Linear stability analysis of a vapor film at melt jet-coolant interface

As a consequence of severe reactor accident, both in-vessel and ex-vessel pouring of melt jets into coolant pool below is possible. Breakup of these jets determines the further accident progression. Previous research was concentrated on in-vessel situation and available models of jet breakup were developed for film boiling conditions with thick vapor blanket. The present paper addresses the ex-vessel case which assumes relatively thin vapor films at jet surface. The existence of vapor layer with high viscosity at the jet-coolant interface may, under certain conditions, substantially change the flow instability features. The present work is aimed on adequate examination of the particular role played by viscous vapor film in jet fragmentation process. Analysis is based on the linear stability theory which allows to establish typical instability features. The criteria of change in fragmentation behavior are also found in the framework of proposed approach.