Heat Emission and Temperature Non-uniformity in Rod Bundles with Different Spacing, Cooled by Heavy Liquid-Metal Coolant

Heat emission and temperature non-uniformity along the perimeter of rods in free lattices of fuel elements with heavy liquid-metal coolant are studied. The experimental data for an assembly of smooth rods, assemblies of fuel elements with spiral ribbing, and transverse lattices are analyzed. The studies show that there is almost no temperature non-uniformity in a lattice of smooth fuel elements along its perimeter, which is in contrast to the high general azimuthal temperature non-uniformity in an assembly with spacing by spiral coils. Rib spacing resulted in significant reduction of heat emission. In an assembly with transverse spacer lattices, the heat emission increases only in the region containing the lattices; in the spaces between lattices, it is approximately equal to the heat emission in a bundle with smooth fuel elements. Inside a spacer lattice, periodic temperature non-uniformities appear along the perimeter of the fuel elements; these non-uniformities are due to the fuel elements touching the elements of the lattice. A relation is recommended for calculating heat emission (Nusselt numbers) and temperature non-uniformity along the perimeter of the fuel elements for the studied methods of spacing the fuel elements.