Researchers are modeling coolant flow and heat transfer in the thin, curved channels of research reactors—providing safer design benchmarks and helping convert reactors from highly enriched to safer low-enriched uranium fuel.
The Materials Management and Minimization (M3) Reactor Conversion Program of the National Nuclear Security Administration (NNSA) is supporting the conversion of research reactors from Highly Enriched Uranium (HEU, 235U / U ≥ wt. 20%) fuel to Low-Enriched Uranium (LEU, 235U / U < wt. 20% ) fuel. The reactors that utilize involute-shaped fuel plates 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 in these coolant channels is of great interest and importance for the design of LEU fuel elements.
Reynolds-averaged Navier–Stokes (RANS) approaches have exposed both the practicability and the limitations on the prediction of the turbulent flows. Discrepancy are found between RANS simulations with different turbulence models, flow conditions and codes. Due to the lack of relevant experimental data, it is difficult to provide best practice guidelines (BPGs) for minimizing turbulence modeling uncertainties. By performing high fidelity simulations (LES & DNS), the behavior of turbulent flows can be investigated with fewer modeling assumptions, potentially providing more reliable benchmarks for engineering predictions and more accurate thermal hydraulic safety analyses. Moreover, the database generated from the high-fidelity simulations can be used to select or refine the coefficients used in the system codes. LES database enrichment is essential for understanding the fundamental mechanisms of the flow and heat transfer behavior in involute-shaped plate research reactors under various conditions.
The simulations in this project will be performed with both Nek5000(CPU) and NekRS(GPU). Both codes have won an R&D 100 Award. These codes are developed as part of the High-Order Methods for High- Performance 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 (NEAMS) program. This project can expand the application of Nek5000 and NekRS to Research Reactor Conversion Program and attract more attention from either industry partner or university to NEAMS code as a surrogate for expensive commercial code or separate engineering applications where experimental data is limited.