Document: NUREG-0800
Document ID: b8d2b8f5-432a-4c0a-81ab-20231f7d0f28
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT EVALUATION FOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1508/ML15089A068.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
bability that a failure will be tolerated for the types of failures that were tested. Fault coverage is a function of the failures that were used in testing. It is essential that the reviewer be aware of the types of failures that were used in testing to apply a value of fault coverage to a PRA model. How fault coverage is measured and defined should be evaluated by the risk analyst in conjunction with the I&C reviewer. E. If a DI&C system shares a communication network with other DI&C systems, the effects on all systems due to failures of the network should be modeled jointly. The impact of communication faults on the related components or systems should be evaluated, and any failure considered relevant should be included in the probabilistic model. F. If hardware, software, and system CCF probabilities are treated together in the PRA and if the applicant uses standard methods such as the multiple Greek letter method, alpha factor method, or beta factor method to model DI&C system CCFs, an NRC audit of these calculations, their bases, and the modeling assumptions may be warranted. G. The data for hardware failure rates (including CCF) will likely be more robust than the software failure data. Review of applicant claims regarding data should be proportional to the use made of the PRA results. If limited use is made, limited review is necessary. If the applicant claims CCF rates that are more than an order of magnitude lower than other component groups (especially for software), an NRC audit of data calculations may be warranted. Data (either public or system-specific) have been a limiting factor in the evaluation of risk for DI&C systems. The guidelines in Subsection 4.5.6, “Data Analysis,” of the ASME Standard for PRA, ASME/ANS RA-Sa-2009, for nuclear power plant applications should be satisfied consistent with the clarifications and qualifications of RG 1.200. Determine if the process used to determine basic event probabilities is reasonable. Check the