On the distribution type of uncertain inputs for probabilistic assessment

The effect of distribution type of uncertain inputs on the probabilistic assessment result of a system is illustrated. The tested systems include linear function, positive exponential function, negative exponential function, and reciprocal function, and a proposed corrosion mechanism for radwaste package in addition. The four types of distributions analyzed are uniform (U), log-uniform (LU), normal (N), and log-normal (LN) distributions. Latin hypercube sampling (LHS) was applied to take samples from the uncertain inputs, and the data sets obtained from the said samples were uncorrelatedly arranged before computation. The Fourier amplitude sensitivity test (FAST) was also applied to calculate the sensitivity index of the four distributions. Based on the safety assessment point of view, the results of this paper provide a rationale for the choice of the distribution type between U and LU distributions when the available data points are scarce. The result of the FAST indicates that the sensitivity of the four distributions is, in the order, SU>SLU>SN>SLN. This suggests a need to carefully identify whether the uncertain inputs are of U distribution for the purpose of sensitivity analysis.