Spectral element applications in complex nuclear reactor geometries: Tet-to-hex meshing

•Applying tet-to-hex meshing method to SEM CFD code Nek5000 for complex nuclear-related geometries.•Boundary layers were created to obtain good near wall resolution.•Several example cases, including fuel assemblies, helical coil steam generator, random packed pebble bed, are simulated with Large Eddy Simulation, showing the capability of tet-to-hex meshing method of handling complicated geometry.•In most of the presented cases, experimental data was presented along with numerical data. In general, a good agreement was obtained, validating the accuracy of the tet-to-hex meshing method.•Compare to an ill-designed block mesh, tet-to-hex mesh is more robust and numerical efficient.