Insights from the recent steam explosion experiments in TROI

The paper discusses the results of steam explosion experiments of TROI-13, TROI-14, and TROI-15, which were performed under the research program named "Test for Real cOrium Interaction with water (TROI)." TROI-13 and TROI-14 used corium, which is a mixture of UO2 and ZrO2 at a 70:30 wt%, while TROI-15 used ZrO2. These three cases resulted in spontaneous steam explosions. It is an important observation from the aspect of the explosivity of prototypic material, as it was not observed in the previous experiments. Various aspects of the test results including cold crucible melting, hydrogen generation, melt temperature measurement, debris morphology, size distribution of the debris, dynamic pressure, dynamic force, shape of the melt jet, location of the trigger, response of the vessel pressure, and the response of the water pool temperature are discussed. The potential contributors to the explosivity of corium are suggested.