The analysis of metal- and oxide- fueled subassembly accidents in LMFBRs

A comparative subassembly accident analysis has been performed for liquid-metal fast breeder reactors with metal and oxide fuel elements, respectively. The study focused on local faults for design basis accidents, and a total instantaneous blockage for beyond design basis accidents. The results showed a larger margin to fuel melting in local faults, but a faster event progression in the total instantaneous blockage for the metal-fueled subassembly than for the oxide-fueled subassembly, mainly due to the high thermal conductivity and low fuel-steel eutectic temperature of the metallic fuel elements. However, a possibility was shown that a large fuel escape capability may reduce the failure propagation potential to neighboring subassemblies in the case of a metal-fueled subassembly. A possible mechanism and necessary conditions for the event termination were discussed. (author)