An evaluation of fission product release rates during debris dispersal

Failure of a reactor pressure vessel under severe accident conditions could result in debris dispersal into the containment if the vessel were at an elevated pressure. This process could influence both containment loading and fission product release from the core debris. Recent modeling approaches have focused on the potential for debris entrainment by high velocity gases resulting from the primary system blowdown. This paper considers both the potential for entrainment, which also results in deceleration of the gas flow as the entrained debris is accelerated, and the simultaneous potential for displacing debris from the reactor cavity without fine scale particulation. If substantial amounts of the debris would be expelled from the cavity region as a relatively continuous mass, limited amounts would be dispersed into the containment atmosphere, and the interfacial area available for heating of the containment atmosphere and for release of fission products from the melt would be minimal. The resulting model is compared with the recent direct containment heating experiments, including those incorporating fission product simulants