Argonne-led team models fluid dynamics of entire SMR core

June 9, 2021, 7:00AMNuclear News
This image shows the individual pins in a full-core nuclear reactor simulation. (Image: ANL)

Coolant flow around the fuel pins in a light water reactor core plays a critical role in determining the reactor’s performance. For yet-to-be-built small modular reactors, a thorough understanding of coolant flow will be key to successfully designing, building, and licensing first-of-a-kind reactors.

Scientists at Argonne National Laboratory have collaborated to develop a new computer model that allows for the visualization of complex flow structure interactions in a full pressurized water SMR core at unprecedented resolution and have published the first full-core pin resolved computational fluid dynamics simulation. The milestone in the modeling project known as ExaSMR was published on April 5 in the journal Nuclear Engineering and Design and was described by ANL in a June 7 press release.

Reshaping opportunities: Limitations in raw computing power have constrained past models to specific regions of a reactor core. Large-scale, high-resolution models can yield better information about the behavior of these reactors in the high-pressure, high-temperature, and radioactive environments of the core, and better information could drive down costs to deployment.

“As we advance toward exascale computing, we will see more opportunities to reveal large-scale dynamics of these complex structures in regimes that were previously inaccessible, giving us real information that can reshape how we approach the challenges in reactor designs,” said Argonne nuclear engineer Jun Fang, an author of the study, which was published by ExaSMR teams at Argonne and Pennsylvania State University.

The team’s computations were carried out on supercomputers at the Argonne Leadership Computing Facility, the Oak Ridge Leadership Computing Facility, and Argonne’s Laboratory Computing Resource Center.

What is ExaSMR? The ultimate objective of the ExaSMR project, being conducted under the DOE’s Exascale Computing Project, is to carry out full-core multi-physics simulations on upcoming cutting-edge exascale supercomputers, such as Aurora, which is scheduled to arrive at Argonne in 2022.

ExaSMR is expected to enable high-confidence prediction of reactor conditions, including low-power conditions at startup. Exascale software known as ENRICO will link computational fluid dynamics and Monte Carlo neutron transport modules through a common interface.

Local geometry: One key aspect of SMR fuel assembly modeling is the impact of spacer grids, which create turbulent flow in PWRs, enhancing the removal of heat from the fuel.

Instead of creating a computational grid to model all the local geometric details of the spacer grid, the researchers developed a mathematical reduced-order methodology to mimic the overall impact of these structures on the coolant flow without sacrificing accuracy, according to Argonne. The method allows the researchers to scale up the simulations to an entire SMR core.

“The mechanisms by which the coolant mixes throughout the core remain regular and relatively consistent, said Argonne principal nuclear engineer Dillon Shaver. “This enables us to leverage high-fidelity simulations of the turbulent flows in a section of the core to enhance the accuracy of our core-wide computational approach.”

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