AbstractA model for small-scale single droplet fuel/coolant interactions (FCIs) is proposed, which considers the growth of a coolant vapor/liquid interfacial disturbance into a coolant liquid jet during the collapse of the vapor film surrounding the fuel. This results in the encapsulation of the jet as coolant drops beneath the fuel surface and leads to fragmentation of the fuel. In this model, the FCI process is divided into four stages: film boiling around a molten fuel droplet in an infinite coolant pool, film collapse and coolant jet formation, coolant jet penetration and entrapment in the fuel, and rapid evaporation of entrained coolant and fragmentation of the fuel. The process repeats itself cyclically from the second stage. For the single-droplet experiments performed previously, the model predicts the qualitative trends of steam bubble growth and collapse, the final size of fuel fragments, and time scale for the fuel fragmentation.