Initial guidance on digraph-matrix analysis for systems interaction studies. [PWR; BWR]

This report describes the digraph-matrix analysis for systems structural analysis. The method is useful to analysts that are searching for both single failures and paired failures that disable systems. The digraph-matrix analysis can assure the analyst that the independent functioning of a safety system is not jeopardized by design features that cause faults to be dependent. The digraph-matrix analysis facilitates the discovery and the quantification of component reachability. The guidance is sufficiently specific that the reader can make direct application. Because a systems interaction analysis of an LWR is expensive, the resource efficiency of a candidate method is important to the staff. A demonstration of the digraph-matrix analysis is part of the staffs efforts to provide a measure of its resource efficiency. Additionally, there are features within the digraph-matrix analysis itself that might be modified to enhance resource efficiency.