Nuclear Fusion - The Future of Nuclear Energy?

A month or so ago I talked about ‘the science behind a nuclear power plant’ with a brief description of nuclear fission, which is the process of splitting an atom into two smaller atoms and is the way we harness nuclear energy for electricity at the moment. Today I’ll be talking about nuclear fusion, which is seen by some scientists as the way forward for nuclear power and part of the key to a greener future with near unlimited energy supply.

Nuclear fusion, in the way most people will know about it, is the process that powers the sun and ultimately is responsible for all life as we know it on this planet (ITER 2016). In the sun, hydrogen atoms are fused together a number of times to produce a helium atom, and it is this fusing of atoms that produces the energy.

Nuclear Fusion Process in the Sun (Wikipedia 2016)

However on Earth, things have to be done slightly differently; the nuclear fusion that occurs in the Sun begins at roughly 15 million °C, which is pretty hot as you’d imagine (FusionForEnergy 2015). Sadly on Earth, we don’t have it as easy. Due to the sheer size of the sun, it emits immense gravitational forces which produce intense pressure as well as a high heat which allow it to carry out its nuclear fusion (WNA 2016). On earth, we are not able to produce pressures on such a magnitude so we have to compensate for this by increasing the temperature input to around 50 million °C (WNA 2016). The most efficient and feasible reaction scientists are able to perform at the moment is a fusion of deuterium and tritium, which is essentially two different heavy forms (isotopes) of hydrogen (HyperPhysics 2016).  The tritium and deuterium are fused together and a helium atom is created, with a neutron as a by-product; it is this reaction that produces the energy. The aim is to get enough of these fusion reactions to occur continuously that the process will be self-sufficient, and more energy will be produced than is inputted. When this is achieved, nuclear fusion will produce 4 times the energy yield of fission, and for every time pressure within the reaction is doubled, the energy produced is increased four-fold (WNA 2016) (MIT News 2016).

D-T Nuclear Fusion Process on Earth (AtomicArchive 2015)

Now this is all sounds amazing, but there must be some reasons why we aren’t doing this right now; and there are quite a few as you’d imagine. First up is that extremely high temperature that is required to even begin the reaction. This is needed to overcome the electrostatic forces that act as a gateway to the fusion of the hydrogen atoms (WNA 2016). The issue isn’t creating the temperatures, but creating a device that could contain such a reaction for long periods of time. Without a long enough time period, the fusion reaction wouldn’t be able to be self-sufficient and have a net-energy output (WNA 2016). Secondly there is a slight issue of fuel; while the deuterium occurs naturally in seawater (the deuterium in a gallon of seawater has the energy equivalent of 300 gallons of gasoline), the tritium is a bit harder to come by (HyperPhysics 2016). The tritium has no sizeable natural source and due to its radioactivity, has a half-life of around 12 years, which means it has to be bred from lithium; this could possibly be a bottleneck in fuel supply (HyperPhysics 2016). Finally a big problem is the cost and scale it is going to take to research and finally produce a workable reactor. Initial costs of a fusion power plant are estimated to be around £10 billion, but the research for it is even higher, with ITER (International Thermonuclear Experimental Reactor) the centre of nuclear fusion experiments expecting to cost over €20 billion to even construct let alone run the experiments (EUROfusion 2016) (Bloomberg 2016). As fusion reactions are in a gas form compared to fission which occurs in a solid form, the energy released is less concentrated, so fusion reactors will be bigger and more costly to build and maintain (WNA 2016).

ITER Construction Site (Science 2015)

Other than the near unlimited energy that seems oh so far away, are there any other positives? Well, like nuclear fission they would only have a negligible contribution to greenhouse gas emissions if any and are seen as a way to help reduce our CO₂ emissions (WNA 2016). Unlike fission, fusion reactors are easily shutdown and it would be near impossible for a Chernobyl or Fukushima situation to occur (CCFE 2016). The issue of containing the reaction is also seeing positive results, with magnetic fields which hold the plasma where the reaction takes place being the preferred method (MIT News 2016). In terms of waste, no long-lived radioactive products are produced and any unburnt gas is dealt with on sight. There is the slight issue about the reactor structure itself becoming radioactive due to long-term bombardment of high-energy neutrons, but the radioactivity itself would be easily dealt with (WNA 2016). A big concern is a tritium release into the surrounding environment, however this is hoped to be dealt with by forgoing tritium altogether, and just fusing deuterium with deuterium instead (WNA 2016).

Nuclear Fusion Reactor with Magnetic Field (FusionForEnergy 2015)

Nuclear fusion is often seen as the finish line for nuclear energy, and part of the end game in reaching our planet's energy needs. With nuclear fusion experiments breaking previous records and devices containing the reaction for longer periods of time and at higher pressures being built, it seems we are edging closer to the goal (MIT News 2016). However, a long-running joke since the 70’s is that commercial nuclear fusion is always 40 years away, and as you can probably guess, is the latest estimate for now as well (CCFE 2016). Perhaps nuclear fusion is just one nut we’ll never be able to crack?

If you have any questions or are just curious about nuclear fusion, don’t hesitate to leave a comment down below and I’ll get back to you as quick as I can.