Single droplet vapor explosion experiments

In a postulated severe accident in a light water reactor, molten fuel may contact a pool of coolant either in-vessel or ex-vessel. This contact may become an explosive interaction testing the mechanical strength of the reactor vessel and/or the containment building. When a vapor explosion occurs, hot material rapidly fragments resulting in a dramatic increase in the fuel surface area and hence the heat transfer rate. Since a single droplet explosion is considered to be a unit cell of the intermediate or large scale vapor explosion, many past researchers have used this small scale experiment to investigate the vapor explosion triggering behavior and its possible fragmentation mechanism. Some initial conditions for these past experiments are summarized. In most cases water was used as a coolant material. A number of metal or metal oxides were used as simulant fuels, e.g., lead, tin, bismuth, iron-oxides and UO/sub 2/. In this paper the authors describe the baseline experimental results in which iron-oxide droplets of about 75 mg at 19000C are injected into a large water pool of about 4 kg at 150C. They also discuss scoping experiments in which mass of the iron-oxide droplets and viscosity of the coolant were varied