Use of Fuel Assembly/Backfill Gas Effective Thermal Conductivities to Predict Basket and Fuel Cladding Temperatures Within a Rail Package During Normal Transport

Two-dimensional finite element thermal simulations of large rail casks designed to transport spent nuclear fuel assemblies were performed for normal conditions. Two different effective thermal conductivity models, developed by other investigators, were implemented within the basket openings that support the fuel assemblies. The effective thermal conductivity models affect the peak cladding temperature directly by influencing the temperature difference between the hottest cladding at the cask center and the walls that surround it. It also affects it indirectly by influencing the center basket wall temperature. The fuel assembly heat generation rates that cause the peak cladding temperature to reach the allowed limit were determined for both effective thermal conductivity models. At those generation rates the basket wall temperatures in the periphery of the package were highly nonuniform. The basket wall temperatures determined in this work will be used in future studies to develop improved thermal models of fuel assemblies.