Citation

Heising CD, Guey CN. Reliab. Eng. 1984; 8(2): 101-116.

Copyright

(Copyright © 1984, Elsevier Publishing)

DOI

10.1016/0143-8174(84)90058-1

PMID

unavailable

Abstract

The beta factor method for calculating common cause failures has been used in many probabilistic risk analyses to evaluate redundant systems reliability. The multiple dependent failure fraction (MDFF) method is a generalization of the beta factor (BF) method, and is extended here to derive reliability expressions for several multiple redundant systems. To demonstrate the difference in results that can arise by applying these methods, two example systems were analyzed consisting of reactor safety systems made up of two and three redundant trains (the high pressure injection and auxiliary feedwater systems). It is shown that the MDFF method is less conservative and produces more realistic calculations of system unavailability by factors of between two and 20 for the two versus three train systems, respectively. Additionally, both approaches produce higher values than does an analysis that excludes common cause effects, indicating that system unavailability may be grossly underestimated by several orders of magnitude if common cause effects are neglected. For these reasons, it is recommended that the MDFF method be utilized in redundant systems analysis as it produces more realistic results.