US-based advanced nuclear fuel developer Lightbridge has successfully removed its first irradiated fuel samples from the world’s largest and most powerful nuclear test reactor.

The irradiated samples were successfully extracted after being tested inside Idaho National Laboratory’s (INL) Advanced Test Reactor (ATR) on May 6, 2026. The ATR is a unique pressurized water test reactor that runs at low pressure (about 360 psi) and temperature (around 180 degrees Fahrenheit).

Its core is surrounded with a beryllium reflector that concentrates neutrons on the fuels and materials it is testing. According to Lightbridge, the samples will cool for several months before scientists begin post-irradiation examination later this year.

The results are set to provide key data supporting the development and licensing of Lightbridge’s nuclear fuel. “The data already developed at the Advanced Test Reactor is a meaningful validation of the innovation and engineering behind Lightbridge Fuel,” Seth Grae, Lightbridge president and CEO, said.

First fuel removal

The samples were irradiated using the Fission Accelerated Steady-state Testing (FAST) method. Developed at INL, FAST is an advanced technique that relies on highly enriched uranium to achieve high burnup conditions significantly faster than conventional testing methods.

Once the cooling is done, the research team will evaluate how the fuel materials behaved under prolonged irradiation. The information will help validate computer models used to predict fuel performance. It will also support regulatory licensing for commercial deployment.

According to INL, a total of 24 members of Lightbridge’s fuel engineering team and senior management were at the site as the fuel samples were removed from the reactor. The testing program is designed to confirm the safety, performance, and economic advantages of Lightbridge Fuel, compared to conventional nuclear fuel used in commercial reactors.

“The data to be collected during the planned post-irradiation examination are expected to support our ongoing fuel performance modeling activities and regulatory licensing efforts for commercial deployment of Lightbridge Fuel,” Grae continued.

Testing continues

The ATR is regarded as the world’s most powerful test reactor. It serves as one of the US’ most important nuclear research facilities. It is also developed to produce intense neutron radiation for testing reactor fuels and materials under controlled conditions.

“The data being generated from this campaign with Lightbridge contributes to the broader scientific understanding of advanced nuclear fuel performance under irradiation,” John Wagner, INL laboratory director, said.

Lightbridge Fuel is a proprietary metallic fuel tech being developed for existing light-water reactors and pressurized heavy-water reactors. The company believes that it could improve reactor safety, increase operating efficiency, and strengthen proliferation resistance compared with conventional fuel.

The company is also adapting the technology for future small modular reactors (SMRs). Many governments and energy companies view SMRs as an important source of carbon-free electricity.

Wagner highlighted the project’s importance. “Public-private partnerships of this kind are central to INL’s mission of accelerating the development of new nuclear technologies, and we look forward to continuing this work with the Lightbridge team through post-irradiation examination and the additional testing campaigns ahead,” he concluded in a press release.

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