In-Reactor Experiments on the Cooling of Fast Reactor Debris

First-of-a-kind fission-heated experiments utilizing uranium oxide particles in liquid sodium have been performed to assess the nature of the passive heat transfer between fast reactor fuel debris and overlying coolant. The experiments were designed to simulate the situation following a core disruptive accident in which molten core material is quenched, fragmented, and is dispersed as beds of decay-heated particulate within the reactor vessel. In two of the experiments, threshold dryout of the fuel particulate was produced. During several runs, dryout was maintained for long periods (approx. 1 h) with only modest temperature increases, demonstrating that while bed dryout may be a necessary condition for remelting of the fuel, it is not always a sufficient condition.