Particle Image Velocimetry of Fluid Flow in an 85-Pin Hexagonal Rod Bundle with Spacer Grids for a Gas-Cooled Fast Modular Reactor

Abstract

The Department of Energy Integrated Research Project (IRP) is developing a 50 MWe helium-cooled fast modular reactor (FMR), and has tasked Texas A&M University with conducting the thermal-hydraulic characterization of the baseline core configuration of the FMR. The experimental thermal-hydraulic investigation consisted of the axial and radial flow field characteristics in the hexagonal fuel rod bundle composed of 84 fuel rods, a central control rod, and spacer grids at a Reynolds number of 12,000. The experimental facility resembles one unit of the total fuel assembly and was constructed to be fully transparent to perform optical measurements. Time-Resolved Particle Image Velocimetry (TR-PIV) measurements were used to characterize hydraulic behavior downstream the spacer grid. In each orientation, using the PIV velocity vector fields, the full-field flow statistics were computed for the mean velocity, vorticity, and Reynolds stresses. An analysis of the energy decay downstream of the spacer grid was conducted with calculations of secondary-flow intensities, turbulent kinetic energy, power spectrum density, and spatial-temporal velocity cross correlations. Analysis in the two dimensional axial and radial flow statistics allowed for three dimensional conclusions and is shown in a 3D vorticity model. The data from this experimental campaign will be used to to validate numerical models based on Computational Fluid Dynamics (CFD) and other codes.