Accelerating Design for Small Modular Reactors and Advanced Reactor Concepts

PI: Steven Hamilton,
Oak Ridge National Laboratory

In 2016, the US Department of Energy’s (DOE’s) Exascale Computing Project (ECP) set out to develop advanced software for the arrival of exascale-class supercomputers capable of a quintillion (10¹⁸) or more calculations per second. That meant rethinking, reinventing, and optimizing dozens of scientific applications and software tools to leverage exascale’s thousand-fold increase in computing power. That time has arrived as the first DOE exascale supercomputer—the Oak Ridge Leadership Computing Facility’s (OLCF’s) Frontier—opens to users around the world. “Exascale’s New Frontier” explores the applications and software technology for driving scientific discoveries in the exascale era.

The Science Challenge

The advent of small modular reactors (SMR) and new advanced reactor concepts (ARC) signals a new generation of fission power. Unlike most commercial nuclear reactors today, SMRs are substantially smaller and use standardized designs, which reduces construction costs and time to production. ARCs explore new technologies to produce fission power more efficiently and safely. Both efforts utilize computer simulations to predict the viability of proposed designs and to improve them. But running such fluid dynamics and neutron transport models can be computationally demanding and expensive, limiting their usage by industry.

Why Exascale?

The ExaSMR toolset integrates the most accurate computer codes for modeling the different physics involved in nuclear reactors—OpenMC and Shift for neutron particle transport and reactor depletion, and NekRS for thermal fluid dynamics. The ExaSMR team has optimized these codes for exascale supercomputers, aiming to provide design engineers with the highest resolution simulations of nuclear systems to date. ExaSMR also promises much faster turnaround times and the ability to perform a larger number of simulations—and in turn advance the future of fission power much sooner.

“By accurately predicting the nuclear reactor fuel cycle, ExaSMR reduces the number of physical experiments that reactor designers would perform to justify the fuel use. In large part, that’s what simulation is buying companies: a predictive capability that tells you how certain features will perform so that you don’t need to physically construct or perform as many experiments, which are enormously expensive,” said Steven Hamilton, ExaSMR project leader and R&D scientist in the HPC Methods for Nuclear Applications Group at DOE’s Oak Ridge National Laboratory (ORNL).

Frontier Success

Over the course of the project, substantial improvements in the methods and algorithms used by the codes have led to very large gains in performance. Shift performed SMR simulations on as many as 8,192 nodes of Frontier, simulating over 250 billion neutron histories per step at that scale. The performance achieved in these simulations is more than 100× that of the baseline simulations performed on the Titan supercomputer (i.e., the US’s most powerful supercomputer in 2016) and more than double the performance improvement goal of 50× from Titan to Frontier. NekRS performed SMR simulations on up to 6,400 nodes of Frontier, including the largest reactor fluid-flow simulation performed to date with over 1 billion spatial elements and a total of 350 billion degrees of freedom. The peak performance on Frontier reflects a more than 100× improvement over corresponding baseline simulations performed on Titan.

Total neutron interaction rate throughout SMR core computed by Shift.

Fluid swirling downstream of mixing vanes computed by NekRS.


What’s Next?

Partnering with Westinghouse, a producer of commercial nuclear power technology, the ExaSMR team has applied for a DOE Office of Advanced Scientific Computing Research Leadership Computing Challenge grant. Westinghouse wants to evaluate the impact of fuel enriched to higher levels of fissile uranium-235 than that currently used in its reactors. Running ExaSMR on Frontier will allow them to perform high-fidelity simulations to predict how these different types of fuels would perform if used in a current operating reactor.

Likewise, Hamilton wants to apply ExaSMR to current ARC technologies being explored in the power industry, such as those being developed as part of the DOE Office of Nuclear Energy’s Advanced Reactor Demonstration Program. The program works with commercial companies to help speed up the demonstration of advanced reactors by providing initial funding.

Hamilton foresees ExaSMR becoming an indispensable tool for companies that are entering a new era of nuclear power.

“Various companies are exploring different types of reactor designs today, and the high-performance, high-fidelity simulations that we’re developing have a lot of appealing features for designers,” Hamilton said. “It’s unlikely, in the near future, that we’ll have enough confidence in simulations that they would fully replace experiments, but if we can reduce the number of experiments that are performed, then there can be huge gains for these companies.”

Support for this research came from the Exascale Computing Project, a collaborative effort of the DOE Office of Science and the National Nuclear Security Administration, and the DOE Office of Science’s Advanced Scientific Computing Research program. The OLCF is a DOE Office of Science user facility.

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