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

•Droplet heat transfer model is extended with new features and coupled in Lagrangian approach for droplet-tracking in containment atmosphere.•Model validations against single droplet experiments show good agreements on droplet motion and condensation/evaporation.•The higher gas temperature is, the more significant it reduces the droplet evaporation heat transfer.•Solute effect is significant for the small droplet evaporating and the dry aerosol growth, which dominates the droplet equilibrium diameter. 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 (