ExaSMR simulation toolkit advances nuclear reactor design

Alternate options to carbon-producing vitality sources have gotten ever extra crucial as local weather change reveals its results on the Earth and in our day by day lives. Though fossil fuels nonetheless generate a lot of the electrical energy in the US, utilities are more and more including renewable sources similar to wind and photo voltaic to their vitality portfolios.

In 2021, 20% of the nation’s electrical energy got here from renewables vs. 61% from fossil fuels. However by 2050, each are projected to produce 44% as renewables proceed to surge and fossil fuels decline.

The place does that go away old style nuclear vitality?

For the previous 20 years, fission reactors have produced an almost unchanging portion of the nation’s electrical energy: round 20%. However that proportion may begin rising quickly as new design approaches and reactor applied sciences promise to remodel the nuclear energy trade.

The arrival of small modular reactors (SMRs) and superior reactor ideas (ARCs) indicators a brand new era of fission energy. In contrast to most industrial nuclear reactors at this time, SMRs are considerably smaller and use standardized designs, thereby decreasing building prices and manufacturing time. In the meantime, ARCs discover new applied sciences to supply fission energy extra effectively and safely. Each efforts use pc simulations to foretell the viability of proposed designs and to enhance them. However operating such fluid dynamics and neutron transport fashions could be computationally demanding and costly, thus limiting their use by trade.

Exascale SMR (ExaSMR), which is a high-performance computing (HPC) software program undertaking supported by the U.S. Division of Vitality’s (DOE’s) Exascale Computing Challenge (ECP), goals to make large-scale nuclear reactor simulations simpler to entry, cheaper to run, and extra correct than the present state-of-the-art.

“By precisely predicting the nuclear reactor gas cycle, ExaSMR reduces the variety of bodily experiments that reactor designers would carry out to justify the gas use. Largely, that is what simulation is shopping for firms: a predictive functionality that tells you the way sure options will carry out so that you simply need not bodily assemble or carry out as many experiments, that are enormously costly,” mentioned Steven Hamilton, ExaSMR undertaking chief and R&D scientist within the HPC Strategies for Nuclear Functions Group at DOE’s Oak Ridge Nationwide Laboratory (ORNL).

The ExaSMR undertaking is working to offer the nuclear trade’s engineers with the highest-resolution simulations of reactor methods thus far and in flip assist advance the way forward for fission energy.

Coupling physics codes right into a extra highly effective entire

Nuclear reactors generate electrical energy by splitting uranium nuclei to launch vitality in gas rods. Water is heated by this vitality launch and turns into scorching sufficient to show into steam that spins electricity-producing generators. ExaSMR integrates probably the most dependable pc codes accessible for modeling the completely different physics of this operation, thereby making a toolkit that may predict a reactor design’s whole fission course of. This toolkit contains Shift and OpenMC for neutron particle transport and reactor depletion and NekRS for thermal fluid dynamics.

Though most of those codes are already nicely established in science and trade, the ExaSMR crew has given them a whole HPC makeover. For the previous 6 years, researchers from ORNL, Argonne Nationwide Laboratory (Argonne), the Massachusetts Institute of Expertise, and Pennsylvania State College (Penn State) have been optimizing the codes for the brand new era of GPU-accelerated, exascale-class supercomputers, similar to ORNL’s Frontier and Argonne’s upcoming Aurora.

OpenMC’s growth has been led by Paul Romano, and important GPU-optimization work for Aurora has been carried out by John Tramm; Romano and Tramm are computational scientists at Argonne. Shift was initially authored by Thomas Evans, group chief for ORNL’s HPC Strategies for Nuclear Functions Group, and is now optimized for Frontier.

Each codes use Monte Carlo strategies—computational methods that use massive numbers of random samples to calculate the possible outcomes of fashions—to simulate how neutrons that transfer by means of the nuclear reactor work together with isotopes, similar to uranium, and trigger the fission occasions that create warmth within the reactor’s gas rods. The 2 codes additionally mannequin how these isotopes evolve over time, which predicts the reactor’s life span.

NekRS—a computational fluid dynamics solver developed by Elia Merzari, affiliate professor of nuclear engineering at Penn State—primarily describes how the water will transfer and behave when heated by the reactor’s gas cylinders. The ExaSMR crew’s ENRICO (Exascale Nuclear Reactor Investigative Code), additionally developed by Romano, permits OpenMC and NekRS to work together.

