HTGR Knowledge Base

Conference Article: Seismic analysis of the modular high temperature gas cooled reactor

Tajirian, F.F.; Longstreth, M.; Appleford, A. (Bechtel National, Inc., San Francisco, CA (USA))

Abstract

This paper reviews the seismic analysis performed for the modular high-temperature gas cooled reactor (MHTGR). The four unit MHTGR nuclear island consists of four separate underground concrete silo structures embedded to a depth of 160 feet. The major NSSS components, including the reactor vessel, and steam generator are housed in the silos. A three-dimensional (3-D) soil-structure interaction (SSI) analysis was performed using the computer program SASSI to develop the seismic loads, acceleration time histories, and response spectra which are to be used in determining the seismic capabilities of the reactor building and its ''safety-related''internal systems and components. The analysed 3-D model included the below grade structures, the reactor and steam generator vessels, the reactor core and other internal structures. A 3-D analysis was performed to take full advantage of embedment in reducing seismic response. The computer program SASSI was selected because it can model 3-D multiple embedded flexible foundations with arbitrary shapes. In the MHTGR design, it is important to model the silo flexibility. The MHTGR is being developed as a standardized plant with a design which envelopes the seismic conditions at 85 percent of U.S. nuclear sites. The maximum Safe Shutdown Earthquake (SSE) acceleration is 0.3g. The paper will review the following subjects: Seismic criteria, and site conditions. Method of analysis. Silo and NSSS models used. Results of the analysis including maximum accelerations and response spectra in the silo and critical equipment supports. The advantages of embedment have been clearly demonstrated in this analysis and will be reviewed in the conclusions of this paper. Furthermore, the results of a separate analysis to assess the effects of silo-soil-silo interaction effects will be discussed.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Seismic behaviour of gas cooled reactor components. Proceedings of a specialists' meeting held in Gif-sur-Yvette, France, 14-16 November 1989
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--22, pp:78-85