Document: NRC Regulatory Guide
Document ID: de79d411-4fc9-456e-a5a0-f4a910ca4c9a
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating a Control Rod Ejection Accident for Pressurized Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2111/ML21119A157.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.77
CFR Part: 
CFR Title: 

Content:
of 1.2 per hour) decrease by a factor of two. In other words, the weights are appropriately adjusted for the actual fresh-air exchange rate. CRs with automatic isolation capabilities may have leakage characteristics different from those listed in Table 2. Again, appropriate adjustments of weight should be made based on the actual air exchange rate. The use of an ACH less than 0.06 should have a periodic test to validate the low leakage rate. Varying Metrology Stability Category Varying meteorology stability category is not a linear extrapolation like the examples above. Three weighting factors are provided in Table A-1. If the meteorology was out of the Category F condition, for better (i.e., Category E) or for worse (i.e., Category G), then the tabulated values 2.5 and 0.4 could be used for adjusting the new weight limiting value for Table 2.If there is no change from Category F condition, then the multiplication factor is a unity. Note that in RG 1.78, Revision 1,the Category F Pasquill stability class did represent the worst 5th-percentile meteorology observed at the majority of the NPP sites. DG-1387, Appendix A, Page A-2 Table A-1. Factors for Varying Meteorology Category Pasquill Stability Category Weighting Factor A B C D E F G -- -- -- -- 2.5 1 0.4 There are no relevant constant or variable factors for Categories from A to D. Please consult with the local meteorologist if desired.