Document: NUREG-0800
Document ID: ac4cde5a-7464-48b8-9067-860c672cbb68
Document Type: srp
Title: STATION BLACKOUT
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550061.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.4
CFR Part: 
CFR Title: 

Content:
power source and the redundant EAC power source are unavailable. An EDG may be designated as an AAC power source only if that EDG is neither the necessary EAC power source nor the redundant EAC power source. Therefore, a single unit requiring one EAC source for safe shutdown should have at least three EDGs, with one EDG that may be designated as the AAC power source meeting RG 1.155 guidance for AAC power sources. iii. At multiunit sites, where the combination of EAC sources exceeds the minimum redundancy criteria (on a per-nuclear-unit basis) for normal safe shutdown of all units, the excess EAC power sources may be used as AAC power sources, provided they meet the AAC power source guidance in Section C.3.3.5 of RG 1.155. If no EAC power source in excess of the minimum redundancy criteria remains, the occurrence of SBO must be assumed for all of the units. iv. When an SBO occurs at one unit of a multiunit site, the EAC power source(s) and the redundant EAC power source(s) are unavailable. An SBO on one unit does not assume a concurrent single failure; however, the remaining unit(s) should still meet the normal operating single failure criteria. Therefore, an EDG could be designated as an AAC only if (1) the EDG is neither the necessary EAC power source nor the redundant EAC power source for the unit experiencing the SBO and (2) the EDG is not necessary as an emergency or redundant EAC power source for the remaining units. Where an EDG is used as an AAC, it is desirable that the EDG be connectable to all buses essential for normal safe shutdown. Review of the applicant’s station onsite ac power system should determine whether such a capability exists. v. Multiunit sites may not use EDGs with 1-out-of-2 (shared) and 2-out-of-3 (shared) ac power configurations as AAC power sources. vi. For EDGs used as an AAC source, the engine support systems should conform with the relevant criteria used to evaluate them under SRP Sections 9.5.4 through 9.5.8. 4. Procedures and