small particles solidify faster than larger ones. Furthermore, the models for instability growth at interfaces between flowing media (e.g. Kelvin-Helmholtz, Rayleigh-Taylor, Conte-Miles, ...) show a correlation between particle size after fragmentation and the ratio of the density of the fragmenting medium (water-vapor mixture) to the density of the fragmented medium, which can also be demonstrated experimentally. In the case of corium (density of ~ 8000 kg/m³), much smaller droplets (~ 3 - 4 mm) result than when alumina (Al2O3) is used as a corium simulant with a density of just under half that of corium with droplet sizes in the range of 1 - 2 cm. Jet fragmentation experiments conducted at JRC ISPRA under typical reactor conditions with masses of molten corium up to 200 kg and melt jet diameters of 5 - 10 cm in diameter in pools of saturated water up to 2 m deep resulted in success with respect to steam explosions only when Al2O3 was used as the corium simulant. Despite various efforts on the part of the experimenters, it was never possible to trigger a steam explosion in the corium experiments in FARO.(Will be continued ...) In these events the passage of the pressure wave through the predispersed material creates flow forces which further fragment the melt, resulting in rapid heat transfer, and thus sustaining the wave. Much of the physical destruction in the Chernobyl disaster, a graphite-moderated, light-water-cooled RBMK-1000 reactor, is thought to have been due to such a steam explosion. In a nuclear meltdown, the most severe outcome of a steam explosion is early containment building failure. Two possibilities are the ejection at high pressure of molten fuel into the containment, causing rapid heating; or an in-vessel steam explosion causing ejection of a missile (such as the upper head) into, and through, the containment. Less dramatic but still significant is that the molten mass of fuel and reactor core melts through the floor of the reactor building and reaches ground water; a steam explosion might occur, but the debris would probably be contained, and would in fact, being dispersed, probably be more easily cooled. See WASH-1400 for details. Steam explosions are often encountered where hot lava meets sea water or ice. Such an occurrence is also called a littoral explosion. A dangerous steam explosion can also be created when liquid water or ice encounters hot, molten metal. As the water explodes into steam,