Development of a Performance-Based Approach to Seismic Siting and Design

摘要

In 1996 and 1997, the U.S. Nuclear Regulatory Commission (NRC) published a new Title 10, Section 100.23, "Geologic and Seismic Siting Criteria," of the Code of Federal Regulations (10 CFR 100.23) and a series of supporting regulatory guides. Regulatory Guide 1.165, "Identification and Characterization of Seismic Sources and Determination of Safe Shutdown Earthquake Ground Motion," issued March 1997 [1], is one of this series and contains the basic guidance for the development of the safe-shutdown earthquake (SSE) ground motion response spectra (GMRS), which is the characterization of seismic loading that governs the seismic design of nuclear power plants (NPPs). This guidance was effectively untested until three utilities applied for early site permits in 2003. In the same timeframe, the Electric Power Research Institute (EPRI) completed a comprehensive new study of the attenuation of seismic ground motion for the central and eastern United States [2]. Using this updated ground motion attenuation model in the EPRI probabilistic seismic hazard assessment (PSHA) methodology, in a number of cases, site-specific GMRS exceed the seismic response spectra used in the certification of new NPP designs. These exceedances are in the high-frequency portion of the response spectra and might or might not represent challenges to the facility.To address the issue of these exceedances, the Nuclear Energy Institute (NEI), acting for the U.S. nuclear industry, proposed a revision of the regulatory guidance based on a risk-informed, performance-based approach described in the American Society of Civil Engineers (ASCE) and Structural Engineering Institute (SEI) standard ASCE/SEI 43-05, "Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities" [3], finalized in July 2005. In addition to proposing to change the basis of the regulatory guide to a risk-consistent approach, NEI has proposed several changes to the PSHA methodology. This paper describes the risk-informed, performance-based approach and technical basis of the ASCE/SEI 43-05 standard, associated regulatory issues, and details of proposed changes to the PSHA methodology. Based in part on ASCE/SEI 43-05, the NRC staff published a draft of a new regulatory guide for public comment in December 2006 and issued the final version, Regulatory Guide 1.208, "A Performance-Based Approach to Define the Site-Specific Earthquake Ground Motion" [4], in March 2007.