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:
combination of SSCs that fails the function of the system. For example, if system success is defined as success of one out of four components, usually only a single term representing a CCF of all four components is included. If the success criterion were two out of four, the corresponding CCF term would represent failure of any three or all four SSCs in the group. While probabilistically this usually corresponds to the dominant contributions, 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-A16 A.8 Modeling 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