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:
be more than the time previously evaluated for the SBO rule. The staff considers that a replacement (i.e., supplemental) AC power source is needed to back up an inoperable EDG or offsite power source during an extended AOT to maintain the defense-in-depth of the electrical power sources. The staff has previously granted AOT extensions to those licensees who have installed an alternate alternating current (AAC)2 power source (i.e., additional diesels, gas or combustion turbines, hydro units, or other power sources) credited for 1. By “cold shutdown” it is not implied that the plant needs to go to cold shutdown during LOOP. The unit can remain in either hot shutdown or hot standby in accordance with its licensing basis for the short term. However if the offsite power is not recovered in a timely manner it may become necessary for the unit to go to cold shutdown, therefore the supplemental or AAC power source must have the capacity and capability to accomplish this function if needed. 2. The AAC power source is a supplementary AC power source, such as non-safety diesel or gas turbine that can be substituted as a replacement power source for an EDG to power one train of LOOP loads to take the plant to cold shutdown if necessary. 8-8-4 Initial - February 2012 SBO events which can be substituted for an inoperable EDG in the event of a LOOP, provided the power source has enough capacity to carry all LOOP loads to bring the unit to a cold shutdown without any load shedding. In order to facilitate approval of an extended AOT for onsite or offsite power source, some licensees have provided a detailed PRA risk-informed evaluation and installed commercial-grade diesel generators capable of supplying power to the required safe-shutdown loads on the train removed from service 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