Document: NUREG-0800
Document ID: a2680f96-0e15-402d-89ab-688ff09806a8
Document Type: srp
Title: with respect to the specified station blackout event/duration.13
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070497.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.2
CFR Part: 
CFR Title: 

Content:
ency ac power source nor the redundant emergency ac power source. Therefore, a single unit requiring one emergency ac source for safe shutdown should have at least three EDGs, with one EDG that may be designated as the AAC power source meeting Regulatory Guide 1.155 guidance for AAC power sources. (3) At multi-unit sites, where the combination of emergency ac sources exceeds the minimum redundancy requirements (on a per nuclear unit basis) for normal safe shutdown of all units, the excess emergency ac power sources may be used as alternate ac power sources, provided they meet the AAC power source criteria of Regulatory Guide 1.155, Position DRAFT Rev. 4 - April 1996 8.2-26 C.3.3.5. If no emergency ac power source in excess of the minimum redundancy requirements remains, the occurrence of station blackout must be assumed for all of the units. (4) When a station blackout occurs at one unit of a multi-unit site, the emergency ac power source(s) and the redundant emergency ac power source(s) are unavailable. A station blackout on one unit does not assume a concurrent single failure; however, the remaining unit(s) must still meet the normal operating single failure criteria. Therefore, an EDG could be designated as an AAC only if (a) the EDG is neither the required emergency ac power source nor the redundant emergency ac power source for the unit experiencing the station blackout and (b) the EDG is not required as an emergency or redundant emergency ac 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 licensee's or applicant's station onsite ac power system should determine whether such a capability exists. (5) Table 1 provides guidance for determining the availability of an EDG for use as an AAC power source. (6) Emergency diesel generators with 1-out-of-2 (shared) and 2-out-of-3 (shared) ac power configurations may not be used as AAC power