Document: NUREG-0800
Document ID: e47fd320-f3af-41cd-883e-a51e0949005d
Document Type: srp
Title: to verify that the AAC source (or sources) will not adversely affect the
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1007/ML100740424.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.2
CFR Part: 
CFR Title: 

Content:
system should meet or exceed 95 percent as determined in accordance with NSAC-108 (Ref. 37) or equivalent methodology. O. Where EDGs are identified as AAC power sources, they should meet the following criteria: i. At single unit sites, any EAC power source(s) in excess of the number required to meet the minimum redundancy criteria (i.e., single failure) for safe shutdown may be assumed to be available. These EAC power sources may be designated as AAC power sources, provided the guidelines identified in Section C.3.3.5 of RG 1.155 are met. 8.4-16 Revision 1- May 2010 ii. A single unit that needs one EAC source to place the plant in safe shutdown needs one redundant EAC power source. For SBO, both the EAC 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