The big advantage of nuclear fusion is that large amounts of energy can be produced using just a few grams of fuel. More specifically, one gram of fuel in the fusion process has the potential to produce the equivalent of eight tons of oil. Likewise, the sun is able to supply the entire planet Earth with energy through fusion reactions.
It is the same as nuclear fission, the process used to produce energy in nuclear power plants today: the amount of fuel required (in this case uranium) is very small compared to the amount of fuel required by thermal power plants. Coal, gas or oil. No matter how massive the use of fusion energy may be in the future, its use (due to the extraction of necessary materials or the emission of gases) will never be so large as to change the composition of our atmosphere. In addition, fusion is an energy that does not emit greenhouse gases.
In order to realize fusion reactors, the use of hydrogen isotopes will be necessary. Isotopes are atoms of the same element (with the same number of electrons and protons) but with different numbers of neutrons. This property means that the different isotopes of an element have the same chemical properties but different physical properties. The fusion reactions that occur at the lowest temperature are those between deuterium and tritium. Deuterium is very common in seawater and is obtained there through hydrolysis. And the tritium is produced in the fusion reactor itself, as the neutrons from the fusion reactions hit a regenerating jacket that consists, among other things, of lithium. A neutron and a lithium produce the product tritium, which is reused as fuel in the plasma. Plasma is the material that allows nuclei to fuse and produce energy. It is an ionized gas with a temperature of more than a hundred million degrees.
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In fusion, as it also occurs in fission, we speak of nuclear reactions, in contrast to the processes of fuel combustion we know, which are processes based on chemical reactions. During fusion, we need to bring the nuclei closer together so that the nuclear forces come into play and strongly attract each other. When they fuse, they form a new element whose mass weighs less than the sum of the masses of the original nuclei. This mass difference (although almost insignificant) can be converted into energy through Einstein’s famous equation E=mc². And you should know that we started with very light elements. As I explained to you, we use the isotopes of hydrogen, nature’s lightest element, which ranks first in the periodic table because it only has one proton and one electron. And next comes helium. By combining two hydrogens through the nuclear fusion reaction we get helium and an excess which is a neutron and has a lot of energy.
To give you an idea of how much material we need as fuel, in the plasma confinement machines we use for fusion experiments we have a density a million times less than the density of the air we breathe. This means that there are very few particles. The density is so low that the composition of the atmosphere can never be changed, no matter how many reactions occur when helium is released. Neither through the consumption of hydrogen nor through the emissions caused by fusion reactions, because these emissions also do not contain any CO₂.
Isabel García Cortes She is a senior scientist at the Fusion Laboratory of the Center for Energy, Environment and Technology Research (CIEMAT).
Question emailed from Leonardo Arrabé
Coordination and writing:Victoria Toro
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