Document: NUREG-0800
Document ID: 598d070d-fb96-43ce-ad4f-27f14623be46
Document Type: srp
Title: NUREG-0800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350119.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15
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Content:
NUREG-0800 (Formerly NUREG-75/087) .U.S. NUCLEAR REGULATORY COMMISSION Z STANDARD REVIEW PLAN OFFICE OF NUCLEAR REACTOR REGULATION 15.2.1-15.2.5 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 (RSB) Secondary - None I. AREAS OF REVIEW A number of transients which are expected to occul with moderate frequency result in unplanned decreases in heat removal by the secondary system. Each transient covered in this SRP section should be discussed in individual sections of the safety analysis report (SAR), as required by the Standard Format (Ref. 1). The transients to be evaluated are: 1. Loss of External Load In a loss of external load event an electrical disturbance causes loss of a signif- icant 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 available to operate the station auxiliaries (such as reactor coolant pumps). The onsite emergency diesels are therefore not required for the loss of external load transient. Immediate fast closure of the turbine control valves (TCV) and intercept valves is 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 increase in reactor coolant pressure. For a PWR with