Features of coolant movement at the boundary of jacketless fuel assemblies with fuel rods of various diameters

The paper presents the results of experimental studies investigating the peculiarities of coolant movement at the border and in the bordering fuel rods of jacketless fuel assemblies with various fuel rod diameters and type of spacing grids (honeycomb or plate). The study focuses at the effect of the grid type and spacing of fuel rods in neighboring fuel assemblies on the hydrodynamics and mass transfer in the coolant flow. A series of experiments was performed using the created scale model of the boundary area between jacketless fuel assemblies with fuel rods of various diameters. The studies were carried out using the pneumometric method for measuring the static and dynamic flow characteristics, as well as thermocouple measurements.