Insights on the sensitivity and uncertainty in the risk of core damage from a typical BWR-5 plant

This paper presents some of the insights obtained from a study of the uncertainty and sensitivity in the core damage risk from the operation of a BWR-5 plant. The results of the efforts to evaluate some of the sensitivities in the plant design, the impacts of plant modifications, and the importance of uncertainties in the plant data have shown that the problems of manipulating large amounts of risk data in an accessible format are now tractable. Event tree models provide the framework for the BWR-5 risk evaluation. These models were structured to meet the following objectives: provide a macro-level risk model that could be used as the basis for estimating plant risk measure sensitivities and uncertainties, and that could be enhanced with more detailed risk data and models; provide a basis for deriving some initial insights on the system level effects that are apparent for the plant, and for the preliminary identification of the important risk contributors; and provide a structure for implementing the various methodologies used for sensitivity and uncertainty analysis to gain a better understanding of the comparative techniques. The sensitivity and uncertainty results of this study provide a unique perspective on the way in which risk parameters are affected by changes in plant design or operation, analytic assumptions, and limitations in the data base