Coolant Mixing in Multirod Fuel Bundles

The report gathers together the available experimental data in the literature on mixing rates between sub-channels for axial flow in multi-rod fuel bundle assemblies both with and without mixing promoters. The data are compared to mixing rates predicted by various methods. The data for mixing around bare rods, without mixing promoters, is somewhat erratic and hard to predict within a factor of 3.

Mixing with fins or wire wraps, however, seems more systematic and easier to predict. In the range of data available, predictions seem to be as good as ± 50Jf.