Document: NUREG-0800
Document ID: e32f0820-4e33-476e-aa36-4ca8c2c64af0
Document Type: srp
Title: Use of Probabilistic Risk Assessment in Plant-Specific, Risk-Informed Decisionmaking:
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0119/ML011940192.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
tiple requirements could be relaxed on certain "low" significant components under multiple applications. If the QA (potentially affecting the failure rate) and the test interval (potentially affecting fault exposure time) were to be relaxed for the same component, the component unavailability could increase more than expected (since failure rate and fault exposure :irne combine multiplicatively in the calculation of unavailability). If the effects of QA on failure rate could be quantified convincingly, this would be addressed explicitly, but this cannot presently be ensured. As a result, potential exists that different applications might lead to unintended and unquantified synergistic effects on the unavailability of a given component. Synergistic effects on a given element can be addressed by showing that the basic event model adequately reflects the effects of programmatic activities, and that the calculated unavailability, propagated through the PRA, is consistent with the needed performance with regard to the risk indices and the defense-in-depth concept. However, it is more straightforward simply not: to allow for the relaxation of multiple programmatic requirements on a given component, unless demonstrable justification is provided that the risk contribution from the component is negligible for conditions covered by the set of requirements. For example, if IST is relaxed on a given component, it would be preferable not to relax QA as well, unless good arguments are given for allowing both. Risk Management One of the goals of the review should be to ensure that in the course of the licensee's engineering evaluations, principles of risk management are appropriately applied in the process of evaluating changes to current regulatory requirements. For the purposes of this SRP chapter, "risk management" refers to an approach to decisionmaking about safety that seeks to allocate available resources and worker dose in such a way as to minimize the risk to public