For fusion to be possible, the nuclei must be brought close together, using a great deal of energy to overcome the electromagnetic repulsion. The fusion of the elements up to atomic numbers 26 and 28 iron and nickel is an exothermic reaction, it emits energy since the nucleus produced by the reaction has a mass lower than the sum of the masses of the reacting nuclei.
For atoms with higher atomic numbers, the reaction is endothermic, it absorbs energy. Some reactions, primarily those with a lower energy threshold, such as the fusion of deuterium and tritium, result in the release of one or more free neutrons; this creates, in the perspective of exploitation as an energy source, some important technological problems related to neutron activation and shielding.
The process of fusion of atomic nuclei is the mechanism at the basis of stars, making it possible for them to emit light and maintain a constant size by preventing their gravitational collapse. Fusion was artificially produced for the first time in the 1950s to amplify the power of an atomic bomb.
How nuclear fusion occurs
This type of device was called the H-bomb. Since the 1960s, many experiments have been carried out to exploit the energy produced by fusion, primarily to produce electricity. Fusion reactors are still being designed and built.
The work is believed to be finished around 2060. Controlled nuclear fusion could solve most of the energy problems on earth, because it could produce almost unlimited quantities of energy without emissions of harmful gases or greenhouse gases and with the production of limited quantities of radioactive waste including tritium; a small amount of residual radioactivity would affect only some components of the fusion reactor subjected to neutron bombardment during the fusion processes.
Moreover, these components would be easily replaceable; the half-life of the residual radioactivity would be comparable with the average life of the plant. On December 5, 2022, a group of researchers from the National Ignition Facility at the Lawrence Livermore National Laboratory carried out for the first time an inertial confinement fusion with a positive energy balance.
The 2.05 MJ supplied to the target in fact generated 3.15 MJ of power. However, 300 MJ of energy were needed to power the 192 lasers. The overall energy balance was therefore extremely negative. The research results were officially announced on December 13, 2022 in Washington.