Thermal Hydraulic Analysis of In-Vessel Core Catcher of a Pool Type Fast Breeder Reactor

ABSTRACT

Core melt down scenario in a Fast Breeder Reactor (FBR) results in thermal interaction of hot molten core with cold liquid sodium and generate fragmented debris. Accumulation of these core debris on to the main vessel bottom result in breaching of main vessel (MV) due to inadequate removal of the decay heat generated from the core debris. Hence as defense-in-depth, an in-vessel Core Catcher (CC) system is provided in FBR just below the strong back of the core support structure to collect, support and maintain the debris in coolable and sub-critical configuration. Heat generated by the debris settled on CC is removed by natural convection so that main vessel temperature does not exceed the allowable value.

The geometry considered in the present study for natural convection is a 2-D axi-symmetric enclosure with an internal heat source of 1 MW. Flow fields and isotherms are obtained for the computational domain to assess the heat removal capability of the core catcher and main vessel bottom temperature for certain perceived scenarios after the core melt accident. The main focus of analysis is to study the effect of possible geometrical variations in gaps between the bottom plate of core catcher and main vessel. The gap is varied from 25 mm to 100 mm. The change in main vessel temperature is found to be ˜2 K which can be considered as insignificant.

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