Introduction
Nuclear fission power is a non-renewable energy source that releases zero carbon dioxide into the atmosphere with high amounts of energy released for little amounts of fuel, however the brother of it, nuclear fusion is essentially fully sustainable, also releases zero carbon dioxide and produces more energy per gram of fuel. Is this not the perfect energy source then, solving global warming, worries about running out of fission fuel and able to fully replace fossil fuels?
Nuclear power and how it works
Nuclear power as we know it today is the nuclear fission of Uranium-235 or Plutonium-239 in some specialist reactors and releases a steady output of power contributing to around 10% of global energy production. Inside the reactor these large atoms split into two smaller nuclei, converting some mass into energy and releasing a large amount of energy for little amounts of fuel - 1g of U-235 yields the same amount of energy as the burning of around 3 tons of coal. However, scientists have always been more interested in nuclear fusion, the process fueling the sun, with it producing 3 to 4 times more energy per gram, often being overly optimistic with how far away fusion power plants are from being fully developed. You might hear people say “Nuclear fusion has been 10 years away for half a century now” as a classic quip against these fusion scientists. As you might have guessed, fusion is the opposite of fission; the fusing of two particles, converting some mass into massive amounts of energy.
Below is a graph of average binding energy per nucleon against number of nucleons
The reason why fusion releases more energy than fission is explained by the graph above. On the left side of the graph are the atoms that fuse. When they fuse, they move up the curve and that difference is the amount of energy released. Compared to fission on the right side of the curve, you can clearly see that fusion moves up the curve much more rapidly and hence releases more energy (put simply).
Advantages of Nuclear Fusion
As mentioned before, nuclear fusion releases more energy than nuclear fission with all the other advantages fission has as well. Fusion also uses deuterium and tritium for fuel, two isotopes of hydrogen. Deuterium is in mass abundance in the oceans and while tritium doesn't exist in nature, it is easily formed in fusion reactors when neutrons collide with lithium which is why fusion reactors have a lithium covering to create the tritium needed. Fusion also produces no nuclear waste, a radioactive by-product of nuclear fission that has to be treated extremely carefully to prevent damage to the environment and people. The only issue is the large amounts of neutrons produced that bombard the reactor walls, but this is easily solvable with the right material and protocols. Finally, fusion has essentially no chance of nuclear meltdown - an uncontrolled chain reaction like what happened at Chernobyl - due to the precise conditions needed to initiate fusion breaking down immediately once something goes wrong.
Disadvantages of Nuclear Fusion
There is really only one major issue with nuclear fusion; how hard it is to create the conditions needed to initiate fusion in a controlled and sustainable manner. Deuterium-tritium fusion requires around 100 million degrees celsius to begin to have any reasonable power output. Nuclear power often comes down to statistics: the goal is to get the chance of particles fusing or splitting to be high enough that the reaction stays at a constant rate but low enough that it doesn’t go out of control. To do this for fusion, you can either get the particles extremely close together so that there is a large chance they get close enough to fuse or you can make the particles go so fast that there are more opportunities for the particles to collide per unit time. In the sun, due to the massive gravitational force, the particles are packed extremely close together with massive pressure, meaning the particles have a massive chance to fuse together. On Earth, that pressure is not possible to achieve, so to make up for it fusion reactors have to be much hotter even than the core of the sun. The struggle with designing a commercially viable fusion reactor has been to get a sustained reaction to last at these extreme temperatures without melting the reactor itself as virtually nothing is solid at those temperatures. Therefore fusion reactors have to use massively strong magnetic fields to hold the fusion material in place. It's far easier to say how to do it than to achieve this which is why scientists have been struggling for so many years to finalise a commercial fusion reactor. And even when the design is finished, each fusion reactor will be ridiculously expensive, perhaps making governments shy away from actually building them.
So is fusion the “Holy Grail” of energy production?
On paper, certainly. It produces the most energy per gram of fuel, is carbon dioxide free, has almost inexhaustible amounts of fuel and is risk free. However, the incredible conditions needed in a fusion reactor have prevented a fusion reactor being commercially viable for three quarters of a century and even when we do solve these issues, the high upfront costs might mean we need to wait even longer to reduce these costs to finally implement fusion reactors fully. Fusion reactors, when properly finalised, will solve most of our energy related problems and help the world achieve carbon neutrality, but do we have the time to wait? I think not.
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