Uncertainty Analysis Plus Importance in Severe Accident Calculations: Quantitative Evaluation of Important Parameters

This paper describes a systematic framework for quantifying the degree of contribution of each parameter to the uncertainty of the output in severe accident assessment. This research is an extension of the recent work of the authors on uncertainty assessment of severe accident calculations where the main sources of uncertainty are identified through the so-called modified PIRT approach. The proposed methodology here utilizes uncertainty importance measures for the quantification of the effect of each input parameter on the output uncertainty. A response surface fitting approach is proposed for estimating the associated uncertainties with less calculation cost. The quantitative results are used to plan in reducing epistemic uncertainty in the input variable(s). The application of the proposed methodology is demonstrated for the ACRR MP-2 severe accident test facility.