Validation of NEK5000 for 37- And 61-pin wire-wrap geometries with conjugate heat transfer

The turbulent mixing modeling for unsteady heat transfer problems in thermal-hydraulics has long been a focus in nuclear engineering community. One of the promising approaches that takes a full advantage of recent advances in HPC is the use of hierarchy of fidelity simulations that are cross-verified and validated in the regimes of interest. In particular, it is beneficial to have a higher fidelity reference simulation that could be used for benchmarking of the faster-turn-around lower-fidelity tools. Another good use of (validated) high-fidelity models that are less dependent on parameter and geometry perturbations than their lower-fidelity counterparts is to provide closure relations for reduced-order and -fidelity approaches where experiment data is either incomplete or not yet available. Here we report Nek5000 LES validation simulations for 37-pin and 61-pin wire-wrap conjugate heat transfer geometries. As a part NEAMS TH component of the SHARP multi-physics toolkit V&V-driven development, we have conducted a series of isothermal single wire-wrap pitch and multi pitch conjugate heat transfer calculations scaled up to 1 million MPI ranks with Reynolds number up to 120,000. The 37-pin 4-wire-wrap PLANDTL sodium experiment LES campaign was conducted as a part of the advanced M&S activity of CNWG under the U.S.-Japan Bilateral Commission Civil Nuclear Cooperation on advanced reactor R&D between DOE and JAEA. Originally funded by Nuclear Infrastructure Council (NIC) Cost-Share Award, the 61-pin FOA project was a joint venture with TerraPower, Texas A&M University, AREVA, and Argonne National Laboratory, a well-defined first-of-a-kind validation campaign for the CFD TH modeling of hexagonal packed fuel assemblies with helically wire-wrapped pin SFR geometries for both conjugate heat transfer and high-resolution isothermal validation.