An alternative fragmentation theory for a melt droplet and visual data analysis of the large-scale steam explosions

Abstract

An alternative fragmentation theory has been suggested for the steam explosion phenomenon. Under the conditions of the large-scale steam explosion experiments previously done by the members of Japan Atomic Energy Research Institute, model conservation equations have been solved and the maximum heat transfer coefficient is calculated as . Using this heat transfer coefficient, expansion velocity of the steam water interface has been calculated as about 1800 m/s. It was demonstrated that this interface velocity as a result of local explosive steam production is high enough to obtain a shock wave, which is necessary to have a large-scale steam explosion. To have an overall understanding about the whole steam explosion process and the relation among its stages, above mentioned data have been examined and evaluated in detail. Using the debris size distribution regarding to this data, it has been found out that surface area enlargement of the melt fragments for an experiment resulted in explosion is about seven times greater than that for a no-explosion experiment done using the same amount of melt and water. Qualitative examination of the visual data revealed that steam production per unit time during an explosion is thousands of times greater than that in the case of no-explosion. Therefore, only area enlargement cannot explain the huge amount of heat transfer. Another approach, as suggested in the present work, which considers the relative velocities of the melt and the coolant, should be considered.