Nuclear fusion was discovered about a hundred years ago as the sun's energy source. Nuclear fusion involves the fusion of two atomic nuclei, whereas nuclear fission (nuclear power plant) involves the splitting of atomic nuclei. The fusion of two atomic nuclei can release energy, with each reaction releasing millions of times more energy than the combustion of fossil fuels. To initiate the nuclear fusion process in a fusion reactor, the so-called fusion plasma, a suitable mixture of substances, must be heated to very high temperatures, e.g. to more than 100 million degrees Celsius for deuterium-tritium. It has not yet been possible to generate usable energy from the nuclear fusion process.

The majority of scientists worldwide are conducting research into deuterium-tritium fusion (D-T fusion), which is based on magnetic confinement fusion. In other words, nuclear fusion is to be achieved technically by means of a magnetic field. In D-T fusion, the chemical elements deuterium (non-radioactive) and radioactive tritium are used as fuels. Deuterium and tritium are isotopes of the element hydrogen. Alternative concepts such as laser fusion are increasingly being pursued for energy generation. In this process, fusion is not realised by means of a magnetic field, but by means of high-energy lasers.

The fusion of a D and T nucleus produces a helium nucleus and a neutron. The neutron carries the released energy as kinetic energy (neutron radiation). The energy of the helium nucleus is used to maintain the plasma temperature, but thermal energy is required as well. Furthermore, the plasma must be enclosed by a magnetic field in the case of magnetic confinement fusion. The fusion reaction will then take place in the plasma of the heated D-T mixture, which is located in a vacuum chamber. To generate electricity, the energy of the neutron or neutron radiation is converted into heat in special components known as blankets. The heat is then used to drive a turbine to generate electricity by means of a cooling medium and heat exchangers - similar to a conventional nuclear power plant or conventional fossil-fuelled power plants.

It is estimated that a potential power plant with an electrical output of 1000 megawatts would require a small three-digit kilogramme amount of deuterium and tritium fuel per year for D-T fusion; but, at present, this is just an assumption (Source: ‘DEMO’ project, Gianfranco Federici from EUROfusion; FEC 2023; 16-21 October 2023, London, UK). By comparison, nuclear power plants require around 170 tonnes of uranium per year (= around 80,000 tonnes of rock). Deuterium as a raw material is extracted from water. The radioactive and highly volatile hydrogen isotope tritium, which has a half-life of 12.3 years, requires breeding in the blanket (= nuclear reaction). Numerous unresolved technical questions remain as to how the breeding of tritium is to be achieved.