An application of the ESD framework to the probabilistic risk assessment of dynamic systems

Dynamic reliability is the probabilistic study of man-machine-software systems affected by an underlying physical process. The theory of probabilistic dynamics [1] established that dynamic reliability methodologies are essentially semi-Markovian frameworks and can be expressed by an extension of the Chapman-Kolmogorov equation. The mathematical complexity associated with the assessment of dynamic systems' behaviour can be rather overwhelming for real life size systems. This is due to the fact that dynamic methodologies emphasize a component based representation rather than the sequence based representation used in the traditional Event Tree/Fault Tree framework or in the original Event Sequence Diagram (ESD) Framework. An extension of the ESD framework was proposed that facilitates capture of dynamic situations. The modeling framework is composed of events, gates, conditions, competitions and constraints which express many of the dynamic situations encountered in the evolution of accidents [2]. The following paper illustrates an application of this extended ESD framework on a complex dynamic application. The problem at hand is an extension of a problem extensively studied in the validation of dynamic reliability algorithms, a simplified model of the fast reactor Europa [3]. A discussion on how ESDs can help in guiding dynamic reliability simulations as well as aggregating and binning the numerous scenarios generated by dynamic reliability algorithms is provided.