Document: NRC Regulatory Guide
Document ID: 82659041-98b0-4721-b25d-c4fb2ea394d0
Document Type: regulatory_guide
Title: An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1635/ML16358A153.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.174
CFR Part: 
CFR Title: 

Content:
bly higher than 10-5 per reactor year, the focus should be on finding ways to decrease rather than increase it. Such an indication would result, for example, if (1) the contribution to LERF calculated from a limited scope analysis, such as the IPE or the IPEEE, significantly exceeds 10-5, (2) a potential vulnerability has been identified from a margins-type analysis, or (3) historical experience at the plant in question has indicated a potential safety concern. • When the calculated increase in LERF is in the range of 10-7 per reactor year to 10-6 per reactor year (i.e., the increase in LERF falls within Region II of Figure 5), applications are considered only if it can be reasonably shown that the total LERF is less than 10-5 per reactor year. • Applications that result in increases to LERF above 10-6 per reactor year (i.e., the increase in LERF falls within Region I of Figure 5) would not normally be considered. These guidelines are intended to provide assurance that proposed increases in CDF and LERF are small and are consistent with the intent of the Commission’s Safety Goal Policy Statement. As illustrated in footnote to Figures 4 and 5, the boundaries between regions are not definitive. In particular, in applying these guidelines, it is important to recognize that the risk metrics calculated using PRA models are a function of the assumptions and approximations made in the development of those models. This is DG-1285, Page 30 particularly important when the results from PRA models for multiple hazard groups are combined since the results from some hazard groups, depending on the state of practice, may be conservatively or non- conservatively biased. This is discussed further in Section C.2.5. Section C.6.3.2 provides a discussion on tracking cumulative changes. As indicated by the shading on the acceptance guideline figures, the change request is subject to an NRC technical and management review that becomes more intensive as the calculated results move