Marathon Fusion enriches lithium and hydrogen isotopes in one centrifuge

Marathon Fusion’s plasma-centrifuge programme targets isotope-separation challenges in the fusion fuel cycle

(Image courtesy of Marathon Fusion)

Lithium and hydrogen isotopes have been enriched in a single plasma centrifuge, a demonstration aimed at two of the toughest bottlenecks in the fusion fuel cycle. Tritium must be recycled fast enough to sustain a burning plasma, and lithium-6 must be produced at scale to breed replacement fuel. The two results, however, carry different levels of outside verification.

A plasma centrifuge for fusion isotope enrichment

Behind both results is a single piece of hardware, built to support a process called differential pumping. Marathon Fusion says this could eventually cut tritium flow rates, and shrink the processing systems built around them, by a factor of ten or more, though that figure describes the technology’s objective rather than a result achieved so far. The Department of Energy named tritium processing a core challenge in its Fusion Science and Technology Roadmap, published in June. Marathon’s work is backed by the DOE’s ARPA-E VISION OPEN programme, and the company describes itself as one of three private fusion firms receiving that support. Of the two isotopes involved, lithium carries the bigger supply problem.

Plasma centrifuge separation closes a lithium supply chain gap

A fusion supply chain report from the Special Competitive Studies Project named lithium enrichment the industry’s highest-risk gap, noting there is “no domestic commercial supply.” Lithium-6 is the isotope needed to breed tritium inside a reactor blanket, most commonly using the molten salt FLiBe. UC Berkeley nuclear engineering professor and Marathon adviser Per F. Peterson said the world currently produces less than a tonne of enriched lithium a year, using a mercury-based process now limited to Russia and China. Reaching terawatt-scale fusion deployment, he said, would require hundreds of thousands of tonnes of enriched lithium in service. On Peterson’s account, no clean production route currently exists at that scale. Whether Marathon can help close that gap depends partly on what’s actually confirmed so far.

What outside labs have confirmed so far

The two results announced this week sit at different stages of outside scrutiny. Testing lab Covalent has independently confirmed the lithium-6 enrichment, Heatmap News reported after speaking with the company. The hydrogen separation result hasn’t gone through that same external check yet, although an MIT nuclear engineering professor has looked over the device’s design. Marathon also hasn’t run the process on real tritium so far. Instead, the company is proving out its separation physics with deuterium and protium, two isotopes that behave similarly to tritium without the cost, radioactivity, or Nuclear Regulatory Commission oversight that handling actual tritium would involve.

Marathon eyes a commercial pilot and a Series A

That work now moves toward a commercial pilot facility, with the company pursuing a Series A round off the back of these results, according to Heatmap News. Its 2029 target for full-scale production would put annual lithium-6 output in the tens of tons, a volume the company says could supply a new gigawatt-scale fusion plant roughly every two years. Alongside that, Marathon is aiming to recover and reuse something in the region of 560 kilograms of tritium a year, broadly matching the throughput of a single one-gigawatt reactor’s fuel system. Those numbers describe where Marathon wants to get to, not what this week’s lab demonstration has actually shown.

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