THERMAL EVALUATION OF LOADING AND DRYING OPERATIONS OF A HIGH CAPACITY SPENT FUEL STORAGE CANISTER

Higher capacity designs for storage of spent fuel provide an advantage of ALARA during loading operations and optimal use of space on the storage location. In this paper the thermal analyses for a transfer system to store 87 BWR fuel assemblies are presented. The assemblies are stored in a welded canister whose fuel assembly’s positions are maintained by a non-welded basket configuration. The operations to complete the drying operations and to move the canister with in the plant employs a shielded transfer cask which also uses a cooling system to remove heat from the system. Heat rejection internal to the canister is primarily accomplished by natural convection, and heat rejection from the canister surface uses circulating water. Two separate thermal analysis models are employed for this evaluation. During the drying phase, a detailed three-dimensional model of the basket and canister determines the transient thermal response of the fuel. This defines the duration of the vacuum drying cycle. Segments of the operation permit the helium backfill in the canister to reject heat by convection from the fuel assembly to the canister surface. This is simulated using a two-dimensional CFD model which incorporates porous media modeling to represent the hydraulic resistance of the fuel rods and fuel assembly grids. Certain transient conditions require the results of the three-dimensional conduction model to define the initial conditions of the two-dimensional CFD transient model. The simulation methodology makes efficient use of both technologies to determine the thermal response of the system for all operational conditions. The results confirm that the maximum component temperatures remain within their allowable temperatures.