is geared mainly towards the re-evaluation of the older plants and/or verification of design and analysis concepts used for plants presently under review.