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:
regulatory guide, Position C.1.3.1.1 states the following: The design of the ECCS and containment heat removal system should ensure that sufficient NPSHa is provided to the system pumps, assuming the maximum expected temperature of the pumped fluid and no increase in containment pressure from that present before the postulated LOCA. Also in this regulatory guide, Position C.1.3.1.2 states the following: For certain operating reactors in which it is not practicable to alter the design, conformance with Section C 1.3.1.1 may not be possible. In these cases, the determination of NPSHa should not include containment pressure above that which is necessary to preclude pump cavitation. In the determination of NPSHa for this situation, the calculation of available containment pressure and sump/pool water temperature as a function of time should underestimate the expected containment pressures and overestimate the sump/pool water temperatures. In a letter dated March 18, 2009 (Ref. B-3), to the U.S. Nuclear Regulatory Commission (NRC) Executive Director for Operations, the Advisory Committee on Reactor Safeguards (ACRS) questioned the use of containment pressure higher than the containment pressure before the accident in determining the NPSHa. This letter also references previous correspondence from the ACRS on this subject. In discussions with the NRC staff, the ACRS recommended quantifying the uncertainty in the calculations used to verify the acceptability of using CAP in determining NPSH margin. As part of the safety analysis to confirm that the pumps will perform their safety functions, licensees should demonstrate that the ECCS and containment heat removal pumps will have adequate NPSH margin following the occurrence of a postulated accident. The use of CAP is acceptable to the NRC if the licensee demonstrates that the CAP used in the calculation of NPSH margin is less than or equal to the calculated CAP available at that time in the postulated accident. For the