You might have learned about nuclear fusion in high school science class; it's the energy-releasing reaction that powers the sun. For a long time, scientists have worked to harness nuclear fusion as an essentially limitless energy source. The hope is to create sustainable nuclear fusion plants around the globe, making polluting dirty energy a thing of the past.
While it sounds like a stellar idea, there are a lot of hurdles to making the theoretical concept a reality. But a new startup has a promising potential solution to one of nuclear fusion's biggest commercial barriers.
Marathon Fusion is refining a process that purifies tritium, a rare hydrogen isotope essential for most nuclear fusion concepts. Fusion reactors generally run on tritium and another hydrogen isotope, deuterium. While deuterium is abundantly found in seawater, tritium is exceedingly rare. And you can't have nuclear fusion without the isotopes needed to cause the reaction.
"There's only 20 kilograms [about 44 pounds] of tritium anywhere in the world right now," Kyle Schiller, CEO of Marathon Fusion, told TechCrunch.
The news outlet reported that the current global supply of tritium is created as a waste byproduct of nuclear plants running on fission, which splits a heavy element with a high atomic mass number into fragments. To date, there are only about 440 nuclear fission reactors around the world, providing about 9% of the planet's electricity, according to the World Nuclear Association.
To merely start operations, a single fusion power plant would likely require a few kilograms of tritium — then it would have to produce more tritium to both power itself and future reactors, as TechCrunch explained.
"Deployment of fusion devices is this doubling process," Adam Rutkowski, Marathon Fusion's chief technology officer, said in the TechCrunch report. "You're breeding enough tritium to maintain the steady state consumption by the device, but you also need to breed excess tritium to start up the next reactor."
To help with this "doubling process," Marathon Fusion is working to refine the capabilities of superpermeation, a roughly 40-year-old technology that uses solid metal to filter impurities from hydrogen. The startup hopes to use the process to filter out tritium for use in fusion reactions.
To understand how this all works, it's helpful to have a basic understanding of nuclear fusion.
Per the U.S. Department of Energy, nuclear fusion occurs when "two light nuclei merge to form a single heavier nucleus." Fusion happens when — in a common example — tritium and deuterium merge to form helium, as the International Atomic Energy Agency explains. The reaction releases energy because the total mass of the helium nucleus is less than the mass of the two original lighter nuclei. In this process, a single neutron is also released — and that single neutron is key to creating more tritium.
As TechCrunch explained, to create more tritium in a fusion reactor, neutrons released during fusion will strike "a blanket of lithium," with the impact releasing more helium and tritium. Some of this created tritium will be injected back into the reactor to cause more nuclear reactions while the rest will be reserved as fuel starting other reactors. But before this can happen, the tritium needs to be filtered out from the reactor.
Existing equipment can do this filtering but only for experimental work. Running a reactor for a longer period of time on a commercial scale requires much more finesse. To make that commercial-level refinement a reality, Marathon Fusion is banking on superpermeation.
In overly simplified terms, superpermeation turns hydrogen and everything else needing filtering into a plasma. That plasma is then pressed up against a metal membrane, per TechCrunch, which allows only the hydrogen — including tritium — to pass through while blocking everything else. The result: Tritium is created and isolated for further fusion reactions.
Marathon Fusion has received early support from the Department of Energy and the Breakthrough Energy Fellows program. Now going public with its work, Marathon Fusion recently raised a $5.9 million seed round, the company exclusively told TechCrunch.
While all of this may sound promising, there are still barriers to harnessing nuclear fusion for limitless power. A lot of the process is currently still theoretical, working in labs in the short term but not viable in the long term commercially.
That's because current projects currently take more power to run than they create, requiring a huge amount of heat and pressure to cause a reaction. Only a few fusion projects have ever hit "breakeven," creating as much power as the process needs to run — or very limited and brief "ignition," outputting more energy than was put in to start the process.
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