Use of Geometrically Accurate Fuel Models to Predict Cladding and Basket Temperatures Within a Truck Cask During Normal Transport

A two-dimensional finite volume mesh of a legal-weight truck cask cross section is constructed, including four pressurized water reactor fuel assemblies inside. Computational fluid dynamics (CFD) simulations calculate buoyancy-driven gas motion, natural convection and radiation heat transfer in geometrically accurate gas-filled fuel regions, and conduction within the solid components. Steady-state simulations are performed with the cask in a normal transportation environment for ranges of fuel heat generation rate and cladding emissivity, with atmospheric-pressure helium or nitrogen cover gases. The cask thermal dissipation capacity is defined as the fuel heat generation rate that brings the fuel cladding temperature to its allowed limit. That capacity is 23% higher when helium is the cover gas than for nitrogen. Increasing the cladding emissivity by 10% increases the capacity by 4% for nitrogen, but only 2% for helium. Stagnant-gas simulations using the geometrically accurate mesh predict essentially the same cask thermal dissipation capacity as simulations that include gas motion. This indicates that buoyancy-induced gas motion is not strong enough to significantly enhance heat transfer for this configuration. Simulations employing effective thermal conductivities and homogenized (nongeometrically accurate) meshes in the fuel regions predict cask thermal capacities that are 3 to 8% lower than the geometrically accurate CFD simulations. Basket surface temperatures calculated in this work will be used as boundary conditions in future benchmark experiments.