Fuel-Coolant Interaction Test Results Under Different Cavity Conditions

Some advanced reactors adapt the in-vessel corium retention concept by cooing the outside wall of the reactor vessel in severe accidents. If a reactor vessel failure happens in this case, the molten corium in the reactor vessel is directly injected into the water in the reactor cavity without the process of a free fall. Experiments using ZrO₂ and molten corium to simulate the conditions in which the reactor vessel is fully flooded were recently carried out at the Test for Real cOrium Interaction with water (TROI) experimental facility, and the results are compared with the data produced under conditions in which the reactor vessel is partially flooded. It was observed that the melt front velocity in the water under submerged reactor conditions is much faster than that under partially flooded reactor cavity conditions, and a large bubble was observed at the surface of the mixing zone under submerged reactor conditions. Accordingly, it is estimated that the breakup of the melt jet in the water during the fuel-coolant interaction (FCI) test under submerged reactor conditions would be different than that of the FCI test under partially flooded reactor cavity conditions.