Proponents of nuclear fusion have long promised to create nearly unlimited energy here on Earth by harnessing the same reaction that powers the Sun. Today, the biggest obstacle to fusion is ensuring that any fusion power plant produces more energy than it needs to operate. The second is to make sure it has enough fuel to run.
Many fusion reactors are designed to run on a mixture of two isotopes of hydrogen, deuterium and tritium. (Ordinary hydrogen atoms have no neutrons; deuterium atoms have one and tritium two.) There is plenty of deuterium found in seawater, but not nearly enough tritium, which is so rare that it essentially has to be manufactured.
“Currently, there is only 20 kilograms of tritium anywhere in the world,” Kyle Schiller, CEO of Marathon Fusion, told TechCrunch. A single commercial power plant will require a few kilograms to run, meaning the world has enough tritium for a dozen at most. His low-key startup thinks it has a solution to this problem.
Today, the world’s tritium supply is a waste byproduct of a small number of nuclear power plants operating on fission, a type of nuclear power that has been used for energy since the mid-20th century. Assuming scientists can use nuclear fusion to create viable energy on Earth, the first fusion power plants will tap into this supply. Future reactors will depend on the first crop of fusion power plants to be designed to produce additional fuel.
“The deployment of fusion devices is this doubling process,” said Adam Rutkowski, Marathon’s chief technology officer. “You grow enough tritium to keep the device’s consumption steady, but you also need to grow excess tritium to start the next reactor.”
This multiplication occurs when the neutrons released during fusion hit the lithium blanket. The impact will release helium and tritium and these products will then be removed from the reactor core where they can be filtered. Part of the tritium will be injected back into the reactor, while another part will be reserved as fuel for other reactors.
There is existing equipment for this task, but it is only useful for experimental work. It is efficient and effective, but because experimental reactors run for short periods of time, it does not have the throughput needed for a commercial power plant. To get to that point, filtration systems will need “several orders of magnitude of improvement,” Schiller said.
That’s where Marathon hopes to come in. He is working to perfect a 40-year-old technology known as superpermeation, which uses solid metal to filter impurities from hydrogen.
Here’s how it works: Hydrogen and other substances that need to be filtered out are first transformed into plasma, although not as hot as inside the reactor. Using pressure from the reactor exhaust, it is pressed against a metal membrane that allows hydrogen (including tritium) to pass through and blocks everything else. The membrane also compresses the hydrogen on the other side, which is a handy side benefit.
“The whole idea here is just to get the maximum throughput as quickly as possible,” Rutkowski said.
Rutkowski and Schiller have been working on this problem for several years and received early support from the Department of Energy’s ARPA-E program and the Breakthrough Energy Fellows program. Marathon recently raised a $5.9 million seed round, the company told TechCrunch exclusively. The round was led by 1517 Fund and Anglo American with participation from Übermorgen Ventures, Shared Future Fund and Malcolm Handley.
Marathon said it has letters of intent from both Commonwealth Fusion Systems and Helion Energy, two fusion startups that have raised $2 billion and $607 million, respectively.
Given that commercial fusion power is still several years away—if it’s even possible—Marathon’s bet may seem a bit early. After all, only one fusion experiment has reached a breakthrough in the scientific sense, which reduces the overhead of the equipment, which a commercial power plant cannot do.
Schiller disagrees that his company is too far ahead. “For the past ten years or so, we have been constantly surprised by how fast progress is being made [with fusion] he left,” he said. “I really think that when we wake up one morning and we’re on the edge of balance, we’re going to wish we’d started even earlier.”