Document: NUREG-0800
Document ID: 824740ba-eb51-4b24-bd6f-df01c35d75f3
Document Type: srp
Title: LOSS OF NONEMERGENCY AC POWER TO THE STATION AUXILIARIES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550008.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.2.6
CFR Part: 
CFR Title: 

Content:
REVIEW RESPONSIBILITIES Primary - Organization responsible for review of transient and accident analyses for PWRs/BWRs Secondary - None I. AREAS OF REVIEW The loss of nonemergency alternating current (ac) power is assumed to result in the loss of all power to the station auxiliaries. This situation, which could be the result of a complete loss of either the external (offsite) grid or the onsite ac distribution system, is different from the loss of load condition considered in Standard Review Plan (SRP) Section 15.2.1-15.2.5 because, in the latter case, ac power remains available to operate the station auxiliaries. The major difference is that in the loss-of-ac-power transient, all the reactor coolant circulation pumps are tripped simultaneously by the initiating event, resulting in a flow coast-down as well as a decrease in heat removal by the secondary system. Within a few seconds, the turbine trips, the reactor coolant system is isolated, and the pressure and temperature of the coolant increase. A reactor trip is initiated. The diesel generators start automatically and provide electric power to the vital loads. The sensible and decay heat loads are handled by actuation of the steam relief system, steam bypass to the condenser, reactor 15.2.6-2 Revision 2 - March 2007 core isolation cooling system in a boiling-water reactor (BWR), emergency core cooling system, and auxiliary feedwater system in a pressurized-water reactor (PWR). The loss of ac power has the following effects: (i) An immediate load rejection with fast closure of the turbine control valves, (ii) loss of power to the condensate and feedwater pumps, resulting in loss of feedwater, and (iii) the reactor is isolated after loss of main condenser vacuum. Therefore, the review of the loss-of-ac-power transient includes the sequence of events, the analytical model, the values of parameters in the analytical model, and the predicted consequences of the transient. The specific areas of review are as follow: 1.