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:
ons, care has to be taken when the application relies on assessing the impact on risk of having one train unavailable. In this case, the effective success criterion of the remaining part of the system changes, so that in the case of the one-out-of-four system, a CCF of three SSCs becomes a possible contributor. The impact of not modeling the lower-order CCF contributors should be investigated. Note that this can impact applications for which the justification of the change relies on risk categorization, as well as those that require an evaluation of changes to risk. c. Evaluation Findings Evaluation findings should include statements to the following effect: Common cause failure has been suitably addressed, and the licensee has systematically identified component groups sharing attributes that correlate with CCF potential and that affect the application. Where applicable, the licensee's performance monitoring program addresses a phased implementation approach to reduce the potential for increased incidence of CCFs attributable to the proposed change. SRP 19-A15 A.8 Modelinq of Human Performance a. Areas of Review The results of a PRA, and therefore the input it provides to risk-informed decisionmaking, can be very strongly influenced by the modeling of human performance. Plant safety depends significantly on human performance, 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) fbr 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