Two steam explosion experiments were performed in the TROI (Test for Real cOrium Interaction with water) facility by using partially oxidized molten corium (core material), which is produced during a postulated core melt accident in a nuclear reactor. A triggered steam explosion occurred in one case, but none occurred in the other case. The dynamic pressure and the dynamic load measured in the former experiment show a stronger explosion than those performed previously with oxidic corium. Meanwhile, a steam explosion is prohibited when the melt temperature is low, because the melt is easily solidified to prevent a liquid-liquid interaction. The partially oxidized corium could enhance the strength of a steam explosion due to the thermal energy from an exothermic chemical reaction between the water and the uranium metal with a sufficient superheat extracted during melting. The melt composition effect on a steam explosion load, which was not included during the nuclear design, needs to be included in it.

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The suppression of a vapor explosion is reviewed from a void fraction point of view from previous research results and the results of an experiment and analysis for TROI using a prototypic reactor material. In a tin-water system, a high fraction of air which played the role of a steam reduced the peak pressure of a steam explosion. According to the sensitivity analysis that was carried out with an increase in the vapor volume fraction, an energetic vapor explosion hardly took place in the mixture with a high void fraction. In higher vapor fraction conditions (αv> 0.3), the vapor explosion was very weak. A prototypic corium shows a relatively high void fraction compared to the ZrO2 which is known as an explosive material because the corium system generated many smaller particles compared to the ZrO2 system. The corium system shows a relatively low explosivity compared to the ZrO2 system because the high void fraction of the corium system plays the role of preventing a contact between the water and the hot melt drops in the triggering stage. When considering the experimental results for the role of air instead of steam, an air supply system to provide a high volume fraction during a premixing process can radically prevent and/or mitigate a steam explosion.