Accident Progression for a Loss-of-Heat-Sink with Scram in a Liquid-Metal Fast Breeder Reactor

An analysis of a slow core meltdown in a liquid-metal fast breeder reactor was performed for the conditions of loss-of-heat-sink following neutronic shutdown. Simple models were developed for the prediction of phase changes and/or relocation of the core materials, including fuel, coolant, cladding, ducts, control rod absorber material (B₄C), and plenum gases. The sequence of events was accounted for, and the accident progression was described up to the point of recriticality. The neutronic behavior of the disrupted core was analyzed in r-z geometry with a static transport theory code (TWOTRAN). For most scenarios assessed, the reactor is expected to become recritical, although large ramp rates are not anticipated.