[en] Some postulated accident scenarios lead to a picture with most of the fuel and some structural steel sealed inside the original core volume by frozen plugs at the original core entrance and exit. eventually the fuel will either melt out or blow out of such a sealed volume but in the interim between plug formation and eventual dispersion the question remains How will the fuel distribute inside the bottled core. Fuel motion is primarily determined by the generation, movement and final recondensation of fuel and steel vapor. When the vapor is generated at a very rapid rate, large amplitude pressure waves are formed. To aid in the analysis of such conditions, an experimental program has been set up to study the behavior of a two-phase mixture during the passage of a shock wave