Scientists at two U.S. national laboratories have built a new software tool called Griffin that can simulate nuclear reactors in a computer. The tool helps engineers test reactor safety and performance without building expensive physical prototypes. It recently won a 2025 R&D 100 Award.
Researchers at Idaho National Laboratory and Argonne National Laboratory jointly developed Griffin. The software is part of a bigger effort by the U.S. Department of Energy to support next-generation nuclear reactor designs.
Building a physical nuclear reactor is costly and takes years. Developers need a safe way to test whether their designs will work before spending millions on construction. Griffin solves this by running detailed computer simulations.
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The software models what happens inside a working reactor. It tracks neutrons, heat, fuel changes, and how materials behave under extreme conditions. Argonne principal nuclear engineer Changho Lee said Griffin simulates real-life scenarios where high temperatures and pressure change fuels and materials over time.
Griffin works for many types of reactors. These include pebble bed reactors, molten-salt reactors, fast reactors cooled by sodium or lead, and small microreactors. Engineers can also use it to study how the entire cooling system behaves outside the reactor core.
The tool has limits. It is a simulation, so its predictions must be checked against real-world experiments. Researchers continue to compare Griffin’s results with physical measurements to improve its accuracy.
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Griffin matters because it helps researchers, companies, and regulators test new reactor designs faster and cheaper. The 2025 R&D 100 Award winning software also supports NASA projects for space exploration, including nuclear rockets for missions to the moon and Mars.