“What we’re doing in ExaSMR is a coupled physics simulation between the neutron transport and the fluid dynamics—you may have these two physics codes which might be speaking forwards and backwards to one another,” Hamilton mentioned. “The neutron transport is telling you the place the warmth is generated. That warmth turns into a supply time period for the fluid dynamics calculation. The fluid dynamics tells you what temperature is ensuing from that warmth supply. After which you’ll be able to alter the parameters within the simulation till each the neutron transport and the fluid dynamics are in settlement.”

ExaSMR’s means to precisely mannequin in excessive decision the entire reactor course of—thus predicting how a lot warmth the reactor’s fission occasions will produce, the power of the reactor to switch that warmth to energy turbines, and the life expectancy of the complete system—gives engineers with key insights to make sure the security and effectivity of their reactor designs.

Planning forward to keep away from obstacles

When the ECP and the ExaSMR undertaking began in 2016 to organize software program apps and instruments for exascale methods, these supercomputers did not exist but—not even on paper. The crew was challenged with figuring out tips on how to greatest optimize codes for methods that had been years away from being finalized.

“At first of the undertaking, we did not even know precisely what the architectures of the exascale machines would seem like,” Hamilton mentioned. “It was positively a problem to design our codes whereas wanting forward with confidence that we’d be capable to run successfully on the upcoming methods.”

The crew confronted not solely the duty of coupling these separate codes for his or her new use-case state of affairs of large-scale, high-fidelity reactor simulations but in addition the problem of adapting them to new computing architectures with but unknown processors. This uncertainty meant pushing the bounds of compilers and software program packages by testing use circumstances that had been far past what the software program had been examined for on the time—and it started an ongoing means of fixed communication.

“It required us to work together and iterate with the {hardware} distributors and the businesses that produce the software program to make it possible for their merchandise can deal with our use circumstances. Now we have researchers who’ve been in nearly day by day contact with people who find themselves writing compilers for the machines and making an attempt to determine points and implement options which might be wanted to compile and run our codes,” Hamilton mentioned.

Success eventually

The crew’s interplay with distributors and builders paid off with substantial enhancements within the strategies and algorithms utilized by the codes, yielding massive good points in efficiency. With its preliminary runs on Frontier, ExaSMR blew previous the crew’s speedup targets for its codes.

Shift carried out SMR simulations on as much as 8,192 nodes of Frontier and concerned simulating over 250 billion neutron histories per iteration. The efficiency achieved in these simulations is greater than 100× that of the baseline simulations carried out on the Titan supercomputer (i.e., the US’s strongest supercomputer in 2016) and greater than double the efficiency enchancment objective of fifty× from Titan to Frontier.

NekRS carried out SMR simulations on as much as 6,400 nodes of Frontier, together with the most important reactor fluid-flow simulation carried out thus far with over 1 billion spatial parts. The height efficiency on Frontier displays a greater than 125× enchancment over corresponding baseline simulations carried out on Titan.

What’s forward for ExaSMR?

Partnering with Westinghouse, which is a producer of economic nuclear energy expertise, the ExaSMR crew utilized for a DOE Workplace of Superior Scientific Computing Analysis Management Computing Problem grant. Westinghouse desires to judge the impression of utilizing higher-enrichment gas than what’s presently used of their reactors. Working ExaSMR on Frontier will enable them to carry out high-fidelity simulations to foretell how several types of fuels would carry out if utilized in a presently working reactor.

Likewise, Hamilton desires to use ExaSMR to present ARC applied sciences being explored within the energy trade, similar to these being developed as a part of the DOE Workplace of Nuclear Vitality’s Superior Reactor Demonstration Program. This system works with industrial firms to assist pace up the demonstration of superior reactors by offering preliminary funding. Two such reactors are slated for near-term deployment by 2027: X-energy’s Xe-100 pebble-bed reactor and TerraPower’s Natrium sodium-cooled quick reactor. 5 extra designs from Kairos, Westinghouse, BWX Applied sciences, Holtec Worldwide, and Southern Firm are ramping up for longer-term deployment.

Hamilton foresees ExaSMR changing into an indispensable instrument for firms which might be getting into a brand new period of nuclear energy.

“Numerous firms are exploring several types of reactor designs at this time, and the high-performance, high-fidelity simulations that we’re creating have a whole lot of interesting options for designers,” Hamilton mentioned. “It is unlikely, within the close to future, that we’ll have sufficient confidence in simulations that they’d totally exchange experiments, but when we are able to scale back the variety of experiments which might be carried out, then there could be enormous monetary good points for these firms.”