In this project, Large Eddy Simulation (LES) and Direct Numerical Simulations (DNS), where minimal and no turbulence modeling is employed, respectively, will be performed with Nek5000 & NeRS to investigate local flow and heat transfer behavior and provide a benchmark for lower fidelity models as well.
The Materials Management and Minimization (M3) Reactor Conversion Program of the National Nuclear Security Administration (NNSA) is supporting the conversion of the research reactor from Highly Enriched Uranium (HEU, 235U / U ≥ wt. 20%) fuel to Low Enriched Uranium (LEU, 235U / U < wt. 20% ) fuel. There are three research reactors in the world actively engaged in conversion that utilize involute shaped fuel elements: the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR) located in Tennessee, U.S.A.; the Laue-Langevin Institute (ILL) High Flux Reactor (RHF) located in Grenoble, France and; the Technical University of Munich (TUM) Research Neutron Source Heinz Maier-Leibnitz (FRM II) located in Garching, Germany. These reactors share a similar configuration of coolant channel, which is of extremely thin thickness and involute shape.
Better understanding of flow behavior and heat transfer mechanisms such as coolant mixing in the corner of the coolant channels is of great interest and importance for the design of LEU fuel elements since this is where minimum safety margins occur. It is also of fundamental interest due to the presence of turbulence driven secondary flows that impact the rates of transfer of heat and momentum.
Nek5000 is a Gordon Bell and R&D 100 prize-winning code with high accuracy and demonstrated scaling to millions of processors. NekRS is a new version of Nek5000 that is targeting extreme-scale computers, including multicore and many-core platforms and graphics processing units (GPU). The two codes are developed as part of the High-Order Methods for HighPerformance Multi-physics Simulations project supported by the DOE Applied Math Research base program as well as a collaboration with Nuclear Energy Advanced Modeling and Simulation (NEAS) program. Both codes include advanced algorithms, scalable iterative solvers and high-order discretization that enable scientists to efficiently simulate turbulence on the world’s leadership-class supercomputers. These capabilities will reduce the time it takes to validate and certify new reactor designs, enabling an efficient conversion process. The performance of the codes have been extensively tested and demonstrated in previous ALCC projects.