For the first time in decades, thorium-based nuclear fuel is headed for fabrication and reactor testing on U.S. soil. Clean Core Thorium Energy, a company developing thorium-uranium oxide fuel for heavy water reactors, has secured federal environmental clearance to irradiate roughly a dozen test specimens at Idaho National Laboratory. Fabrication of the fuel pellets is underway at Texas A&M University, and the rodlets are destined for accelerated burn-up trials designed to compress years of reactor service into a fraction of the time.
The milestone, confirmed by a Department of Energy categorical exclusion determination published in spring 2026, marks the furthest any thorium fuel program has advanced through the U.S. regulatory pipeline since the experimental thorium cores that ran at Shippingport and Indian Point 1 were shut down in the 1980s.
Why thorium, and why now
Thorium is roughly three to four times more abundant in the Earth’s crust than uranium. When blended with fissile uranium in a reactor, thorium-232 absorbs neutrons and converts into uranium-233, which sustains the chain reaction. Proponents argue that thorium fuel cycles can produce less long-lived radioactive waste and offer inherent proliferation resistance because the process generates uranium-232 as a byproduct, a powerful gamma emitter that makes the material difficult to handle and divert.
Despite those theoretical advantages, thorium fuel has never reached commercial scale. India has pursued thorium research for decades to leverage its vast domestic reserves, and Canada’s heavy water reactor fleet has hosted small-scale thorium experiments. But no country operates a commercial thorium-fueled power plant today. The Clean Core program is an attempt to change that by generating the hard irradiation data that regulators and utilities require before any fuel can be licensed for routine use.
Federal clearance and what it covers
The DOE determination, numbered DOE-ID-INL-20-068 R1, formally authorizes an accelerated burn-up test of Clean Core’s proprietary ANEEL-Fuel. Under the National Environmental Policy Act, a categorical exclusion means DOE reviewers concluded the test poses no significant environmental impact and does not require a full environmental impact statement. That procedural green light allows physical work to proceed without additional NEPA hurdles.
The determination specifies that approximately 12 rodlets, small sealed tubes containing pressed and sintered fuel pellets, will serve as test specimens. The fuel matrix pairs thorium oxide with uranium oxide at defined ratios and includes burnable absorber materials to help manage reactivity. Twelve rodlets is a modest batch, large enough to characterize fuel behavior across a range of conditions but well short of a commercial-scale production run.
Where the fuel is being made
Texas A&M University’s Fuel Cycle and Materials Laboratory, housed within its nuclear engineering department, is handling pellet fabrication. The lab operates gloveboxes, high-temperature sintering furnaces, and hot cells rated for actinide-bearing materials, giving it the equipment and regulatory clearances needed to press ceramic fuel pellets and load them into test-ready rodlet assemblies.
Placing an academic research lab at the center of a fuel qualification campaign is not unusual for early-stage nuclear programs. University facilities often bridge the gap between bench-scale research and the industrial fabrication lines that would be needed for full production. If the irradiation results are favorable, the data generated at Texas A&M and INL could feed directly into commercial licensing applications.
Testing infrastructure at Idaho National Laboratory
INL operates two facilities well suited to this kind of work. The Transient Reactor Test Facility, known as TREAT, was restarted in 2017 after sitting idle for more than 20 years. TREAT can subject fuel samples to rapid power excursions that mimic accident conditions, generating data on cladding failure thresholds and fission gas release under extreme transient heating. INL’s Advanced Test Reactor, meanwhile, provides steady-state irradiation slots where rodlets can accumulate burn-up over extended campaigns, simulating the gradual wear of normal reactor operation.
Recent international collaborations underscore how active this testing ecosystem has become. A joint U.S.-Japan program produced the first modern safety tests of fast-reactor fuels in two decades, demonstrating that INL’s revived infrastructure can support complex, multi-step irradiation campaigns. The ANEEL-Fuel program is positioned to draw on that same capability, though the specific sequence of tests, whether rodlets will enter the Advanced Test Reactor first for steady-state burn-up and then move to TREAT for transient testing, or follow a different path, has not been publicly detailed.
A fuel designed for heavy water reactors
Clean Core holds granted U.S. patent US11929183B2 and a related published application (US20220367071A1) covering thorium-based fuel bundle geometries engineered for pressurized heavy water reactors, or PHWRs. The designs describe how thorium and uranium can be distributed within fuel elements to balance reactivity, manage power peaking, and maintain compatibility with existing reactor hardware, all without requiring major modifications to the host plant.
That target reactor type is significant. PHWRs operate in Canada, India, Argentina, Romania, and South Korea, but the United States does not currently run any. The entire U.S. commercial fleet consists of pressurized water reactors and boiling water reactors, both light-water designs. If Clean Core’s fuel is intended primarily for export markets or for a future domestic heavy water design, the licensing jurisdiction and regulatory pathway will differ substantially from a program aimed at the existing U.S. fleet.
What is still unknown
Several important questions remain unanswered in publicly available documents. Clean Core has not disclosed a specific timeline for completing fabrication, shipping the rodlets to INL, or finishing the irradiation campaign. The categorical exclusion authorizes the work but does not bind the company to a schedule, so the gap between clearance and fuel insertion could stretch depending on funding, fabrication progress, and competition for national laboratory test slots.
There is also no published post-irradiation examination plan. After burn-up accumulation, fuel specimens typically undergo destructive and non-destructive analysis in hot cell facilities to measure fission gas release, pellet-cladding interaction, dimensional changes, and microstructural evolution. Whether INL’s Materials and Fuels Complex will handle that work, and which performance metrics will be prioritized, has not been stated.
The commercial and regulatory path beyond testing is equally open-ended. Heavy water reactor fuel incorporating thorium and low-enriched uranium would need to clear international safeguards reviews, nonproliferation assessments, and country-specific licensing rules in any market where it is deployed. None of the current public records indicate whether Clean Core has engaged regulators beyond the DOE environmental determination, or whether utility partners have been identified for eventual deployment.
A real step, with a long road ahead
The DOE categorical exclusion is a binding federal action, not a press release or a corporate aspiration. It confirms that a specific test program with defined fuel compositions and specimen counts has passed environmental review and can proceed. That makes the ANEEL-Fuel campaign one of the most concrete advances in U.S. thorium fuel development in a generation.
But authorization is not the same as completion. Fabricating ceramic nuclear fuel pellets to specification, irradiating them under controlled conditions, and then analyzing the results is a process that typically spans years. And even favorable irradiation data would be only the beginning of a licensing effort that must satisfy regulators in whichever country the fuel is ultimately deployed.
For now, the verified facts anchor this story in a real test program at real facilities. The unanswered questions, from timelines to target markets to regulatory strategy, will determine whether thorium fuel moves from the laboratory to the grid.
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*This article was researched with the help of AI, with human editors creating the final content.
