A Study of Fuel Removal via Inner Blanket Intersubassembly Gaps During the Disruption Phase of Hypothetical Loss of Flow Accidents in Heterogeneous LMFBR Cores

The potential for fuel removal through the inner blanket intersubassembly gaps before the formation of interconnected pools of fuel and steel has been investigated for the Clinch River Breeder Reactor heterogeneous core under conditions of an unprotected loss of flow accident. The relevant physical phenomena were simulated with the SIMMER-II accident analysis code with the necessary model adaptations identified. A base case has only been set up for the four inner sub-assembly rings. Based on the understanding gained from this case and an evaluation of a sensitivity study, combined variations for an enhancement of fuel removal are examined. For low flow resistance in the gap, sustained pressurization in the driver assemblies, and delayed blanket gap wall failure, a substantial amount of fuel can be removed from the active core through the inner blanket gaps. The analyzed problem is closely related to the thermal propagation issue.