Document: NUREG-0800
Document ID: 8e754440-b70e-4b8a-9816-b4a64b631220
Document Type: srp
Title: Initial – February 2012
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1136/ML113640138.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8
CFR Part: 
CFR Title: 

Content:
for the maintenance outage. Some licensees at multi-unit sites have qualified their existing EDGs as an AAC source for meeting the SBO rule requirements (see Reference 5 for qualifications of the AAC source). For existing Class 1E EDGs to qualify as a supplemental AC source in the adjacent unit (provided with cross- connection within the same division of loads) for extending the AOT, the EDGs must have excess capacity to meet their unit’s LOOP safe shutdown loads (without load shedding) while complying with the single failure criteria, and have spare capacity to support the other unit in maintenance to bring the plant to cold shutdown without any load shedding. The permanent or temporary power source can be either a diesel generator, gas or combustion turbine, or power from nearby hydro units. This source can be credited as a supplemental source, that can be substituted for an inoperable EDG during the period of extended AOT in the event of a LOOP, provided the risk-informed and deterministic evaluation supports the proposed AOT and the power source has enough capacity to carry all LOOP loads to bring the unit to a cold shutdown. Multi-unit sites that have installed a single AAC power source for SBO cannot substitute it for the inoperable diesel when requesting AOT extensions unless the AAC source has enough capacity to carry all LOOP loads to bring the unit to a cold shutdown as a substitute for the EDG in an extended AOT and carry all SBO loads for the unit that has an SBO event without any load shedding. The staff rationale is that if LOOP should occur during the period of extended AOT, the single AAC power source for SBO must be dedicated to the unit without the extended AOT to meet the SBO rule. Therefore for the unit in extended AOT, the licensee must provide a permanent or a temporary power source as a substitute for the EDG in an extended AOT to maintain the same level of defense-in-depth for safe shutdown of the plant. The staff believes that relying on