IDAHO FALLS, Idaho — A nearly two-year nuclear fuel testing campaign at Idaho National Laboratory has concluded with results that surpassed original performance targets, marking a significant step forward for thorium-based reactor fuel technology. Clean Core Thorium Energy completed irradiation testing of its ANEEL fuel at INL’s Advanced Test Reactor, with final results exceeding the program’s 60 gigawatt-days per metric ton of uranium burnup goal.
What Was Tested and How It Performed
ANEEL fuel is a blend of thorium and high-assay low-enriched uranium, known as HALEU, and is engineered to work in pressurized heavy water reactors without requiring any modifications to the reactor itself. The testing program, which got underway in 2024, evaluated 216 individual fuel pellets across three sequential extraction batches.
The first batch was pulled at a burnup level of 20 GWd/MTU, followed by a second extraction at more than 45 GWd/MTU. The third and final batch exceeded the 60 GWd/MTU threshold that had been set as the campaign’s primary target. That final batch is still undergoing analysis.
Post-irradiation examination results confirmed the fuel performed well under testing conditions. Notably, some of the test rodlets demonstrated superior fission gas retention compared to conventional uranium dioxide fuel — a meaningful performance indicator in nuclear fuel evaluation. The burnup level achieved is more than eight times the typical discharge burnup seen in standard pressurized heavy water reactor and CANDU reactor operations, representing a substantial potential improvement in fuel efficiency.
Kelley Walker, the principal investigator on the project, said the milestone reflected years of preparation. “This final portion of the irradiation experiment has been several years in the making, and I congratulate Clean Core on their major accomplishment,” Walker said.
Why This Matters for Nuclear Energy Development
Clean Core CEO Mehul Shah described clearing the 60 GWd/MTU threshold as a critical marker for the overall fuel program. “Surpassing 60 GWd/MTU of burnup in the Advanced Test Reactor marks an important milestone for the ANEEL fuel program,” Shah said.
The significance of testing at INL’s Advanced Test Reactor cannot be understated in the context of the broader nuclear energy landscape. The ATR, one of the most capable research reactors in the world, has long served as a proving ground for fuel concepts aimed at improving the performance and economics of nuclear power generation. INL, located in eastern Idaho, is a central hub for the nation’s nuclear research and development infrastructure.
ANEEL fuel’s compatibility with existing pressurized heavy water reactors — including CANDU-type reactors deployed globally — without requiring hardware changes could significantly lower the barriers to adoption. Utilities operating those reactor designs would not face the cost and complexity of physical modifications to use the new fuel type, which backers argue makes the technology commercially viable at a faster timeline than alternatives that require purpose-built reactors.
Thorium-based fuels have attracted renewed interest from both government and private sector researchers in recent years as part of broader efforts to diversify nuclear fuel cycles, reduce dependence on conventional uranium supply chains, and improve overall reactor performance metrics.
What Comes Next
With laboratory-scale irradiation testing now complete, Clean Core’s next step is a demonstration irradiation conducted inside an operating commercial power reactor. That phase would move the fuel from research validation toward real-world deployment readiness. Analysis of the final fuel batch from the ATR campaign remains ongoing, and those results are expected to further inform the path to commercialization.
For INL and Idaho’s role in the national nuclear energy conversation, the completed campaign adds to a growing portfolio of advanced fuel and reactor research being conducted at the eastern Idaho facility. The lab continues to serve as a centerpiece of domestic nuclear innovation as the country weighs energy independence and next-generation power generation. For additional coverage of Idaho energy developments, visit Idaho News.