Document: NUREG-0800
Document ID: e75b7685-2a36-4e9b-a431-02d166dcf372
Document Type: srp
Title: LOSS OF NONEMERGENCY AC POWER TO THE STATION AUXILIARIES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070681.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.2.6
CFR Part: 
CFR Title: 

Content:
REVIEW RESPONSIBILITIES Primary - Reactor Systems Branch (RSBSRXB ) 1 Secondary - None I. AREAS OF REVIEW The loss of nonemergency ac power is assumed to result in the loss of all power to the station auxiliaries. This situation could result either from a complete loss of the external grid (offsite) or a loss of the onsite ac distribution system. It is different from the loss of load condition considered in Standard Review Plan (SRP) Section 15.2.2 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 simultaneously tripped by the initiating event. This causes a flow coastdown as well as a decrease in heat removal by the secondary system. Within a few seconds the turbine trips and the reactor coolant system is isolated, causing the pressure and temperature of the coolant to increase. A reactor trip is initiated. The diesel generators are automatically started 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 core isolation cooling system in a boiling water reactor (BWR), emergency core cooling system (BWR), and auxiliary feedwater system in a pressurized water reactor (PWR). DRAFT Rev. 2 - April 1996 15.2.6-2 The review of the loss of ac power transient includes the sequence of events, the analytical model, the values of parameters used in the analytical model, and the predicted consequences of the transient. The sequence of events described in the applicant's safety analysis report (SAR) is reviewed by both RSBSRXB and the Instrumentation and Controls Systems Branch (ICSBHICB ). The 2 3 RSBSRXB reviewer concentrates on the need for the reactor protection system, the engineered 4 safety systems, and operator action to secure and maintain the reactor in a safe condition. The analytical methods are