Nuclear Fusion: how it could still be eco-friendly

Sometimes the science and maths we learn at school can seem unrelated to the real world, but one of the best parts of STEM is that it is constantly shaping the world and solving issues that affect us all. Nuclear fusion is just one example of an area currently being researched which has the potential to revolutionize the energy industry.

We are constantly looking for more sustainable alternatives to burning fossil fuels which would be able to keep up with worldwide energy demands. While there were hopes that greenhouse gas emissions would be greatly reduced as a result of Covid-19 lockdowns, the drop has not been as large as people had hoped and it is far from a sustainable solution. Although wind and solar energy are options, reports from BP and “Resources for the Future” have found that by 2040, these will only make up roughly 30% of global energy. While this is, of course, better than nothing, there is still a long way to go. Nuclear fusion is a promising opportunity, to which the government allocated £220 million in 2019.

Nuclear fusion is different to nuclear fission (the process used in nuclear power plants today) and is considered safer. Essentially, nuclear fission involves splitting atomic nuclei, while fusion (the process powering the sun) combines smaller atomic nuclei to form heavier nuclei. Both processes release huge amounts of energy due to the decrease in mass between the products and the reactants. Einstein’s famous equation E=mc2 illustrates how mass and energy are intrinsically linked and in fusion and fission, the products of the reaction weigh less than the reactants. This mass has not been lost; it has been converted to energy.

An advantage of fusion over fission is that there is no risk of a radioactive meltdown, since if it goes wrong, instead of a runaway reaction, fusion simply does not produce any energy. Fear of radioactive meltdown is a major reason for the reluctance to build more nuclear power plants, and that is why fusion could provide a better alternative. Additionally, while both processes produce radioactive waste, fusion produces less waste, and the waste that is produced has a much shorter half-life.

Fusion is also highly fuel efficient: for the same fuel mass, fusion would produce nearly 4 million times the energy produced by burning coal and four times the energy produced by nuclear fission. As for the fuels required for fusion, they are more readily available then those used in fission. Although several combinations of light elements are viable fuels, reacting deuterium (a hydrogen isotope with one proton and one neutron) and tritium (a hydrogen isotope with one proton and two neutrons) is the most effective. Deuterium can be easily extracted from seawater and, although tritium is very rare, it can be generated in the fusion reaction itself by using lithium. In the reaction between deuterium and tritium, a neutron is released:

If this neutron then reacts with Lithium-6 or Lithium-7, it splits the lithium into tritium and helium:

Lithium is therefore another part of the fuel needed for nuclear fusion and there are large stores of it on Earth. It must be admitted, however, that lithium is in high demand and mining it can harm the environment. Still, with massive fuel efficiency, no greenhouse gas emissions and no risk of nuclear meltdowns, achieving nuclear fusion would, on balance, be a game-changer for the environment.

Considering the above, fusion sounds like the perfect solution to our increasing demands for sustainable energy - so why haven’t we started using it yet? There is, it turns out, a slight issue – fusion requires temperatures around 100 million degrees Celsius to take place. This is due to the repulsive forces between the nuclei (since they are positively charged and like charges repel) which need to be overcome in order for the nuclei to come close enough to fuse. For fusion to take place the atoms need to have enough energy to collide and there need to be enough atoms in a given volume, which is why such high temperatures and pressures are required. Additionally, you need some way to confine the very dense hot hydrogen plasma (a gaseous mixture of ions and free electrons). There are currently two main methods being researched for achieving these conditions: magnetic confinement and inertial confinement.

The name “magnetic confinement” gives away the basics of how this method works. In the most common version (the tokamak), the plasma is confined in a doughnut-shaped chamber using magnetic and electric fields. Using a combination of microwaves, an induced electric current and accelerated particles the plasma is heated to the required temperature. Alternatively, the more recent idea of inertial confinement focuses lasers onto a tiny pellet of deuterium-tritium fuel, which is heated and compressed until fusion can take place. The national ignition facility in California is experimenting with this method using 192 laser beams!

Powering the world with nuclear fusion, however, is still quite far off from becoming a reality, since no one has successfully managed to use it to create a gain in energy (when more energy is generated than is used to power it). Fusion has even been jokingly dubbed the technology that is always 30 years away! There are, however, numerous promising companies attempting to tackle the problem and advances continue to be made. It’s a puzzle still to be solved!

What do you think of nuclear fusion? Let us know!

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