Document: NRC Regulatory Guide
Document ID: c256f223-ee35-43e0-82e7-aa7b14469259
Document Type: regulatory_guide
Title: Preoperational Testing of Emergency Core Cooling Systems for Pressurized Water Reactors + HISTORY - HISTORY DG-1253 , Proposed Revision 2 (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1101/ML110110480.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.79
CFR Part: 
CFR Title: 

Content:
nt of the most limiting single failure occurring coincident with, or during, the event. The SIS, in conjunction with the rapid insertion of the control rod cluster assemblies (reactor scram), provides protection during the following events: a. loss-of-coolant accident (LOCA), b. ejection of a control rod cluster assembly, c. secondary steam system piping failure, d. inadvertent opening of main steam relief or safety valve, and e. steam generator tube rupture. A.3 U.S. Evolutionary Power Reactor Safety Injection System The ECCS for the U.S. Evolutionary Power Reactor (U.S. EPR) is the SIS (Figure A.3-1). Figure A.3-1. U.S. EPR Safety Injection System Appendix A to DG-1253, Page A-3 The SIS consists of four independent trains, designated trains 1, 2, 3, and 4, one supplying each reactor coolant loop. The four trains are separated into four safety divisions and are functionally identical. Each SIS train has separate MPSI and LPSI pump trains and an accumulator injection train. The MPSI and LPSI pump trains share an isolable suction line from the in-containment refueling water storage tank (IRWST). This three-way valve aligns the IRWST to both the MPSI and LPSI pump suctions when in the open position. The LPSI pump train includes a heat exchanger and a suction line from the reactor coolant system (RCS) hot leg for residual heat removal, which can be realigned for LPSI hot-leg injection. The discharge lines for all three MPSI, LPSI, and accumulator injection trains branch together to share an injection nozzle on their associated RCS cold leg. Cross-connects between trains 1 and 2 and between trains 3 and 4, which are normally isolated by two motor-operated valves in series to maintain train separation, allows removal of individual trains from service for maintenance. Each cross-connect provides an alternate injection path for the train that remains in service. This configuration mitigates the effect of degraded safety injection caused by steam entrainment during a LOCA,