[en] The purpose of research described in this paper is to begin to develop an understanding of the coarse-mixing behavior of jets of molten fuel falling through water. This knowledge will also be used in the development and assessment of the Integrated Fuel-Coolant Interactions (IFCI) computer code being developed at Sandia National Laboratories. Sandia's jet-mixing program currently consists of four series of experiments addressing the important issues of liquid-jet mixing. These four series are (1) jets of molten iron/alumina falling through air; (2) jets of water falling through air; (3) jets of molten iron/alumina falling through water (referred to as boiling-jet experiments); and (4) isothermal jets falling through water. This paper describes the results of the boiling (EJET) and isothermal (IJET) series, since these results are most applicable to reactor-safety issues