Experiments performed by others measured the temperature of an 8×8 array of horizontal heated rods in air within a constant temperature enclosure. That apparatus was a scaled-down model of a spent boiling water reactor fuel assembly in a transport package. In the current work, three-dimensional computational fluid dynamics simulations of natural convection and radiation heat transfer within this domain were conducted to determine appropriate boundary conditions and benchmark the results. Initial simulations employed nearly equal specified temperatures on the walls and endplates, and insulated rod ends. They accurately reproduced the shapes of the temperature profiles in the midplane between the rod ends, but over-predicted the temperature level at the highest heat load. Simulations that included conduction within the endplates and convection from their outside surfaces more accurately modeled heat losses. They brought the midplane temperatures at the highest heat load to the measured data once an appropriate convection coefficient was determined. The simulation technique will be used to design future experiments that model heat transfer from spent fuel assemblies to highly-non-isothermal support structures.

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