Extension of droplet/aerosol heat transfer model coupling Lagrangian approach in containment atmosphere under severe accident

Abstract

Spray droplet dynamics are expected to significantly affect steam condensation, droplet evaporation, and global gas mixing in the containment atmosphere. During severe accidents, droplets may evaporate under high gas temperatures (>200 °C) such as hydrogen fire radiation, and water-soluble aerosols such as CsI and CsHO may dissolve in droplets. An extension of the droplet heat transfer model was conducted to account for these conditions and coupled with a Lagrangian approach for droplet tracking. The approach was comprehensively validated through single droplet experiments, demonstrating the feasibility of this new approach. Analyses of the effects of high atmosphere temperature, droplet curvature, and aerosol solute indicate that, 1) High gas temperature significantly reduces heat transfer, with the effect increasing at higher gas temperatures; 2) Droplet curvature enhances droplet evaporation, but this effect is limited to tiny droplets (<100 nm) compared to other effects; 3) The solute effect significantly impacts small droplet evaporation and dry aerosol growth, dominating the final equilibrium droplet diameter. The extended droplet/aerosol heat transfer model fills a gap in the knowledge of containment spray under severe accidents. A feasible way to approximate the minimum spray droplet size in the heat transfer model is to truncate or initialize the small droplet by the equilibrium diameter.