Parameter and model uncertainty analysis using dempster-shafer theory in nuclear probabilistic risk assessment

Abstract : In Nuclear Power Plants, Probabilistic Risk Assessment (PRA) insights contribute to achieve a safe design and operation. In this context, decision making process must be robust and uncertainties must be taken into account and controlled. In the current PRA practice, the model uncertainty due to different alternative assumptions made in logical structures of event or fault trees may be neglected or addressed only through sensibility studies. In this paper, two approaches for dealing with the model uncertainty: the weighted mixing approach and the enveloping approach will be presented in the Dempster-Shafer Theory framework which is used to take account of parameter uncertainty at the same time. The weighted mixing approach is recognized to be suitable only to cases where the experts have sufficient information to express their degrees of belief in terms of probabilities with regard to alternative models. On the contrary, the enveloping approach will be more appropriate to apply when no information is available. This approach will be illustrated through a practical example in the context of level 1 PRA application at EDF.