Liquid immiscibility in a (O,U,Zr) model corium

New data on the miscibility gap in the liquid state in both O-U and O-U-Zr phase diagrams are reported. Mixtures are melted by electron bombardment. Tie-lines are determined in the O-U miscibility gap at 3090 K as well as in the O-U-Zr ternary system at 3223 K. 'Metallic' and 'oxide' liquids are immiscible in a large range of temperature and composition in both systems. The miscibility gap extent is extrapolated by thermodynamic calculations. The quenched microstructures of the different liquid phases are described and interpreted using a solidification path calculation. For the (O,U,Zr) alloys entering the miscibility gap, the minor oxide liquid phase is in the form of droplets in the metallic parent liquid. The droplets seem to segregate at the ingot surface. This leads to a layer formation in the case of the O-U system where there is the greatest difference between the two liquid compositions. (orig.)