Understanding the physical behavior in a running nuclear reactor can be improved through simulations on a supercomputer, says Jared Sagoff
Scientists who want to build new generations of small modular reactors (SMRs) must be able to design and understand how these reactors will behave in simulated environments before they can be built. Large-scale, high-resolution models provide information that can reduce the cost of building a new, intrinsically safe nuclear reactor.
Scientists at the Argonne National Laboratory (ANL) of the US Department of Energy (DOE) have jointly developed a new computer model that enables the visualization of a complete reactor core with unprecedented resolution. The goal of the project, which is being carried out under the auspices of the DOE’s Exascale Computing Project (ExaSMR), is to run full-core multi-physics simulations on upcoming state-of-the-art exascale supercomputers. This includes Aurora, which is in Argonne. should arrive
in 2022.
An update on the progress made was published in the journal Nuclear Engineering and Design in April, which will hopefully inspire researchers to further integrate high-fidelity numerical simulations into actual engineering designs.
Modeling in detail
In a nuclear reactor, the eddies and eddies of coolant that circulate around the fuel rods play a critical role in determining the thermal and hydraulic performance of the reactor. They also provide nuclear engineers with much-needed information on how best future nuclear reactor systems can be designed for both normal operation and stress tolerance.
A typical light water reactor core consists of nuclear fuel elements, each containing several hundred individual fuel rods, which in turn consist of fuel pellets. Previously, the limitations of raw computing power limited the models so that they could only address certain regions of the core. But now an image can model all the individual pins in one of the first full-core reactor simulations.
“As we advance toward exascale computing, we will see more opportunities to uncover the dynamics of these complex structures on a large scale in previously inaccessible regimes, which will give us real information that can reshape our approach to the challenges of reactor design,” said Argonne Nuclear engineer Jun Fang, an author of the study published by ExaSMR teams in Argonne and Professor Elia Merzari’s group at Pennsylvania State University.
A key aspect of SMR fuel bundle modeling is the presence of spacer grids. These grids play an important role in pressurized water reactors such as the SMR under consideration, as they create structures of turbulence and improve the ability of the flow to remove heat from the fuel rods.
Rather than creating a computational grid that resolves all local geometric details, the researchers developed a mathematical mechanism to reproduce the overall impact these structures have on coolant flow without sacrificing accuracy. The researchers were able to successfully scale the associated CFD simulations of numerical fluid mechanics to a complete SMR core for the first time.
“The mechanisms by which the coolant mixes through the core remain regular and relatively constant. This allows us to use high fidelity simulations of the turbulent flows in a section of the core to improve the accuracy of our core-wide computational approach, ”said Dillon Shaver, Argonne’s chief nuclear engineer.
The ExaSMR teams’ technical expertise builds on Argonne’s history of breakthroughs in related research areas such as nuclear engineering and computer science.
A few decades ago, a group of Argonne scientists led by Paul Fischer pioneered a CFD flow solver software package called Nek5000, which was transformative in allowing users to simulate engineering fluid problems with up to a million parallel threads . Recently, the Nek5000 was redesigned to a new solver called NekRS, which uses the power of graphics processing units (GPUs) to increase the computing speed of the model. “With codes developed for this specific purpose, we can take full advantage of the raw computing power that the supercomputer offers us,” said Fang.
The team’s calculations were performed on supercomputers at the Argonne Leadership Computing Facility (ALCF), Oak Ridge Leadership Computing Facility (OLCF), and Argonne Laboratory Computing Resource Center (LCRC). The ALCF and OLCF are DOE Office of Science User Facilities. The research is supported by the Exascale Computing Project, a cooperation between the Office of Science of the DOE and the National Nuclear Security Administration.
Jared Sagoff is the coordinating writer / editor at Argonne National Laboratory
Supercomputers at the ALCF Copyright: Argonne National Laboratory
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