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
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Content:
luence results of the assessment of the impact of a proposed change. In addition to the quantification issue, there are questions related to what kind of human actions can appropriately be credited in the context of a particular regulatory finding. As an example, suppose that PRA results appear to support relaxation of requirements for a component based on the argument that even if the component fails, its failure can be recovered with high probability by operator actions outside the control room. The issues of concern here are whether the modeling of the operator action and the evaluation of the failure probability is appropriate, and whether this kind of credit is the sort of compensating measure that is intended by staff guidance to support justification of a relaxation. One further issue involves the impact of human performance which is not explicitly modeled, but is implicit in certain parameter values. An example is the influence of human performance on initiating event frequency. The causes of initiating events are typically not addressed; their impact is included in 1he frequency in an implicit way. b. Review Guidance and Procedures Reviewers should understa-id the potentially significant human performance issues that might be affected by the a-ipplication and how these are reflected in the PRA. This understanding requires a review of the approach used to estimate human error probabilities. The HRA can impact the assessment of the change in several ways. First, the change may directly affect the human failure events (HFEs). Second, the HFEs may represent responses to failures of the SSCs impacted by the change. Finally, HFEs unrelated to the change can obscure or exaggerate the impact of the change (depending on their values) by inappropriately increasing or decreasing the value of the accident sequences unaffected by the change. When the change directly impacts the HFEs (e.g., as a result of a procedure change or a change in operating practice), reviewers