Fusion Energy's Secret Achilles Heel May Have Been Solved
Fusion Energy's Secret Achilles Heel May Have Been Solved
The tritium problem could soon be a thing of the past.
Fusion seems like the ideal energy source. Theoretically, it can deliver copious amounts of on-demand energy with zero emissions, zero toxic waste and practically no nuclear waste. Its fuel is also so energy-dense that just a few tonnes can power an entire country for a year. But there is no such thing as a free lunch. Creating a fusion reactor that produces more energy than it consumes has been an engineering nightmare, yet we are tantalisingly close to solving this problem. However, even if we solve this monumental problem, fusion will still be unreachable, as a crucial component of its fuel known as tritium is so rare and so difficult to make that it currently costs around $30,000 per gram! This is fusion’s untalked-about Achilles Heel, but we may be on the brink of solving this too.
As always when talking about fusion, let’s quickly recap what it is and why tritium is so important.
Nuclear fusion is the process that powers the stars. The temperatures and pressures in their core are so high that hydrogen atoms have enough kinetic energy to overcome the repulsive force that keeps atoms separate. So, when two hydrogen atoms collide in this super-hot, super-dense plasma, they fuse to form helium. But this helium is slightly lighter than the two atoms of hydrogen it came from. This spare mass is transformed into energy and released. Einstein’s famous E=MC² states that a little bit of mass is equal to a vast amount of energy. This means that if you fuse a tiny amount of hydrogen, a truly immense amount of energy is released! To give you a sense of scale here, if you fused 17 tonnes of hydrogen, it would produce enough energy to power the entire US for a year!
However, different isotopes (different types of the same chemical element with different numbers of neutrons) of hydrogen fuse at different kinetic energy levels and release different amounts of energy in different forms. The most efficient fusion (lowest energy to fuse with most released energy) is between deuterium (hydrogen with one neutron) and tritium (hydrogen with two neutrons). As such, almost every single fusion reactor on Earth is specifically designed to work with these two isotopes and can’t function without either.
This is where the problem lies.
Deuterium is super stable, relatively common, and can be easily refined from normal water using chemical methods. Tritium, on the other hand, is unstable and has a half-life of 12.33 years, and as such, is practically non-existent in nature and has to be painstakingly artificially made. The most common and, so far, most productive way we have found to produce tritium is to irradiate an isotope of lithium known as lithium-6 in nuclear reactors. This creates a decay chain that eventually produces a tiny amount of tritium gas, which is then extracted from the nuclear reactor. This is an incredibly arduous task, hence the $30,000 per gram price tag, and why there are only a few kilograms of this stuff currently on Earth.
With tritium’s high price and severely limited supply, even if we created the perfect fusion reactor tomorrow, fusion energy simply couldn’t be a viable energy solution. What’s mind-blowing is that we are currently pouring billions of dollars per year into developing fusion reactors, but basically nothing into solving this crucial problem.
But a startup called Marathon is trying to change that. They are developing a technology that would enable fusion reactors to “breed” their own tritium supply and become self-sufficient.
Fusion reactors produce the same neutron radiation needed to turn lithium-6 into tritium. In fact, they produce far more of it than any fission nuclear reactor, as deuterium-tritium fusion reactions release most of their energy as neutron radiation.
As such, Marathon is developing a technology that surrounds the reactor with blankets of lithium-6 and uses this radiation to produce more tritium than the reactor uses to run. This idea is not new, and indeed, many fusion projects talk about doing this. However, no one has actually taken this idea off the drawing board, which is what Marathon is trying to do.
Part of the reason no one is actively developing this technology is that current fusion reactors only run in short bursts, so there isn’t enough time for these blankets to be properly irradiated and produce significant amounts of tritium. On the other hand, next-gen reactors like ITER should be able to run for long enough. But there are also other issues. How do you extract said tritium and inject it into the hyper-dense plasma at the reactor’s core without using a massive amount of energy? What’s more, as deuterium-tritium reactions release all of their energy in the form of neutron radiation, using this radiation to produce tritium makes the reactor less efficient, leaving less available energy for the fusion to self-sustain itself or to be extracted. As efficiency is the main hurdle for fusion reactors, this is a major issue.
So, how is Marathon planning to solve these issues?
Well, they intend to use a 40-year-old technology known as superpermeation that uses solid metal to filter impurities from hydrogen. You see, as hydrogen is the smallest atom around, it can pass through materials that other elements can’t. As such, a solid metal filter can let through only hydrogen, and as the only form of hydrogen these irradiated lithium-6 blankets will produce is tritium, this makes them perfect for quickly and efficiently refining said tritium. But, as a neat bonus, the process of superpermeation also massively compresses the hydrogen, giving it the pressure needed to be injected into the hyper-dense plasma in the reactor. As such, these metal filters act as a nearly completely passive system to refine tritium and inject it into the reactor, which saves a dramatic amount of energy compared to the currently proposed systems.
This doesn’t completely solve the energy usage issue, as it uses neutron radiation that could have gone to energy production or to sustain fusion. That being said, reactors like ITER are predicted to produce ten times the energy it takes to run, so the energy savings Marathon are already looking at could be enough.
So, that is how Marathon is looking to solve one of fusion energy’s biggest problems. What’s more, as they already have letters of intent from giants of the fusion industry, such as Helion and Commonwealth Fusion, they seem on track to develop their technology into a feasible solution and keep our fusion dreams alive.
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Sources: Will Lockett, The Cooldown, Tech Crunch, Marathon Fusion