As the dawn of exascale computing approaches, unprecedented computing power is reshaping the ways researchers cope with challenging engineering flow problems. Large-scale massively parallel simulations have now become a vital source of knowledge to complement the experiments and provide unique opportunities to advance our understanding of turbulent flows and better inform engineering designs. Several strategically important projects have been identified and are being pursued for the upcoming exascale computing platforms.  Among these, the ExaSMR project is focused on a class of nuclear power reactors known as small modular reactors (SMRs). Conventional nuclear reactors are usually limited to locations with large populations, but SMRs are customizable and could potentially provide rural areas with an efficient and affordable source of electricity. The ExaSMR project is developing tools for coupling Monte Carlo Neutronics to a Computational Fluid Dynamics (CFD) solver. It will significantly improve the ability to accurately predict and analyze how nuclear reactors function to ensure their operation is safe, reliable and economical.

The CFD calculations in ExaSMR are carried out by a state-of-the-art flow solver, Nek5000, which is an open-source, higher-order spectral element method (SEM) code developed at Argonne National Laboratory. SEM combines the accuracy of spectral methods with the domain flexibility of the finite element method. Though Nek5000 is able to simulate flow in complex engineering domains, such as the spacer grid and mixing vanes (SGMV), the focus herein is to model the effect of SGMV on fluid flow without the need of a body-fitted mesh. This approach would significantly reduce the number of elements required for domain discretization and the per-subchannel computational cost. In doing so, one can greatly expand the simulation domain (up to a full core) and study the system responses concerning the neutronics and thermal-hydraulics. Since the Reynolds number expected in the reactor core is high, it is necessary to use a RANS approach to model turbulence as the computational expense associated with resolving the turbulent fluctuations in a high-fidelity model would be prohibitively large. A newly developed regularized k-ω RANS model is adopted in the related Nek5000 calculations. The modeling of SGMV effect is achieved by implementing a three-dimensional momentum source model (MSM) in the region supposedly occupied by the SGMV. The validity of the MSM is further assessed by comparing the corresponding results with those from LES calculations on the body-fitted mesh. The current work is part of the broader efforts to leverage the supercomputing and cutting-edge CFD techniques in addressing grand challenges in nuclear engineering.


Modeling the Effect of Spacer Grid and Mixing Vanes in Coupled Cfd Simulations of Small Modular Reactors

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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