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:
ty analyses that demonstrate adequate core and containment cooling. This ensures that the safety analyses and the NPSH analysis are consistent. If the CAP used is determined assuming that NPSHa equals NPSHreff, then the pump flow rate used in the core and containment cooling calculations should be equal to or less than the flow rate Q3% (instead of Qnormal) resulting from a 3-percent decrease in pump TDH. Figure B-12 illustrates this. Figure B-12 Illustration of flow rate (≤Q3%) to be used in safety analysis if NPSHa = NPSHreff DG-1385, Appendix B, Page B-23 Duration of the Need for Containment Accident Pressure As stated above, based on pump performance considerations, the time for operation in the region of maximum cavitation erosion should be limited. In addition, in relation to containment integrity, the duration of the need for CAP to maintain acceptable NPSHa is, in general, not risk significant. Therefore, no time limit based on containment integrity is necessary, since such factors as preexisting leaks or failure to isolate the containment upon receipt of a containment isolation signal dominate risk and are independent of the time interval during which CAP is used. Loss of Containment Isolation and Containment Leakage A loss of containment isolation that could compromise containment integrity should be considered. Possible losses of containment integrity include containment venting required by procedures and loss of containment isolation due to a postulated Appendix R fire. Licensees should conservatively demonstrate that, for the plant examined, loss of containment integrity from these causes cannot occur or will occur only after use of CAP is no longer needed. The following discussion is not considered a primary concern for plants in which containment pressure equals the vapor pressure corresponding to the temperature of the suppression pool (for BWRs) or sump pool (for PWRs). To reduce the likelihood of a preexisting leak in containment, licensees