Visual Observation of Ultra-fast Heat Transfer Behavior on Base-triggered Vapor Explosion

Spontaneous vapor explosion can occur when a layer of the high temperature molten material lies on the water pool or on the moisture floor. This is so-called base-triggered vapor explosion. The base-triggered vapor explosion is supposed to occur in the case of a severe accident in various facilities. It is very important to clarify the base-triggered vapor explosion from the viewpoints of the prediction and the prevention of the vapor explosion. In order to evaluate the behavior of the base-triggered vapor explosion, the experimental apparatus is designed and constructed. The experiments using U-Alloy95 as a simulating substance are conducted. Consequently, the behavior of the molten material can be observed in detail with this experimental apparatus. The behavior of the molten material at the vapor explosion is evaluated by image analysis. Based on the analysis results, conversion ratio, which is defined as ratio of the kinetic energy at the vapor explosion to the initial thermal energy, is evaluated.