Water velocity determination in the gaps of irt-3M, -4M fuel assemblies

Experiments on measuring the water velocity in the gaps between the fuel elements of an IRT-3M eight-tube fuel assembly with 90% fuel enrichment, used in pool and tank research reactors, are described. The experiments were performed on a hydraulic facility at the National Research Center Kurchatov Institute. The velocity was determined from the dynamic head in the gaps of a model fuel assembly. These velocities were used as a basis for determining the water flow rate in each gap and the total flow rate through a fuel assembly. Comparative hydraulic calculations of IRT-3M fuel assemblies with 90% fuel enrichment and IRT-4M fuel assemblies with 19.7% enrichment, developed as a replacement for IRT-3M, are described. It is shown that if the IRT-4M gaps decrease to 1.85 mm, then the water velocity in them will decrease by only 5% as compared with IRT-3M.