In this work, a 3D, one-eighth homogenous fuel CFD model of the TN-32 UNF cask is constructed, and simulations are performed as part of the Extended Storage Collaboration Program (ESCP). The simulations are carried out using ANSYS/FLUENT1 package with geometry and boundary conditions recommended by ESCP. Simulation results, including external and internal cask temperatures, are compared with experimental data from the High-Burnup (HBU) project. A preliminary sensitivity analysis is conducted to determine the effect the different assumptions/simplification proposed by ESCP on the cask temperatures. This sensitivity analysis indicates that the cask internal natural convection has a significant effect on the prediction of internal temperatures when the drain holes at the base of the basket are modeled. Additionally, the results indicate that a small variation in the thickness of the peripheral basket-rail gap has a significant effect on the internal temperatures. The best simulation model is shown to include modeling of the drain holes, natural convection, a peripheral basket-rail gap of 4.78 mm (0.188 inch), and omission of the base inner liner-gamma shield gap.