Combining dynamic fault trees and event trees for probabilistic risk assessment

As system analysis methodologies, both event tree analysis (ETA) and fault tree analysis (FTA) are used in probabilistic risk assessment (PRA), especially in identifying system interrelationships due to shared events. Although there are differences between them, ETA and FTA, are so closely linked that fault trees (FT) are often used to quantify system events that are part of event tree (ET) sequences (J.D. Andrew et al., 2000). The logical processes employed to evaluate ET sequences and quantify the consequences are the same as those used in FTA. Although much work has been done to combine FT and ET, traditional methods only concentrate on combining static fault trees (SFT) and ET. Our main concern is considering how to combine dynamic fault trees (DFT) and ET. We proposed a reasonable approach in this paper, which is illustrated through a hypothetical example. Because of the complexity of dynamic systems, including the huge size and complicated dependencies, there may exist contradictions among different dynamic subsystems. The key benefit of our approach is that we avoid the generation of such contradictions in our model. Another benefit is that efficiency may be improved through modularization.