SIMPLIFIED METHODOLOGY FOR ESTIMATING IMPACT ON RISK DUE TO SOURCES OF UNCERTAINTY

摘要

In estimating the impact on risk for various sources of uncertainty, a pseudo-quantitative approach was hypothesized to determine a qualitative estimate of the impact on overall risk. Two components were used in assessing the Uncertainty Risk Impact (URI) index. First, the importance measure of the associated plant system or initiating event, e.g., Fussell-Vesely value, was used to determine the contribution to CDF or LERF, whichever proved more relevant. Three bins were defined based on the quantitative contribution, i.e., low being < 1%, medium being 1 to 10%, and high being 10 to 100%. Then, an estimate of the degree of uncertainty was the other component used to help determine the impact on risk, which involved qualitatively assessing the degree of how uncertain a specific issue may be, i.e., low, medium, or high. Using a matrix for these two components, the intersection of the degree of uncertainty with the estimated contribution to CDF or LERF yielded an index for the URI, such as low, moderate, or high. The benefit of this simplified methodology revealed that without spending a significant amount of effort, the PRA analyst can easily identify what uncertainties are most important to overall risk by comparing both their degree of uncertainty and associated elemental contribution to risk.