CHARACTERISTICS OF DEBRIS FROM SIMULATED MOLTEN FUEL COOLANT INTERACTION EXPERIMENTS

Studies on Molten Fuel Coolant Interaction (MFCI) resulting from a hypothetical core melt accident in Sodium cooled Fast Reactor is important as the MFCI phenomena is associated with generation of dynamic pressure which has a potential for mechanical damage to the reactor vessel and structures. During MFCI, molten core at high temperature interacts with relatively cooler liquid sodium and undergoes fragmentation. The size, shape and physical state of debris depend on the associated fragmentation mechanism, super heat of the melt and sodium temperature. The fragmented particles settle on core catcher and form as debris bed, which continue to generate decay heat. Characteristics of debris govern the debris bed coolability and needs thorough investigation. Experiments have been conducted by releasing a high temperature melt at 2400 degrees C into liquid sodium at 400 degrees C to study the fragmentation phenomena. Molten mixture of alumina and Iron generated by aluminothermy process was used for simulating the corium. After the experiment, sodium was drained and debris was retrieved by vacuum evaporation method. Size distribution and mass median diameters of the resultant debris was determined by sieve analysis. The debris was segregated into metallic/nonmetallic particles using magnetic separation method and subjected to microscopic investigation for obtaining morphological characteristics. This paper outlines about the characteristics of debris generated by interaction of simulated corium with sodium towards assessment of fragmentation mechanism and associated debris coolability.