How we Can Fix Nuclear Fusion – Well, Part of It
Energy is our most valuable currency. Everything we do is fuelled by it.
It powers our homes. It allows cars and buses to be driven. It provides light. It’s the reason you can read this article right now.
The problem is, not everyone gets energy. In fact, 1.2 billion people live in energy poverty. This means that they have little or no access to electricity. That’s 16% OF THE ENTIRE WORLD!!!! 😱
🤔 How can we give energy access to everyone in a clean, long-lasting way?
Nuclear fusion is a buzz word in the world of energy that’s always coming up. We’re always told that ‘iT’s OnLy tWeNty yEaRs aWaY”, when in reality, that’s what the saying has been 60 years. There are a lot of problems with it preventing it’s development, but, if unlocked, it has huge potential.
Backtrack… What is nuclear fusion?
To put it simply, we’re taking tiny atoms to create BIG energy 💥
To make it a little bit more specific, we are taking two or more light atomic nuclei and combining them to make one heavier atomic nucleus, creating large releases of energy.
This works because the mass of the combination of these two nuclei is less than the sum of the masses of the individual nuclei.
The sun does this every day. The conditions and gravitational pull are perfect for creating such reactions, but, on Earth, fusion is pretty dang difficult to achieve 😕
1. Two pairs of protons fuse, forming two deuterons
2. Each deuteron fuses with an additional proton to form helium-3
3. Two helium-3 nuclei fuse to create beryllium-6, but this is unstable and disintegrates into two protons and a helium-4
4. The reaction also releases two neutrinos, two positrons and gamma rays.
In order for nuclear fusion to work, we need to use fuel. Right now scientists are looking at two main options: Deuterium — Deuterium or Deuterium-Tritium.
Hint: One’s better than the other… but, I’ll get to that in just a bit 😉
Deuterium a stable isotope of hydrogen with a mass that is around twice that of the usual isotope.
There are four main reactions that come alongside deuterium, and these events are known as the deuterium cycle. All fusion reactions with deuterium fuel must stem from these components. They all have different byproducts.
Deuterium — Tritium Reactions
Now, we’re going to introduce another friend into the equation… quite literally…
Tritium is an extremely rare isotope of hydrogen, containing one proton and two neutrons. In nature, it’s only found when a gas and cosmic ray interact, so we have to generate it artificially on Earth.
This can be done through Lithium-breeding or by following the reactions of the deuterium cycle (meaning that you need to undergo fission in order to generate tritium).
A Deuterium-Tritium reaction is the most powerful of the deuterium cycle’s reactions, yielding around 17.6 MeV of energy.
Note: This doesn’t guarantee fusion. We can’t even dream of fusion until the Coulomb barrier is beat, which requires SUPER high temperatures. However, it is much easier to break this barrier with a D-T reaction over a D-D reaction, more on this in just a bit 😉.
Deuterium — Deuterium Reactions
Hydrogen is one of the most abundant elements on Earth. This means that Deuterium-Deuterium fuel could virtually always be available.
This type of fuel divides its output energy between neutrons and protons. The proton fraction interacts with a medium through electromagnetic force, converting kinetic energy to thermal energy very quickly. However, it requires slightly more energy than the D-T reaction.
The first byproduct of the reaction does not produce neutrons, but it does produce tritium. Just because a D-D reactor doesn’t need a tritium input, doesn’t mean it won’t involve tritium at all 🤯. But, there won’t be any leftover tritium. Unless the tritons can be quickly removed, most of the tritium produced would be burned before leaving the reactor, reducing the amount of tritium required for handling.
*The thing is, this would produce more neutrons, some of which are very energetic and just love zooming around 🏃♀️, which can lead to problems.
The neutron from the second branch has an energy of only 2.45 MeV. For comparison, the neutron from the D-T reaction has an energy of 14.1 MeV. The removed tritium decays to 3He with a 12.5 year half life. By reusing this materiral from the tritium byproduct and inputing that into the reactor, the fusion reactor can avoid materials resistant to speedy 14.1 MeV neutrons.
If the tritium in a D-D cycle can completely burn up, we can assume that the fusion energy carried by electrons would only be around 18%, meaning tritium breeding (monitoring and using the tritium) is not required.
Here’s the catch.
The energy confinement time (at a given pressure) of a D-D reaction must be 30 times longer and the power produced (at a given pressure and volume) would be 68 times less than the D-T reaction. The temperatures also need to be much higher in order to achieve the same results 🤦♀️.
There are also two main types of nuclear fusion, which we should also understand; Inertial and Magnetic confinement. I’ll be highlighting D-T reactions when explaining these branches of confinement.
Inertial Confinement
Inertial confinement focuses on applying a monumental amount of energy to a minuscule pellet of D-T and allowing it to implode until fusion is achieved.
Step One (See diagram below): This process starts off by symmetrically applying energy to the surface of a fuel pellet (containing the deuterium and tritium gas) that is surrounded by a thin coating containing ‘heavy’ atoms.
Step Two: The heat and pressure from this event result in the vaporization of the outer layer, blasting outwards.
Step Three: The reaction forces form shockwaves that travel inwardly, allowing for the implosion of the pellet as a result of the compression of its core.
Step Four: Finally, the pellet undergoes fusion, leading to the release of thermonuclear heat. Ignition occurs as a result of heat travelling from the inward layers outwards.
Right now, we have two main methods of applying this energy onto a fuel pellet: direct drive and indirect drive.
Direct drive applies energy directly to the pellet via lasers. It’s generally more efficient than indirect drive but there are other problems that come up because of asymettry.
