AbstractDuring a severe nuclear plant accident, molten fuel can contact water in the core region, the lower plenum, or in the cavity below the reactor vessel. The interactions that take place can vary from benign boiling to explosive vaporization. If the fuel contains a metallic component, rapid oxidation of the metal can occur during the fuel/coolant interaction (FCI). The hydrogen generated from this reaction can increase the threat to containment integrity.Experiments have been conducted with 10 to 20 kg of two kinds of thermite-generated molten fuel simulants: corium and iron-aluminum oxide. Both saturated and subcooled water were employed as coolants. Explosive and nonexplosive FCIs were observed. Up to 30% of the metal was reacted in some cases. For some of the tests, the extent of reaction appeared to depend more on the water subcooling than on the degree of fragmentation as measured by posttest sieving. Models of hydrogen generation are proposed and compared to a broad range of experiments. Predictions agree qualitatively with many of the experimental observations. A more accurate model of hydrogen generation would have to be coupled to a dynamic thermal-hydraulic calculation of the important phases of an FCI: coarse mixing, fine fragmentation, explosion propagation, and vapor expansion.