Thermal Analysis of Irradiated Fuel Subassemblies and Fuel Pins During Storage in Concrete Pits of Head-End Facility

Irradiated fuel subassembly (SA)/fuel pins, with significant decay heat are transported from reactor and stored in hot cells (HCs) before reprocessing. During transportation they are heavily shielded and no forced cooling is provided. The HCs are made of concrete structures, the outer surfaces of which are force cooled. During these processes, the fuel pin clad temperature and concrete temperatures are to be limited within specific safety limits. These temperatures are function of the decay power and geometric details of surrounding structures. To predict these temperatures, three-dimensional conjugate conduction–convection–radiation heat transfer analysis has been carried out. For this purpose, the computational fluid dynamics (CFD) code STAR-CD has been utilized, wherein individual fuel pins, steel cans, hexagonal wrapper, lead shielding blocks, and concrete structures have been considered in detail. Based on parametric studies pertaining to fuel pin transportation, it is established that for a decay power of 150 W, natural convection is adequate with maximum clad temperature of 686 K. From the studies related to storage in HCs, it is seen that nine fast breeder test reactor (FBTR) SA can stored in hot cell-1 (HC-1), with a decay power of 31.3 W per SA, to respect the temperature limits. For 3 prototype fast breeder reactor (PFBR) cans and 2 FBTR cans stored in hot cell-3 (HC-3), a decay power of 12.5 W per FBTR can and 44 W per PFBR can, can be handled without exceeding temperature limits.