With energy demand constantly increasing and the supply of fossil fuels going down, finding an alternative source of energy is required. Fusion is the process which powers the stars but could soon be used to generate electricity on Earth.
Fusion is a process which takes place inside stars, it is a reaction involving hydrogen and its isotopes deuterium and tritium.
The overall reaction is:
Four hydrogen nuclei (protons) are converted into one helium nuclei. Two electrons, two positrons, two neutrinos and 2 gamma photons are also produced – along with huge amounts of energy.
This reaction is slightly more complex than the above equation shows. Firstly two protons form a deuterium nucleus, releasing an electron and neutrino. Then one proton reacts with the deuterium to produce a tritium nucleus and gamma photon. Two tritium nuclei then collide and produce two protons and a helium nucleus. This is one example of the fusion process, but the above steps can vary. Overall, however, it produces the above equation.
This process only happens at extremely high pressure and temperature – over a million degrees. The atoms then form a plasma and have enough energy to fuse. Although there are high demands for energy input, a greater amount of energy is released. The reason for the energy release is the idea of binding energy and the famous equation E = mc2
Calculating Energy Released
For the nucleus of an atom to stay together a certain amount of energy is required, called binding energy. This varies for different atoms. The nucleus actually has a lower mass than the individual nucleons within it, this difference is called the mass defect. This value can then be used to calculate binding energy using E = mc2.
In fusion the total binding energy of the produced nuclei is bigger than the individual binding energies of the smaller nuclei. The overall mass is reduced and energy is then released. This ensures mass-energy is conserved.
The energy released in fusion can be calculated by the process below:
- Find the difference between the mass of reactants and mass of the products
- Substituting this value in for m, use E = mc2 to calculate energy released
- Using moles, the energy released per gram can be calculated.
The ITER fusion reactor in France aims to produce 500MW from just half a gram of hydrogen. However, the power input required, although lower is still huge, around 50MW.
A Possible Energy Resource?
Currently there are no fusion power stations however there is a lot of research currently taking place to improve the power output of the process. There are some problems which must still be overcome, with the biggest challenge being maintaining a high temperature to allow the fusion to occur.
Fusion has a lot of advantages over current processes to generate power.
- Unlike fission it doesn’t make radioactive products.
- The resources required are abundant, hydrogen and deuterium are found in sea water.
- High energy released, over a million times more energy output than coal or gas. Four times higher energy output than fission reactions.
- No harmful greenhouse gases produced, main product is helium.
- No risk of meltdown, unlike fission, it would stop immediately if there was an issue as the temperature would drop too low and the reaction would stop.