Document: NUREG-0800
Document ID: 621763b9-bd48-4ded-8c42-b942a23a06d4
Document Type: srp
Title: – 15.2.5
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070680.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.2.1
CFR Part: 
CFR Title: 

Content:
LOSS OF EXTERNAL LOAD; TURBINE TRIP; LOSS OF CONDENSER VACUUM; CLOSURE OF MAIN STEAM ISOLATION VALVE (BWR); AND STEAM PRESSURE REGULATOR FAILURE (CLOSED) REVIEW RESPONSIBILITIES Primary - Reactor Systems Branch (RSBSRXB)1 Secondary - None I. AREAS OF REVIEW A number of transients initiating events which are expected to occur with moderate frequency 2 result in unplanned decreases in heat removal by the secondary system. Each transient event3 covered in this Standard Review Plan (SRP) section should be discussed in individual sections 4 of the safety analysis report (SAR), as required by the Standard Format (Ref. 1) specified in Regulatory Guide 1.70. The transients initiating events and associated transients to be 5 6 evaluated are: 1. Loss of External Load In a loss of external load event, an electrical disturbance causes loss of a significant portion of the generator load. This loss of load situation is different from the loss of ac power condition considered in Standard Review Plan (SRP) Section 15.2.6 in that offsite ac power remains 7 available to operate the station auxiliaries (such as reactor coolant pumps). The onsite emergency diesel generators are therefore not required for the loss of external load transient event. Immediate fast closure of the turbine control valves (TCVs) and intercept valves is DRAFT Rev. 2 - April 1996 15.2.1-2 initiated whenever a loss of generator load takes place. For a boiling water reactor (BWR), a fast TCV closure (0.150–0.2 sec) causes a sudden reduction in steam flow and results in a reactor pressure surge. For a BWR without select rod insert (SRI), reactor scram occurs. For a pressurized water reactor (PWR) there is also a sudden reduction in steam flow, and this causes the pressure and temperature in the shell side of the steam generator to increase. The latter effect, in turn, results in an increase in reactor coolant temperature, a decrease in coolant density, an increase in water volume in the pressurizer, and an