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:
redundancy; however, the remaining trains of the inverter power system have full functional capability to prevent a reactor trip. Because a subsequent single failure of another inverter could cause a reactor trip, the licensee should severely restrict the time allowed for continued operation. If the affected inverter is restored within this time period, unrestricted operation may resume. If not, the unit should promptly be brought to an orderly shutdown. C. REGULATORY POSITION The completion times provided in this section of the regulatory guide reflect an acceptable regulatory practice for designs with two or more onsite ac sources, two or more dc power sources, inverters, and two offsite power sources. These completion times also appear in the iSTS (Refs. 1–5). The plant-specific technical specifications identify specific required action completion times. Additionally, the regulatory positions in this section are based on the grid operator’s capability to ensure the adequacy of the offsite power system through contingency analyses and plant design features and on the licensee’s ability to manage risk-significant maintenance and surveillance activities. The intent of each of the following regulatory positions is to ensure that an NPP is in an acceptably safe operating mode whenever the available electric power sources are less than the technical specification LCO. Accordingly, this section discusses the seven levels of degradation of the electric DG-1244, Page 9 power system in order of increasing degradation; the technical specifications specify the required actions and the required action completion time for each degraded level. Whenever the technical specifications allow unrestricted operation to resume, such resumption should be contingent on the verification of the capability of the restored sources. Similarly, whenever the technical specifications allow power operation to continue during a specific degradation level, such continued power operation