Circuit Analysis: Failure Mode and Likelihood Analysis (NUREG/CR-6834, SAND2002-1942P)
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Manuscript Completed: June 2003
Date Published: September 2003
J.L. LaChance, S.P. Nowlen, F.J. Wyant, V.J. Dandini
P.O. Box 5800
Sandia National Laboratories
Albuquerque, New Mexico 87185-0748
H.W. Woods, NRC Project Manager
Division of Risk Analysis and Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code Y6037
Under existing probabilistic risk assessment (PRA) methods, the analysis of fire-induced circuit faults has typically been conducted on a simplistic basis. While exceptions do exist, a typical fire PRA will assume that given damage to any power or control cables, the associated circuits simply become unavailable. This approach does not address, for example, the potential that certain failures might cause spurious component actuations. In particular, certain cable failure modes, referred to as hot shorts, might lead to spurious operations. Those fire PRAs that have considered potential spurious operations have relied on methodologies that have significant uncertainties with regard to the scope of the assessments, the underlying methods, and the assumptions employed. Nonetheless, some of these fire PRAs have shown that cable hot shorts can be a significant risk contributor.
This report describes the results of a task to address weaknesses in existing fire PRA circuit analysis methods. An extensive review of available cable failure data has been performed and the current state of knowledge regarding cable failure modes and likelihood is characterized. A framework for advanced methods of cable failure mode and likelihood analysis is also presented. Advanced tools for performing PRA circuit analysis that explicitly treat different cable failure modes and the resulting circuit and system impact are outlined. Example applications of the proposed circuit analysis methods are provided.