Fault-tree analysis of the EBR-II reactor shutdown system

As part of level I Probabilistic Risk Assessment (PRA) of the Experimental Breeder Reactor II (EBR-II), detailed fault trees for the reactor shutdown system are developed. Two classes of transient events that are of particular importance to EBR-II operation and require reactor shutdown are loss of flow (LOF) and transient over power (TOP). Normally in these events, detection channels would automatically open a number of contacts in two redundant shutdown strings. The paper gives the probabilities of scram failure in case of an LOF or TOP. Fault-tree analysis of the EBR-II shutdown system has provided not only a systematic process for calculating the probabilities of system failures but also a useful means for understanding the system and how its components interact during transient events that require shutdown