Seismic Qualification by Testing for Electrical and Active Mechanical Equipment to be Installed in Hard-Rock High Frequency Sites

Abstract

All electric and active mechanical equipment important to safety must be seismically qualified by either analysis, testing, or a combination of both. The general requirements for seismic qualification of electric and active mechanical equipment in nuclear power plants are delineated in Appendix S to Title 10, Part 50, of the Code of Federal Regulations (10 CFR Part 50), item 52.47(20) of 10 CFR 52.47, and Appendix A to 10 CFR Part 100. The staff at the US Nuclear Regulatory Commission (NRC) has recognized that the Certified Design Ground Motion may be exceeded by the site-specific ground motion. The exceedances are generally in the high-frequency range for the Central and Eastern US sites. For equipment seismic qualification consideration, the exceedances must be addressed at both the ground level and the floor level where the equipment is located. Thus, the in-structure response spectra at some locations may exceed those in-structure response spectra generated by the certified seismic design response spectra. The U.S. nuclear industry and the NRC have initiated activities to address this issue. Two scenarios that revealed themselves during the review activities of the design certification and combined license applications for new reactors will be expounded upon in the paper. In Case I, equipment seismic qualification has been approved for a certified design and equipment is to be installed at a hard-rock high frequency (HRHF) site with certified seismic design response spectra (CSDRS) exceeded by the Ground Motion Response Spectra (GMRS) of the hard-rock site. In Case II, equipment seismic qualification has not been approved for a design certification and there is an application with GMRS exceeding the not-yet-approved CSDRS. In the paper, the staff will begin the discussion with the regulatory requirements for seismic qualification of electric and mechanical equipment. The focus of the paper is to identify the staff concern and illustrate the resolution between the NRC staff and an applicant on the seismic qualification of equipment by testing, in particular for equipment to be installed in hard-rock high frequency sites, to meet the regulatory requirements.