Document: NRC Regulatory Guide
Document ID: 22ccfd5e-c5d8-4615-a02c-32369aa9f533
Document Type: regulatory_guide
Title: Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1930/ML19308B636.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.200
CFR Part: 
CFR Title: 

Content:
ation of CDF and LERF/LRF integrates - the seismic hazard - the seismic fragilities - the systems analysis DG-1362, Page 27 Technical Elements for Screening and Conservative Analysis of Hazards for an At-Power PRA Screening methods can often be employed to show that the contribution of a hazard to CDF and/or LERF/LRF is not significant. Criteria that have been recognized for screening out are the following: A hazard can be screened out either (1) if it meets the criteria in the NRC’s 1975 SRP or a later revision; or (2) if it can be shown using a demonstrably conservative analysis that the mean value of the design-basis hazard used in the plant design is less than 10-5 per year and that the conditional core damage probability is less than 10-1, given the occurrence of the design-basis-hazard event; or (3) if it can be shown using a demonstrably conservative analysis that the CDF is less than 10-6 per year. It is recognized that for those new reactor designs with substantially lower risk profiles (e.g., internal events CDF below 10-6 per year), the quantitative screening value should be adjusted according to the relative baseline risk value. Screening and Conservative Analysis is usually the first task an analyst performs when developing a base PRA. Natural and human-caused hazards that apply to the site under consideration are first identified. Table D-1 in Appendix D provides a list of hazards that should be addressed in the base PRA. Many of the hazards in Table D-1 may be eliminated from a detailed PRA if they can be screened out based on the screening criteria defined above. A preliminary screening, using a defined set of screening criteria, is used to eliminate risk contributors matching the criteria from further consideration. Further screening can be performed by using a bounding or demonstrably conservative analysis with defined quantitative screening criteria to demonstrate that the risk from some external events is sufficiently low to eliminate them from