Document: NRC Regulatory Guide
Document ID: 6f0a99f2-d25a-44e3-b7f2-3286449a9752
Document Type: regulatory_guide
Title: Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant Accident (Rev. 5)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2126/ML21266A185.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.82
CFR Part: 
CFR Title: 

Content:
rate should be between NPSH margin ratios of 1.2 and 1.6. For pumps of very high suction energy, the permissible time in this range should be limited unless operating experience, testing, or analysis justifies a longer time. Realistic calculations should be used to determine the time within this band of NPSH ratio values. B-9.8 BWR licensees proposing to calculate NPSHa using CAP greater than the containment pressure before the postulated accident should follow the procedure in NEDC-33347P-A, which essentially determines whether a higher pressure is needed to ensure NPSHa ≥ NPSHr using conservative assumptions. If so, Monte Carlo calculations determine the 95/95 value of Hww. This value is used to determine NPSHa, along with conservative values of hloss and hstatic (determined separately). The flowchart in Figure B-7 illustrates the process. For PWRs, the following are acceptable options for calculating NPSHa using CAP greater than the containment pressure before the postulated accident: (1) use the vapor pressure corresponding to the sump water temperature, or (2) use a procedure similar to the BWROG Monte Carlo procedure. DG-1385, Appendix B, Page B-26 B-9.9 The necessary mission time for a pump using CAP should include not only the duration of the accident, when the NPSH margin may be limited, but also any time after recovery from the accident during which pump operation is needed to maintain the reactor or containment in a stable, cool condition; during this time, the NPSH margin may be much greater. This additional time is usually 30 days. DG-1385, Appendix B, Page B-27 ACRONYM LIST 10 CFR Title 10 of the Code of Federal Regulations ACRS Advisory Committee on Reactor Safeguards ADAMS Agencywide Documents Access and Management System ANSI American National Standards Institute ASME American Society of Mechanical Engineers ATWS anticipated transient without scram BWR boiling-water reactor BWROG Boiling Water Reactor Owners’ Group CAP containment accident