Absent this firm’s innovation, prospective fusion reactors could remain unilluminated

Advocates for nuclear fusion have always envisioned a world with an abundant supply of energy, mimicking the sun’s power-generating mechanisms right here on Earth. The primary challenge in achieving this dream is developing a fusion reactor that generates more energy than it consumes. Additionally, securing a sufficient fuel supply remains a pivotal concern.

A key element in many fusion energy designs is the utilization of two hydrogen isotopes, deuterium and tritium, as fuel. Unlike ordinary hydrogen, which has no neutrons, deuterium atoms contain one neutron, and tritium atoms have two. Ocean water offers an ample supply of deuterium, whereas tritium is exceedingly scarce and must essentially be synthesized.

“Currently, the world’s total tritium inventory is about 20 kilograms,” Kyle Schiller, CEO of Marathon Fusion, shared with TechCrunch. Considering that launching a commercial-scale reactor requires a few kilograms of tritium, there’s only enough for a very limited number of plants globally. Marathon Fusion believes it has crafted a solution to this challenge.

At this moment, the global tritium supply is derived as a by-product from a handful of nuclear fission reactors — a different approach to nuclear energy that has been utilized since the mid-20th century. Should fusion energy become a practical reality, the initial generation of fusion reactors will rely on this tritium. Subsequent generations of reactors will be expected to produce additional tritium, sustaining and expanding the available fuel supply.

Adam Rutkowski, Marathon’s CTO, explains, “Deploying fusion reactors involves a doubling process. It’s about breeding sufficient tritium to keep the reactor running, while also generating the excess needed to fuel the launch of subsequent reactors.”

This “breeding” occurs when neutrons produced by the fusion process interact with a blanket of lithium, yielding helium and tritium. These by-products are then siphoned off from the reactor core to be filtered and separated. Some tritium is recirculated into the reactor, with the rest earmarked for future fusion reactors.

Current technology can handle these tasks but is limited to laboratory applications due to its scalability limitations for commercial operation. Advancing these filtration systems by several orders of magnitude in efficiency is crucial, according to Schiller.

Marathon Fusion’s strategy involves optimizing a decades-old technique known as superpermeation, which efficiently filters hydrogen impurities using a solid metal membrane.

The process entails converting hydrogen into plasma (though not as intensely hot as that within the fusion reactor) and applying pressure from the reactor’s exhaust. This forces the plasma against a metallic membrane that selectively allows hydrogen, including tritium, to pass through, while blocking other elements and simultaneously compressing the hydrogen—a beneficial byproduct of this method.

“Our goal is to achieve the highest possible throughput speed,” Rutkowski emphasized.

Rutkowski and Schiller, supported initially by the Department of Energy’s ARPA-E program and the Breakthrough Energy Fellows program, have been navigating these challenges for several years. Recently, they successfully raised a $5.9 million seed investment, as exclusively reported to TechCrunch. The funding round witnessed participation from entities such as the 1517 Fund, Anglo American, Übermorgen Ventures, Shared Future Fund, and Malcolm Handley.

Despite the nascent stage of commercial fusion energy, which remains several years away and unproven, Marathon has secured letters of intent from major fusion energy startups Commonwealth Fusion Systems and Helion Energy, which have raised significant funds to date.

While critics may argue that Marathon is ahead of its time, given the current state of fusion energy research, Schiller remains optimistic. He reflects on the rapid progress within the fusion sector over recent years and believes starting early is essential. “Should we achieve a major breakthrough, reaching the point of energy breakeven, we’ll regret not beginning our efforts sooner,” he stated.