No surface roughness is applied. All external walls are adiabatic except as noted in the sensitivity studies. The surface facing the reader in Figure 4 is a symmetry plane. Internal vertical walls are positioned within the fuel and rack region to separate zones of different fuel ages and to align the flow vertically. These internal walls use a no-shear boundary condition since all flow resistance within the racks and fuel is accounted for by the porous model.
Air exits the model at the opposite end of the building.
The working fluid is air modeled as an ideal gas. The temperature-dependent thermal properties are given in Table 2. This assumption is valid as long as the temperatures do not go significantly above the values in the table. CFD modeling of the details of every bundle in a fuel pool is impractical because of memory and processor limitations. To simplify the model, a homogenous nonisotropic porous medium is used to represent the racks and fuel.