Full-Core Computational Fluid Dynamics Simulations Using NekRS

With the ever-increasing availability of computing power, the size and fidelity of possible simulations in nuclear engineering has been expanding. With each increase, the complexity of phenomena that can be analyzed and better understood also grows. The field of computational fluid dynamics is no different. Simulations of full assemblies that were considered “hero-class” calculations only a few years ago, are now commonplace. It was only a matter of time until full-core-scale simulations became possible. Recent efforts driven jointly by the U.S. Department of Energy's Exascale Computing Project (ECP) and Nuclear Energy Advanced Modeling and Simulation (NEAMS) Program have enabled these simulations. In this paper, we describe the application of computational fluid dynamics to perform full-core large eddy simulations (LES) of pebble bed reactors, Reynolds-averaged Navier-Stokes simulations of a light water small modular reactor, LES of a molten salt fast reactor and LES for a liquid metal microreactor. Additionally, we describe the physical insights gained from each simulation and how the results are being used to drive the next generation of nuclear engineering simulation tools.