Modeling of Neutronics and Thermal-Hydraulic Aspects During Total Instantaneous Blockage of Central Fuel Subassembly in a Fast Reactor

Total instantaneous blockage (TIB) at the inlet of a subassembly (SA) of a Sodium cooled Fast Reactor(SFR) is a beyond design basis event and a theoretical envelope of all small blockages. This study aims to conduct a coupled thermal hydraulics and neutronics analysis of TIB in a medium sized SFR. Towards this, a coupled thermal hydraulics and neutronics model is developed by solving heat transfer equations and point kinetics equations numerically. TIB analyses using the developed model predicted the time of occurrence of key events. TIB is detected earlier than predicted by a previous study which does not consider reactor power change during the transient. The rise in the sodium outlet temperature beyond the threshold level for detection is observed for all the fuel SA before the end of fuel melting in the blocked SA. Thus, assurance towards early detection of TIB by core temperature monitoring system is strengthened