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:
ations require the operability of the offsite power system as a part of the LCOs and specify actions to be taken when the offsite power system is inoperable. Plant operators should be aware of (1) the capability of the offsite power system to supply power during operation and (2) situations that can result in a loss of offsite power or inadequate voltage following a trip of the plant or other transmission contingencies (which could potentially degrade the offsite power supplies) identified by the grid operator. If the offsite power system cannot provide the requisite power in either situation, the licensee should declare the system inoperable and follow pertinent plant technical specification provisions. The transmission network (grid) is the source of power to the offsite power system. Accordingly, licensees should perform grid reliability evaluations as part of the maintenance risk assessment required by 10 CFR 50.65, “Requirements for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants” (Ref. 8) (the Maintenance Rule) before performing “grid-risk-sensitive” maintenance activities. If the grid reliability evaluation indicates that degraded grid reliability conditions may exist during maintenance activities, the licensees should consider rescheduling any grid-risk-sensitive maintenance activities. If there is some overriding need to perform grid-risk-sensitive activities under existing or imminent conditions of degraded grid reliability, the licensee should consider alternate equipment protection measures and compensatory actions to manage or minimize the risk. A licensee’s ability to comply with technical specifications for offsite power may depend on grid conditions and plant status. In particular, maintenance on, and the degraded conditions of, the key elements of the plant switchyard and offsite power grid can affect the operability of the offsite power system, especially during times of high grid load and high grid stress. A