Document: NRC Regulatory Guide
Document ID: cdc706d5-60ed-40a4-b55a-9771904107a7
Document Type: regulatory_guide
Title: Seismic Qualification of Electric and Mechanical Equipment for Nuclear Power Plants (Rev. 4)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1809/ML18093A675.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.100
CFR Part: 
CFR Title: 

Content:
of Mechanical and Electrical Equipment in Operating Nuclear Power Plants.” In 1980, the NRC staff raised a safety concern that licensees had not conducted the seismic qualification of electrical and mechanical equipment in some plants with construction permit applications docketed before about 1972 in a manner that would comply with the licensing criteria that the staff had adopted by 1980 (i.e., RG 1.100, Revision 1, issued August 1977 (Ref. 11), which endorses IEEE Std 344-1975 (Ref. 12)). Therefore, equipment in the older NPPs might not have been adequately qualified to ensure its structural integrity or proper functionality in the event of an SSE ground motion. As a result, the NRC established the USI A-46 program in December 1980 and, in February 1987, issued DG-1328, Page 5 Generic Letter (GL) 87-02, “Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors, Unresolved Safety Issue (USI) A-46” (Ref. 13), to address this safety concern. The NRC staff categorized approximately 70 NPP units in the United States as “USI A-46 plants.” In 1982, the Seismic Qualification Utility Group (SQUG) developed a database using earthquake experience and test experience to address USI A-46. Because of the scarcity of data on equipment in U.S. NPPs subjected to strong earthquake motion, the SQUG and its contractors performed a pilot study to determine the feasibility of using actual earthquake experience data from nonnuclear plants located worldwide (e.g., fossil-fueled power plants, substations, and petrochemical plants) and existing test experience data from U.S. NPPs to evaluate the performance of electrical and mechanical equipment in those facilities to infer the susceptibility of similar NPP equipment to seismic loads. The SQUG concluded, and the NRC agreed, that the use of experience data was feasible to verify the seismic adequacy of equipment in the older USI A-46 plants. The staff does not accept the use of SQUG guidelines