Methods for the estimation of confidence bounds for the top-event unavailability of fault trees

The estimation of confidence bounds for the probability of existence of the top event of a fault tree is the subject of this work. Given the uncertainties of the primary input data a method is described for the evaluation of the first two moments of the top event existence probability. These moments are then used to estimate confidence bounds by several approaches which are based on standard inequalities (e.g. Tchebycheff, Cantelli, etc.) or on empirical distributions (the Johnson family). Several examples indicate that the Johnson family of distributions yields results which are in good agreement with those produced by Monte Carlo simulation. (Auth.)