Consideration of Enhanced Safety based on CMR-concept for Large Fast Reactor

We have studied effectiveness of devices that inserts negative reactivity under both ULOF (Unprotected Loss of Coolant) and UTOP (Unprotected Transient Over Power) event of large fast reactor for enhancing safety. We investigated potential reactivity by replacing fuel subassembly with subassembly-type devices containing liquid fuel in tubes to enhance axial expansion reactivity feedback effect and to have "Controlled material Relocation; CMR" effect. Preliminary study indicated that the proposed liquid metal fuel device has possibility to shutdown both for UTOP and ULOF events by replacing 10-15% of fuel assemblies into the core, prior to melting fuels in driver core.