Temperature distributions in an idealized nuclear fuel assembly were computed and studied parametrically. The assembly, which consists of a square array of spacer-free fuel elements, is bounded by an assembly wall and is cooled by longitudinal liquid metal flow. A single-region multicell analysis is used to predict the influence of the fuel assembly wall on the temperature distributions and Nusselt numbers in the idealized assembly. An analytical series solution method couples adjacent cellular temperature-field solutions, and boundary conditions on these and other irregular boundaries are satisfied using a least-squares matching technique. Two slug flow coolant models are considered in the analysis. A global slug flow model assumes a uniform coolant velocity. A cellular slug flow model assigns to each cell a velocity based on its hydraulic diameter. Results of this analysis show that the temperature distributions across the fuel assembly and around each individual fuel element are most strongly influenced by the cellular mass flow rate distribution, which is characterized by a single parameter—the cellular mass flow rate ratio. Fuel assembly temperature gradients are minimized if this ratio is chosen equal to unity. Computations of cellular Nusselt numbers indicate that while steep thermal gradients may exist across the fuel assembly, the Nusselt numbers of all but the cell closest to the wall are unaffected by the presence of the wall. Cellular Nusselt numbers, cellular coolant bulk temperatures, and fuel-element wall temperatures are presented for a range of pitch-to-diameter and cellular mass flow rate ratios.