Melt expulsion and direct containment heating in realistic plant geometries

High pressure ejection of melt from the RPV may potentially occur in a large fraction of core melt accidents. Scaled tests show nearly complete dispersal of debris from the cavity. The test results presented indicate that simple structures may not greatly mitigate the dispersal of debris into the containment region. Interactions with walls and piping appear to be dominated by the melt splashing from the surface and subsequently being reentrained into the gas stream. Near the cavity exit, debris retention by crust formation on surfaces may be insignificant because the freezing rate is small compared to the flow of molten material. The results from the HIPS-8C experiment show that debris removal from the cavity via the annular gap around the RPV is by entrainment of melt particles after the onset of gas discharge from the pressure vessel. Jet deflection and splashout do not significantly contribute to debris dispersal from this region. These results imply that the quantity of melt entering the containment dome from around the RPV is proportional to the flow area of the annular gap. Aerosol measurements indicate a bimodal size distribution with contributions by vapor condensation and mechanical fragmentation. Estimates of the quantity of melt aerosolized in the experiments range from 0.3 to 5.2 percent of the mass of melt dispersed