Study on Micro-Mechanism of 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 a nuclear reactor and in other industrial facilities. It is very important to clarify the occurrence condition and possibility of the base-triggered vapor explosion from the viewpoints of the prediction and the prevention of the vapor explosion. In order to evaluate the occurrence conditions and to clarify the micro-mechanism of the base-triggered vapor explosion, the experimental apparatus to observe the base-triggered vapor explosion from the bottom of the floor to above is designed and constructed. The experiments using U-Alloy95 as a simulant material are conducted. Consequently, the microscopic behavior at the interface between the molten material and water can be observed in detail with this experimental apparatus. The PIV analysis is conducted to the visual observation data obtained on the experiments in order to evaluate the overall behavior of molten material. The digital auto-correlation method is also applied to the visual observation data in order to evaluate the interfacial shape and the velocity distribution at the interface between the molten material and water. And blowout velocity of the molten material at vapor explosion is evaluated from the visual data obtained on the experiment. The generated pressure at the vapor explosion is estimated by using the blowout velocity. In addition, the experimental results are compared with the thermal interaction zone (TIZ) theory.Copyright © 2004 by ASME