Document: NRC Regulatory Guide
Document ID: 9a8db182-3194-4663-aeb3-64f2e4edd6aa
Document Type: regulatory_guide
Title: Availability of Electric Power Sources (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1008/ML100840581.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.93
CFR Part: 
CFR Title: 

Content:
OURCES A. INTRODUCTION This regulatory guide describes guidelines that the staff of the U.S. Nuclear Regulatory Commission (NRC) considers acceptable when the available electric power sources are less than the number of sources required by the limiting conditions for operation (LCOs) for a facility. This regulatory guide is applicable to single- and multiple-unit plants and is consistent with the improved Standard Technical Specifications (iSTS) (NUREG-1430–1434 (Refs. 1–5)). The LCO-required actions and specified completion times referred to in this regulatory guide are based on the completion times presented in Regulatory Guide 1.93, “Availability of Electric Power Sources,” Revision 0, issued December 1974, which have been incorporated into the required actions in the iSTS. Title 10, Section 50.36(c)(2), of the Code of Federal Regulations (10 CFR 50.36(c)(2)) (Ref. 6), requires that the technical specifications include the LCOs, which are defined as the lowest functional capability or performance levels of equipment required for safe operation of the facility. Furthermore, the same regulations require that, when an LCO of a nuclear reactor is not met, the licensee shall shut down the reactor or follow any remedial action permitted by the technical specifications until the condition can be met. General Design Criterion (GDC) 17, “Electric Power Systems,” of Appendix A, “General Design Criteria for Nuclear Power Plants,” to 10 CFR Part 50, “Domestic Licensing of Production and Utilization Facilities,” (GDC 17) requires, in part, the following: • Two physically independent circuits shall supply electric power from the offsite transmission network to the onsite electric distribution system. Each of these circuits shall be designed to be available in sufficient time following a loss of all onsite alternating current (ac) power supplies and the other offsite electric power circuits. One of these circuits shall be designed to be available within a