Indirect drive suspends the pellet in this wacky device called heated hohlraum. It’s a cylindrical container typically made of gold. However, this method doesn’t have the highest levels of efficiency because incident energy is constantly being absorbed and fractionally transmitted.
Magnetic Confinement
Magnetic confinements takes large amounts of D-T plasma with a density of less than a milligram per cubic metre and confines it to a magnetic field. The atmosphere allows heat and pressure to produce a fusion temperature.
This seems to be the most promising method because the magnetic fields can confine plasma. The electrical charges on separated ions and electrons hace this ability to follow magnetic field lines, so it’s not as difficult to prevent electrons from entering reactor walls 🎉.
The current approach to magnetic confinement is taking donut-shaped (the proper term for this is torodial-based) magnetic configurations, such as a tokamak or stellerator and superimposing polodial fields (magnetic fields). This allows plasma to be confined and controlled.
There’s a Catch — Tritium is Hard (and Expensive) to Replenish
At this point in time, the equal mixture of deuterium and tritium may be the only feasible fusion fuel. Deuterium is readily available, and easily found water but, tritium solely exists in ultra rare scenarios. And just to make fusion even harder to achieve, the half life of the tritium isotope is radioactive with a really short half life 😳. As a result of this, the main way that we can generate tritium is through fission nuclear reactors.
🔑 The tritium fuel must be generated by the reactor itself
Tritium is really, really rare. This means we have to find a way to sustain these reactions as long as we can, and waste as little fuel as possible.
In theory, tritium consumed can be fully regenerated, however, in order to accomplish this goal, we need to place a lithium-containing blanket around the reacting medium, an extremely hot, ionized gas known as plasma. Neutrons produced from the fusion reaction can irradiate lithium, resulting in tritium breeding.
However, there’s a huge problem with this:
The lithium blanket cannot fully surround the reactor, because there need to be gaps for vacuum pumping, beam and fuel injection in the magnetic confinement method. In inertial confinement, gaps need to be available for driver beams and removal of target debris. However, even without completely encapsulating the fusion blanket, there can be a 15 percent surplus of tritium. However, in real life, we will need to use that surplus to help with the processing and incomplete extraction of the tritium being bred in the blanket.
While we can replace the burned up fuel, we can’t actually replenish the fuel supply. Less than 10 percent of the injected fuel will actually be burned in a magnetic confinement fusion device before it escapes the reacting region. Most of the tritium needs to be scraped from the surface and interior of the reactor around 10–20 times before it is completely burned.
If just 1% of the unburned tritium cannot be recovered and re-injected, than no matter how large the surplus from the lithium-blanket is, the lost tritium cannot be made up.
In the two magnetic confinement facilities where tritium has been used (Joint Europe Torus and Princeton’s Tokamak Fusion Test reactor), around 10% of the injected tritium was never recovered: a major, major, loss. 😬
Right now, in order to make up the unburned tritium losses, fission reactors need to be used in order to produce a sufficient supply, which have a bunch of safety and nuclear-non proliferation problems that come alongside them 😡.
Without making changes to the lithium blanket, we can assume that deuterium-deuterium reactions would be the only feasible ones.
But what if we were able to integrate something else into the blanket to make it more efficient?
By amalgamating the lithium blanket with a heavy isotope of oxygen, known as Oxygen-18, it may be possible to create a stronger blanket that is able to retain oxygen more efficiently.
Why the Heavy Blanket?
It’s easy for tritium fuel to escape when the Lithium blanket has holes and is so light, and if we still need the spaces, one way to fix this problem is to make the blanket heavier, and force more pressure on the tritium to stay inside the reactor.
Oxygen is a non-metal, which means that’s it’s going to be attracted to metals like Lithium. Oxygen is a diatonic element, meaning when left alone, it known as 02. This means that in order to create Lithium Oxide (Li20), we would need to have two lithium (Li) atoms for every one oxygen (O) atom.
In real life, this would work out to have a ratio of 2x the amount or weight or Lithium to the weight of oxygen.
But… It’s not that simple
There are a lot of other factors that we need to take consider in order to go through with researching Lithium Oxide blankets.
- ‘Recess’ contribution is excess unusable tritium or other byproduct generated in the thinner regions of the blanket. How we can avoid this and focus on usable tritium?
- There are certain regions of the fusion plant that cannot be covered, such as the pumping duct entrance region. How do we accommodate these needs while still allowing for proper coverage? This factors causes the fusion power and burn times to vary a lot.
- How can we remove heat from the TFC (toroidal field coil)? What about heat from other sensitive parts?
Now, this isn’t something that’s confirmed to work right now, but, neither is a lot of fusion techniques that are circulating today. Research needs to be done into the topic, and if proven to work, we can overcome some of the obstacles that we face with making fusion work.
THAT’S LITERALLY FREAKING CRAZY 🤩
It has potential, but, I’m not going to say that it’s going to change the world as we know it. Right now, this approach to fusion is just an idea, but, maybe, it’s an idea worth considering.
🔑 Key Takeaways
- Nuclear fusion is using small atoms to create large amounts of energy, by trying to mimic the reactions that happen on the sun ☀️
- There are two types of fusion fuel: Deuterium-Deuterium and Deuterium-Tritium. Deuterium-Tritium is much more efficient but Deuterium-Deuterium is more feasible as of right now ⛽️
- There are two primary approaches to fusion: Inertial and Magnetic Confinement, which also have their own pros and cons 💡
- Tritium is really hard to create, and is mainly generated through fission. We need to maintain and generate as much as we can ⚡️
- Using Lithium blankets can help store and create surplus of tritium, however, the current method is really inefficient 😔
- Strengthening the Lithium blanket by amalgamating it with a heavy isotope of oxygen-18 could make it more efficient, but this is still an idea 💪
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