Nek5000 Large-Eddy Simulations for Thermal-Hydraulics of Deformed Wire-Wrap Fuel Assemblies

A well-characterized validation program has been defined for the thermal-hydraulic CFD modeling of 61-pin hexagonal packed fuel assemblies with helically wire-wrapped pins for both non-deformed beginning-of-life geometries and deformed later-in-life geometries typical of sodium-cooled fast reactors. The motivation for this work is the need to validate CFD codes to accurately model the flow and thermal performance of wire-wrapped fuel assemblies, particularly the deformed later-in-life bundles. The effect of pin and duct deformation is increasingly important as reactor designs look toward longer assembly lifetimes. As a part of a larger collaborative project with TerraPower, Texas A and M University (TAMU), and AREVA, this validation work consists of CFD simulations of four con-current experiments. Pre-test numerical simulations corresponding to each of the experiments has been conducted and are planned to be followed by post-test simulations that will incorporate test information as it becomes available to account for any as-built differences in geometry of test section and its specifications including the differences in boundary conditions of the actual tests. This paper focuses on Nek5000 LES results for the isothermal/TAMU undeformed configuration as a first step toward and initial conditions for the deformed isothermal/TAMU and/or conjugate heat transfer/AREVA cases. (authors)