Hydrodynamic Features of the Flow Downstream from the Mixing Spacer Grid in a Kvadrat Fuel Assembly in PWRs

Abstract

The experimental investigation of local hydrodynamic characteristics of the coolant flow downstream of a mixing spacer grid (MSG) in characteristic regions of a Kvadrat fuel assembly in PWRs was performed. The importance of this investigation is due to the fact that MSGs of interest can enhance heat-and-mass transfer. Finding the best design of the grid is required for corroboration of the thermal engineering reliability and operability of the PWR core. The paper presents a description of the test facility and a model of a fuel assembly fragment, the investigation procedure, and discussion of the results. The experiments were performed in the aerodynamic test facility on a scaled model of a fragment of a Kvadrat fuel assembly by simulating the water coolant flow using an air flow according to the hydrodynamic similarity theory. Within the scope of the investigation, the transverse velocity fields in the coolant flow were studied in the characteristic cross-sections of the fuel assembly. The transverse velocity distribution was measured with a five-channel pneumometric probe that can determine the module and direction of a flow velocity vector at an investigated point. The experimental results are presented in the form of distribution of relative transverse velocity downstream of MSG in the characteristic regions of the fuel assembly, such as standard cells, guide channel, and a gap between fuel rods. Based on the experimental data, the coolant flow features have been revealed, and the regularities in the development of transverse velocity field downstream of the mixing spacer grid under investigation have been determined. These experimental data are required for assessment of the mixing spacer grid effectiveness, verification of 3D CFD-programs, and applicable cell-by-cell codes for calculation of a PWR core with a Kvadrat fuel assembly.