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I know you’ve seen lots of people say “fusion is limitless energy forever and it’s just around the corner. A brighter future will soon dawn for everyone.” I think that hype is maybe not ideal. I do this thing where I read the news like I’m watching lottery drawing – maybe today will be THE DAY and all the problems are SOLVED. I think that’s setting myself up for disappointment. Instead, I took a look at some technical problems and how far along researchers are to solving them.
Unlike renewables, fusion would provide baseload, on-demand energy. It doesn’t produce nuclear waste like nuclear fission. And it’s exciting! Like space exploration or fireworks, it’s just neat!
People have said fusion is 30 years away and it always will be. But I don’t think so. A lot of the problems HAVE been solved. Progress has been made. It’s not ready, but it’s still fun to look at that progress and the different solutions that clever people are trying.
Fusion didn’t have to take this long. I know it bothers some people to talk about politics, but look at this. This is a failure of vision. We need more. More science, more fusion, more research in general. Energy should have been a solved problem in 2005. We could be so much farther along, but we’re not because… scientists don’t have good lobbyists?
I digress. Stay hopeful. Nothing is as hope-sucking as politics.
This is about fusion fuel – and fusion fuel is potent. There’s enough fuel to run fusion forever if we can make it work. But there are lots of reasons why fusion is hard, and why it was always going to take a lot of money and effort to get it to work. It’s not like in the movies. In Spiderman 2, Doc Oc has to restrain the fusion reaction with his robo-arms. Fusion just is not that aggressive.
Fusion not like nuclear fission (bombs and existing power plants). In nuclear fission, a chain reaction produces heat and the challenge is to control it. Fission is like this dog that wants to run on this treadmill. It wants to GO.
Fusion more like trying to get a very lazy cat to run on a wheel.
It’s hard, but not impossible. It is definitely not just theoretical. Farnsworth fusors are straightforward enough that high school students have constructed them. A twelve-year-old kid (with very supportive parents) built one. Home-built fusion reactors use deuterium fuel which is naturally present in water. They produce energy primarily as neutrons, though, which is not ideal. Neutrons can activate the wall of the reactor, making it mildly radioactive.
To be a practical energy source, the reactor needs to use those neutrons to make steam, then electricity, then pay back the running costs of the reactor (which use a lot of power) and the energy cost of enriching the deuterium, and then the leftover can be sent to the grid. Deuterium fusion has never produced remotely enough energy to do that.
But there are other fuels.
The national ignition facility (NIF) has produced net energy from their reaction. One unit of energy in produces 2-3 units of energy out. That’s good! NIF is using a higher yield fuel called tritium.
This is still for research purposes. The NIF reactor is not suitable for steam production – it runs one shot at a time using these fuel pellets and doesn’t even try to collect the energy. The ITER is getting closer to a practical reactor. It is being constructed now as a research reactor designed to prove that a deuterium-tritium fusion reaction could be used to build a power plant (eventually).
The D-T reaction looks like this. Tritium is not natural, it’s synthetic only, and it decays. The half-life is about 12 years. It’s also quite radioactive. So, instead of explaining how this reaction works, I’m going to look at where the fuel comes from and how it differs from other power plant proposals.
D-T is the fuel of choice because it’s the easiest fusion reaction we know of. It requires the least energy input. After the fancy plasma reactor makes heat, the rest of the process is the same as any coal or nuclear power plant. Neutrons heat water to steam, a turbine makes electricity. The electricity is used to run the reactor, and there had better be enough left over to refine more deuterium. Then the rest can be sent to the grid. But that’s only half of the fuel. Where does the tritium come from? The good news is that you can use those neutrons to generate tritium. Tritium is in short supply, so this needs to be worked out as a practical problem for any D-T power plant.
But there are some startups that are trying to simplify all of that. Helion is one. They are making a smaller reactor that avoids tritium and neutrons and steam.
They use helium-3, the fuel at the center of that sci-fi movie, “Moon” (2009). Helium-3 is fairly abundant on the moon, but that’s not the most practical place to get your reactor fuel. Famously, the moon is hard to get to.
It has some real advantages, though. The Helion reactor fuses deuterium with He-3 to make He-4 and a proton. Unlike neutrons, those products comes out of the reaction as a high energy ion. Moving ions are basically already electricity. So, there’s no need for steam or turbines. That’s could make for a much simpler and cheaper power plant.
But you still have deuterium in the reactor, so you get some D-D side reactions, and those do produce neutrons. That’s a curse and a gift. On one hand, you have to deal with generating radioactive neutron activation products. On the other hand, you can use those neutrons to make helium-3, that rare fuel you can’t do without. Neutrons can cause lithium to split into tritium which decays into He-3… over the course of a few decades. That’s the proposed Helion fuel cycle.
But it can get even simpler. Tri-alpha energy is building a reactor that wants to get rid of all the neutrons.
This takes boron-11 and hits it with protons (natural, non-heavy hydrogen) and makes 3 helium ions. They convert those hot ions directly to electricity. It’s a once-through cycle, no neutrons or radioactive isotopes required. Unfortunately, this reaction is about ten times as hard to run.
I don’t know who is going to get there first. The NIF had the first net energy gain in 2022, so we’re really about at the Chicago Pile stage. If you saw Oppenheimer (and you should, it’s great), it was the scary graphite reactor under the football stadium. Going from that pile of uranium and graphite to a working power plant was a long haul. But we got there. And I think we can get there with fusion, too.
These startups with their fast time tables are what has me hitting refresh every day hoping for the big story. I’m a scientist, I’m in the trenches, and it rarely works like that. Most of the time it’s a gradual process, many iterations. But it’s fun to watch and speculate. Can you imagine neighborhoods powered by these reactors?
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Image Credits:
Comic made with Dall-E-3 and Firefly.
Fusion funding graph, originally from U.S. Energy Research and Development Administration Report ERDA-76/110 (1976). Color version from S.O. Dean (1998) http://dx.doi.org/10.1023/A:1021815909065
Deuterium-Tritium reaction diagram: Deuterium-tritium fusion.svg by Wykis, Public domain, via Wikimedia Commons
References:
“Fusion Power May Run out of Fuel before It Even Gets Started.” Accessed February 16, 2024. https://www.science.org/content/article/fusion-power-may-run-fuel-even-gets-started.
Dr. Peter B Allen - Lab Blog 
