Validation of computational fluid dynamics bypass flow predictions with the Idaho National Laboratory matched index of refraction flow facility

Core bypass flow in a high temperature gas-cooled reactor (HTGR) is a key phenomena to consider in the design and licensing of these systems. Coolant gas can flow through gaps between structural graphite blocks, bypassing the heated core region. This can lead to increased fuel temperatures in the core and increased coolant temperatures at the core outlet, which can both lead to system damage if they are not accounted for. Multiple simulation studies have analyzed core bypass flow in HTGRs. These studies, however, have been limited by a lack of validation with bypass flow experiments. This work aims to begin to fill the validation gap for bypass flow predictions using the Idaho National Laboratory Matched Index of Refraction facility. This facility represents a unit-cell of a prismatic HTGR core. It includes nine coolant channels, one vertical gap, and one horizontal gap with nominal gap widths of 6.05 and 2.02 mm, respectively. Three flow rates are presented in the laminar, transitional, and turbulent regimes. Computational Fluid Dynamics simulations are performed with large eddy simulation, k−ϵ Reynolds-averaged Navier–Stokes, and k−ω Reynolds-averaged Navier–Stokes. Measurements of bypass flow, velocities, and pressure drops are compared between the simulations and the experiment. Overall, good agreement with the experimental data is achieved.