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:
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 communication protocol with the plant’s TSO combined with an understanding of the TSO capabilities can help the NPP operator understand changes in the grid that can affect plant operations. The capability and reliability of the power grid is important to the licensee and can be used to determine the effects of these changes on the operability of the plant’s offsite electrical power system. Data collected in response to GL 2006-02 (Ref. 7) determined that the majority of TSOs serving NPP sites have analysis tools which give the TSO the capabilities to determine the impact of the loss or unavailability of various transmission system elements, or contingencies, on the condition of the grid. The transmission systems can generally cope with several contingencies without undue impairment of grid reliability, but it is important that the NPP operator know when the transmission system near the NPP can no longer sustain NPP voltage based on the TSO’s analysis of a N-1 of contingencies. This knowledge helps the operator understand the general condition of the NPP offsite power system. To satisfy the maintenance rule, the NPP operator should know the grid’s condition before taking a risk- significant piece of equipment out-of-service, and should monitor it for as long as the equipment remains out-of-service. Grid reliability evaluations should be performed as part of the maintenance risk assessment required by 10 CFR 50.65(a)(4). To perform meaningful and comprehensive grid reliability evaluations it is essential that the NPP licensee communicate with the TSO before and periodically during the performance of any grid-risk-sensitive activities. The communication between the NPP operator and grid TSO should enable the NPP operator to obtain up-to-date information on