Nuclear fusion is a reaction where two atomic nuclei come together to form a heavier nucleus.
This process releases energy because the weight of the heavy nucleus is less than the sum of the weights of the lighter nuclei. This mass defect is transformed into energy (through the formula E = mc2). Although said mass defect is very small and thus the gain is also very small, it must be considered that it is a highly concentrated energy. There are millions of atoms in one gram of matter, which means that a small amount of fuel will release a large amount of energy.
This process releases energy because the weight of the heavy nucleus is less than the sum of the weights of the lighter nuclei
Not all fusion reactions produce the same energy. It always depends on the nuclei being fused and on the reaction products. The most easily achievable reaction is that of deuterium (one proton and one neutron) and tritium (two neutrons and two protons) to form helium (two neutrons and two protons) and a neutron, which releases an energy value of 17.6 MeV.
It is a practically endless source of energy, since deuterium can be found in sea water and tritium is easily produced from the neutron that escapes the reaction.
What technology is used in fusion?
The reaction described above is the easiest to achieve, but this does not mean that it is easy to produce energy from fusion reactions. In order to do that, the nuclei of two atoms must come together. The problem is that these nuclei are positively charged, which means that the closer they move to each other the more they will repel each other. A possible solution would be to accelerate them in a particle accelerator and make them crash together, but the energy needed for the acceleration process would be greater than that which would be produced by the reaction.
Fusion by inertial confinement. In order to resolve this problem, fuel spheres are compressed with laser or particle beams. This produces what is known as fusion by inertial confinement, producing very elevated densities and bringing the nuclei very close together. A tunnel effect causes them to fuse, releasing energy.
Fusion by magnetic confinement. Another method to produce fusion reactions in such a way that energy is gained is to heat up the fuel to temperatures of millions of grades, making nuclei crash due to thermal agitation, also through the tunnel effect. At such elevated temperatures, the fuel breaks down into positively and negatively charged particles, and can be controlled through magnetic fields. This is magnetic confinement fusion.
Not all fusion reactions produce the same energy. It always depends on the nuclei being fused and on the reaction products
Advantages of fusion
Nuclear fusion is a potential large scale energy resource, with many advantages as respects other types of resources:
- Primary fuels are cheap, plentiful, non radioactive, and geographically and evenly widespread (lake and ocean water contains enough heavy hydrogen for millions of years at the current rate of energy use).
- An intrinsically safe system: the reactor only contains the fuel for the next ten seconds of operation. The fusion reaction is not a chain reaction; it is not possible to lose control. The reaction can be halted at any time by simply closing down the fuel supply.
- Fusion does not produce gasses that contribute to the greenhouse effect. The reaction itself only produces helium, a non harmful gas.
- The radioactivity of the reactor structure, produced by the neutrons released in the fusion reactions, can be minimized by carefully choosing low activation materials. For this reason it is not necessary to store the reactor elements for longer than 50 years.
The ITER project
In order to prove the feasibility of nuclear fusion, in 1986 an international consortium known as ITER (International Thermonuclear Experimental Reactor) was created, located in Cadarache (France).
Its goal is to test all the necessary elements for the construction and functioning of a nuclear fusion reactor that would serve as commercial demonstration, in addition to bringing together the technological and scientific resources from the investigation programs in development up to then.