Exascale Simulations of Fusion and Fission Systems

TL;DR

This paper presents exascale heat and fluid flow simulations of fusion and fission systems using NekRS, demonstrating unprecedented scale and new high-order overset grid techniques on top-tier supercomputers.

Contribution

It introduces scalable exascale simulations of fusion and fission systems with NekRS, including the first use of high-order overset grids at such scale.

Findings

Achieved over 1 trillion degrees of freedom in simulations.

Demonstrated scalability of NekRS on Frontier and Aurora.

First application of high-order overset grids at exascale.

Abstract

We discuss pioneering heat and fluid flow simulations of fusion and fission energy systems with NekRS on exascale computing facilities, including Frontier and Aurora. The Argonne-based code, NekRS, is a highly-performant open-source code for the simulation of incompressible and low-Mach fluid flow, heat transfer, and combustion with a particular focus on turbulent flows in complex domains. It is based on rapidly convergent high-order spectral element discretizations that feature minimal numerical dissipation and dispersion. State-of-the-art multilevel preconditioners, efficient high-order time-splitting methods, and runtime-adaptive communication strategies are built on a fast OCCA-based kernel library, libParanumal, to provide scalability and portability across the spectrum of current and future high-performance computing platforms. On Frontier, Nek5000/RS has achieved an unprecedented milestone in breaching over 1 trillion degrees of freedom with the spectral element methods for the simulation of the CHIMERA fusion technology testing platform. We also demonstrate for the first time the use of high-order overset grids at scale.