Use of influence diagrams for evaluation of severe accident management strategies

This paper presents a new approach for developing and assessing severe accident management strategies under uncertainty in nuclear power plants. The strategy of flooding the reactor cavity during the TMLB' sequence as a means to prevent vessel breach is used as an example. The modeling of complex decision problems, such as those encountered in severe accident management, involves a large number of random variables. While the state of the art relies on decision trees, influence diagrams have been proposed as an alternative. Large decision trees cannot be displayed except in pieces, but influence diagrams (as suggested in this paper) can depict much larger and more complicated models, such as those required for the development of strategies for managing severe accidents in nuclear power plants. The advantages of influence diagrams include a compact and unambiguous representation of probabilistic dependencies of various events or processes and good communication of the structure of a decision model. Furthermore, influence diagrams allow for the rapid identification of important variables and are easily modified in case the decision maker wants to add or remove some nodes or reverse arcs, making the influence diagrams good tools for developing, as well as evaluating, severe accident management strategies. The superiority of this model is clear in more complicated situations, such as multidecision problems