Petri Net Modeling for Probabilistic Safety Assessment and its Application in the Air Lock System of a CANDU Nuclear Power Plant

Historically, fault trees are extensively used in Probabilistic Safety Assessment (PSA) to model and evaluate the probability and consequence of failures of complex engineering systems, such as nuclear power plants. Scenarios of hypothetical accidents resulting in severe core damage can be developed. Petri net is another modeling technique that offers many advantages when comparing with fault trees, such as is ability to represent the time sequence of the events along with their duration. In this research, Petri net theory is extended to model system failures. The transformations required to model logic gates by Petri nets are explored and examples provided. Methods for qualitative analysis for Petri nets are presented. The application of Petri net in the airlock system of a Canada Deuterium Uranium (CANDU) reactor is explored. It is further demonstrated that Petri net can be used in both coherent and non-coherent systems.