Systems interaction analysis of the Clinch River Breeder Reactor Plant Shutdown Heat Removal System

Systems interaction analyses are an important extension to the Probabilistic Risk Assessment (PRA) method used in The Reactor Safety Study (WASH-1400) and in more recent PRAs. Systems interaction analyses allow the analyst to study the coupling of engineered safety features through shared support systems, common maintenance activities, and plant operational procedures. This type of analysis makes use of a modified fault tree, or systems interaction fault tree, which includes potential systems interaction candidates. A systems interaction candidate is a system which, if failed, would cause the components it supports to malfunction. Consequently, a systems interaction analysis will provide the analyst with previously unrecognized failure modes caused by support system failures.

This systems interaction analysis of the Clinch River Breeder Reactor Plant Shutdown Heat Removal System (CRBRP SHRS) demonstrates the application of systems interaction analysis methodology. The results of this analysis show that the CRBRP SHRS is not as redundant as previous studies have indicated. For example, previous studies have determined no one-event minimal cut set (single-failure point) and only one two-event minimal cut set (one double-failure point). This analysis identifies several previously unrecognized failure modes, including two additional double-failure points. As expected, no additional single-failure points were found. This study also shows a greater dependence between the Primary Heat Transport System (PHTS) and the Direct Heat Removal System (DHRS) than previous studies of the SHRS have indicated.