Reliability analysis of the scram system of the Missouri University research reactor

The reliability analysis of anticipated transients without scram is a topic of considerable significance in reactor safety studies. The article describes the results of a recently completed study on the reliability of the Missouri University Research Reactor (MURR) scram system. For this reactor it has been determined that the failure to initiate a scram automatically or manually within 7.5 sec of an isolation-valve closure can lead to core meltdown. Since valve closure is a credible accident (it has occurred once during the past 5 years), it is important to know the reliability of the scram system. The authors have used the event and fault-tree methodologies to analyze accident sequences and the scram system. Several common-mode failures have been identified, and the availability probabilities for each primary event were obtained by a detailed examination of the MURR operating records. Detailed analysis shows that the MURR scram system is highly reliable.