Document: NUREG-0800
Document ID: ac43f632-9db1-4857-9f56-bfba45965456
Document Type: srp
Title: * These are modifications to a plant’s design, operations, or other activities that require NRC approval. These modifica
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0232/ML023250195.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19
CFR Part: 
CFR Title: 

Content:
, so it is essential that the PRA treat it carefully. However, the modeling of human performance, typically referred to as human reliability analysis (HRA), is a relatively difficult area; significant variations in approach continue to be encountered, and these can yield significantly different estimates of human error probabilities (HEPs) for what appears to be similar human failure events. The particular values used for HEPs can significantly influence 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 that 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 the frequency in an implicit way. b. Review Guidance and Procedures Reviewers should understand the potentially significant human performance issues that might be affected by the application 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