The Effect of the UO2/ZrO2 Composition on Fuel/Coolant Interaction

A series of experiments on fuel/coolant interaction (FCI) was performed in the TROI facility, where the composition of the mixture was varied. The compositions of the UO2 and ZrO2 mixture in weight percent were 50:50, 70:30, 80:20, and pure ZrO2. The responses of the system including the temperature of the pool of water in the test vessel, pressure and temperature of the containment vessel, and dynamic pressures and force were measured. In addition, high-speed movies were taken through the windows. The tests using corium with a 70:30 composition and pure zirconia resulted in a spontaneous energetic steam explosion, while the tests with other compositions did not lead to an energetic FCI. The debris size distribution and pressure and temperature responses clearly indicated the cases with an energetic explosion and the cases without an explosion. The highspeed movie taken during the FCI through the visible window clearly disclosed the outstanding phases of the FCI, which were the melt entry phase, the triggering phase, and the continued melt jet and expansion of the mixing zone phase.