Importance Analyses on Phenomenological Parameters for the Aerosol Dynamics Models in I-COSTA for a Severe Nuclear Power Plant Accident

In this study, using in-house code I-COSTA, importance analyses are performed on the phenomenological parameters in the aerosol dynamics using International Standard Problem No. 44. The analyses consider twelve parameters used in multicomponent sectional equations and Mason equations. For the first step of the analysis, Latin hypercube sampling is performed for the aforementioned parameters, and the number of samplings is determined using a comparison of averages and standard deviations between those samplings and the ones gathered from continuous distributions of the parameters. Sensitivity analyses are then performed on the airborne concentrations of the aerosol particles using I-COSTA, and the results are used to obtain the correlation coefficients between the parameters and the airborne concentrations. From the analyses, the dynamic shape factor, which accounts for the drag force of the non-spherical aerosol particles, is found to be one of the most important parameters in the aerosol dynamics. The saturation ratio in the Mason equation is also found to be an important parameter for aerosol particles with high solubility since the mass of the aforementioned particles is sensitive to the hygroscopic growth rate.