Fusion energy, the future, or a waste of time?
An intro to fusion and how it works
Everyone knows the effect of burning fossil fuels, and what it does to the atmosphere. Scientists have come up with renewable energy sources like solar panels, hydroelectricity, wind turbines, etc. While these solutions are all great, they are currently too inefficient to power the whole globe. Fusion energy, the process of fusing nuclei and releasing energy, has stayed mostly in the shadows up until now. Fusion is how the sun and all other stars produce energy. Scientists hope to harness that power to create a nearly limitless source of energy, with little to no pollution. For fusion to occur, it has to be hot enough that atoms (normally hydrogen) lose their electrons, creating a plasma where nuclei and electrons move freely. Nuclei have a positive charge and naturally repel each other, to overcome this. They have to be moving very, very fast. That means temperatures in the millions of degrees. The nuclei are then forced to fuse, creating heavier nuclei (helium) and releasing energy in the process. This process is quite easy in the sun as it’s own mass causes the pressure in their cores to heat up enough to cause the reaction to happen. On Earth though, that’s not feasible.
Fusion on Earth
Currently, there are two ways scientists have replicated fusion. Magnetic confinement reactors, and inertial confinement reactors. But we can’t just use regular hydrogen like the sun. Special isotopes of hydrogen with more neutrons are needed to make the correct reactions happen. One of these isotopes, deuterium is stable and abundant in seawater. While the other tritium is radioactive and hard to find.
Magnetic confinement reactors
To understand how these machines work, we have to take a look at the parts that make them up. Magnetic confinement reactors are housed in a donut-like shape of stainless steel as a layer of protection. The so-called “ lithium blankets”, protect the housing from the extreme temperatures needed for fusion. Superconductive magnets are then placed around the entire housing, these magnets are the key part of the reactor, (hence the name). A cryostat helps keep the magnets cool, and the environment like a vacuum. Now we can truly understand how they function. The power needed to start the reaction will be around 70 megawatts and fusion will yield around 500 megawatts. The reaction can take anywhere between 300–500 seconds.
- The reactor heats deuterium and tritium into high-temperature plasma
- The magnets squeeze the plasma for fusion to occur
- The lithium blankets absorb the high energy neutrons produced by fusion to start producing more tritium fuel, they also become hot.
- A water cooling loop will transfer the heat to a heat exchanger to produce steam. The steam then turns the electrical turbines to produce electricity.
- The steam is cooled by the cryostat and condenses back into water, which is then taken back near the blankets to repeat the process.
A great example of a magnetic confinement reactor is the ITER project. This is an international effort by countries including the U.S, Russia, Japan, and India. Back in 1988, President Ronald Reagan and Russian Prime Minister Mikhail Gorbachev agreed that no one country could come up with a solution to fusion energy on their own, so they agreed to collaborate on the project which came to be known as ITER. More than 30 years and 24 billion dollars later, the reactor was starting to be built earlier this July! If everything goes to schedule, the reactor should power on for the first time in 2025.
Inertial confinement reactors
The second type of fusion reactors, inertial confinement reactors use high power lasers giving off pulses onto a fuel pellet. The pellet then implodes, and for a short amount of time, it’s hot and dense enough for fusion to occur. Some of the world’s most powerful lasers are used for fusion experiments like this one. At the National Ignition Facility in the U.S, 192 laser beams are pointed at a target cylinder called a hohlraum. At the center of the hohlraum will be a pea-sized pellet of deuterium and tritium.
- The lasers will heat the cylinder, producing x-rays.
- The heat and radiation will compress the pellet and turn it into plasma, allowing for fusion to occur.
- Water again will be heated and turned into steam to produce electricity.
The fusion reaction is very short, only lasting about one-millionth of a second, but it yields 50–100 times more energy than is needed to start the process. Scientists also estimate that each pellet only costs 0.25$ to produce, making this method very cost-efficient. If this were to be more commercially viable, there would probably be multiple pellets inside the cylinder to provide a more sustained reaction.
Problems with fusion
Up to this point, fusion sounds like a perfect source of energy. You’re probably thinking why the world hasn’t already made the switch. Simply put, it’s because fusion is still not commercially viable. High operating costs, radioactive waste produced by the process, and radiation damage to structures, are just some of the reasons why fusion reactors can’t be rolled out worldwide as of now. Lets first cover the problem with tritium. Tritium is extremely rare to find naturally, as it’s radioactive and has a half-life of only 12.3 years. The main way we obtain tritium is from fission nuclear reactors, where tritium is a byproduct of the process. Because of the lack of tritium, the reactor itself must produce some. In magnetic confinement reactors, the lithium blankets as mentioned above, produce tritium. This happens when the blankets are heated and exposed to radiation. They “breed tritium”. Unfortunately, the lithium blankets still do not produce enough tritium to fuel the reactor continuously, meaning that unless we found another isotope of hydrogen or another molecule, we would be dependent on nuclear fission reactors to supply us with tritium. Fission reactors produce radioactive waste that takes millions of years to biodegrade. While the fusion reaction itself may produce more energy than it took to start the reaction, they will still not produce enough electricity to cover the costs. Even when the reactor is off, you still need electricity for the cooling systems, the ventilation, and tritium processing to name a few. In inertial confinement reactors, you have to recharge energy storage systems between each pulse of the lasers so they can fire again. This can consume anywhere between 75–100 megawatts continuously. The fusion reactor needs to produce over 1000 megawatts of electricity (which it can’t currently do) just to break even. On top of that, high energy neutrons produced by fusion are radioactive and damage structures. These are some of the problems which plague fusion reactors from becoming our main source of energy.
Possible Solutions
Let’s first address the tritium and radiation damage. A company called TAE Technologies is currently working on trying to replace tritium with boron 11, an isotope of boron. This possible solution would completely take out the need for tritium and the dependency on nuclear fission reactors. Unfortunately, we have no solution to the electrical consumption of reactors as of now.
A conclusion
Fusion energy holds an ungraspable amount of potential. If we want to move forward as a civilization, at one point or the other, we have to make the switch to fusion. But as of now, it’s filled with problems that at this point have no solution. These things have caused fusion to coined as being “always 30 years away”, and some have even called for research to be stopped claiming it will never be commercially viable. While there has always been a sort of idealism towards fusion, until we find a source of renewable energy that is as effective, in my opinion, we should keep searching for ways to bring costs down.
Sources:
A great intro video to fusion
An article that showcases the downsides of fusion
The ITER website (would definitely check this out if you’re interested in learning more about fusion)
The National Ignition Facilities website, they conduct experiments using inertial confinement reactors
https://wci.llnl.gov/facilities/nif
http://www.nuc.berkeley.edu/thyd/icf/IFE.html
