Comparative Uncertainty Analysis of the Phenomenological Parameters in Severe Accident Source Term

Abstract

Regulatory agencies require emergency preparedness for possible radioactive release severe accidents, after the Chernobyl and Fukushima accidents. Radioactive source term is a characterization of possible radioactive releases including timing and magnitude of the radioactive materials. Due to difficulties in performing experiments for the nuclear severe accidents in real-world conditions, source term can only be predicted using simulation codes, such as MAAP, that integrate various phenomenological models from smaller-scale experiments. Considerable efforts have been taken to realistically estimate the source term during severe nuclear reactor accidents, but uncertainties exist in using the integrated models. Therefore, uncertainty analyses must accompany the source term predictions.

The purpose of this research is to identify the sets of MAAP4 phenomenological model parameter coefficients with great influences on the source term overall uncertainty. The identified parameters with great influences on the overall uncertainty are compared for different accident scenarios and plant configurations. If some model parameters are influential regardless of the accident scenario or the plant configuration, the overall source term uncertainty may be reduced by focusing on reducing uncertainties on the corresponding models. Achieving higher level of prediction through uncertainty reduction within the integrated severe accident codes may help the industry by allowing the utilities to meet the boundaries of regulatory policies with reduction in costs without compromising the apparent safety to the public and to the environment. Although this research is focused on an unmitigated station blackout and an interfacing systems loss-of-coolant accidents, the approach used is expected to be applied for wider range of accident scenarios and plant configurations in the future studies.