Molten stainless steel at ∼1720°C and melts of iron and alumina or 54 wt% UO2, 16 wt% ZrO2, and 30 wt% stainless steel at 2400 to 2800°C were poured onto 0.95- to 7.62-cm-thick steel structures. The melts rapidly penetrated these structures, probably by a thermal ablation process. Coatings of 0.2- to 2-mm-thick urania on the surfaces of the steel delayed penetration by the very high-temperature melts. Data from tests involving melts impinging on steel structures could be correlated by the single-parameter, empirical expression A finite difference model of the experiments is described. The model is used as the basis for predicting the extent of crust formation when melts contact cold steel and to suggest that a gas gap may form between the steel and any crust of frozen material that does form.