Document: NUREG-0800
Document ID: 81256f55-72dd-4777-9472-f373c71c4554
Document Type: srp
Title: AC POWER SYSTEMS (ONSITE)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550065.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
the reliability and redundancy of emergency onsite ac power sources must be used as a factor in determining the duration for which the plant must be capable of coping with a station blackout event. A reliability program should also be provided to attain and maintain the target reliability levels of emergency onsite ac sources with respect to station blackout considerations. Regulatory Guides 1.9 and 1.155, and SRP Section 8.4 describe guidance acceptable to the staff for meeting the requirements of 10 CFR 50.63 related to addressing emergency onsite ac source reliability for station blackout. Determination of station blackout coping time is reviewed in detail in SRP Section 8.4. As documented in SECY 94-084, the electrical distribution system for evolutionary light water reactor design plants should include: 1) an alternate offsite power source available for non-safety-related loads, unless the design margins for loss of non-safety-related loads are no more severe than turbine-trip-only events in current plants, and 2) at least one offsite circuit to each redundant safety division supplied directly from offsite power sources, with no intervening non-safety-related buses. For passive reactor design applications, such as the AP1000, the potential risk contribution of a station blackout is minimized by not needing ac power sources for design-basis events. The safety-related passive systems in these plants do not need any ac power sources to perform safety-related functions. They are designed to automatically establish and maintain safe shutdown conditions after design basis events for 72 hours, without operator action, following a loss of both onsite and offsite ac power 8.3.1-19 Revision 3 - March 2007 sources. Consequently, a passive reactor design meets the requirements of 10 CFR 50.63 if it can establish and maintain safe shutdown conditions for the specified duration of the station blackout event, without operator action, following a loss of both onsite and