[en] Under prompt burst conditions the work potential of expanding fuel vapor is a sensitive function of the ability of fission product gases to cause fuel dispersal milliseconds before dispersal would occur from fuel vapor pressure alone. This relation is of potentially significant importance and merits investigation. A fuel disruption experiment at Sandia Laboratories exhibited rapid disruption probably below but near the fuel melt temperature. The fuel was being heated at 130K/msec when vigorous dispersal occurred in the hottest regions near the fuel melting point. Fuel vapor could not have been responsible. Dispersal is attributed to rapid release of fission product gases under the prompt burst conditions. Further tests are planned to explore this important phenomenon