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:
ants on the loss of required onsite power sources may differ from those recommended in this guide and should be evaluated on a case-by-case basis. Operational Restrictions The operational restrictions (based on the intent of GDC-17) in the technical specifications are based on the following three assumptions: 1. Meeting the Limiting Conditions for Operation The LCOs of NPPs are met when all LCO-required electric power sources are determined to be operable in accordance with the applicable plant-specific technical specifications at the required voltage and capacity for the nuclear station and capable of withstanding a “worst case” transmission system contingency (also known as the N-1 contingency). 2. Period of Continued Operation Under certain conditions, it may be prudent to complete any actions required by technical specifications and continue operation at power for a limited time not to exceed the plant-specific completion time allowed by the technical specifications rather than to implement an immediate shutdown upon loss of some required electric power circuits. Such decisions should be based on an evaluation of the safety significance associated with immediate shutdown against those associated with continued operation. For example, if the immediate shutdown will cause the offsite power source to become inoperable or otherwise cause transmission system degradation, the nuclear plant operator may conclude that continued power operation is a safer overall course of action provided that all actions required by the technical specifications are completed in the required completion time. The plant may delay shutdown up to the maximum time allowed by technical specifications provided that these activities do not risk further degradation of the electric power system or in any way jeopardize plant safety. If an immediate shutdown is determined to be the safer course of action, the plant should commence an orderly shutdown in parallel with efforts to restore the