Nuclear fusion: what it is and why it is difficult to produce it
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The nuclear reactions that produce energy are of two types: the fissionin which a heavy atomic nucleus separates into two lighter nuclei, and la fusionwhich releases energy when two light nuclei combine into a heavier nucleus.
There nuclear fusion it is a phenomenon that assumes great importance in nature, because it is the basis of the functioning of stars such as the Sun. On Earth, fusion has so far been exploited to make the so-called thermonuclear or hydrogen bombs, while since the post-war period the possibility of carrying out reactions of “controlled” nuclear fusion to produce electric energy on an industrial scale, as is already the case with fission reactors.
How nuclear fusion occurs
In order for the fusion to take place, it is necessary to bring i two cores at an extremely close distance (of the order of a millionth of a billionth of a metre), in order to overcome their electrostatic repulsion: to do this, the nuclei must be confined to a very high density and temperature – we are talking about millions of degrees Celsius -, for example by means of magnetic fields: a very complicated operation from a technical point of view and costly in terms of energy. Most of the efforts of scientists are in fact concentrated in the construction and commissioning of plants capable of isolating these very high temperatures.
In order for the fusion reaction to produce useful energy, the energy produced by the reaction must be greater than that expended by the plant to operate.
Fusion energy is “clean”, i.e. it does not generate radioactive waste or residues (as occurs instead in fission reactors). THE fusion reactors do not polluteusing as fuel thehydrogenpractically inexhaustible. For this the nuclear fusion today it is considered one of the possible energy alternatives to fossil sources and to the intermittence of renewables.
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Nuclear fusion reactors
From the 1950s to today, various reactor technologies have been developed and, among the various ones, the most used are those magnetically confined (tokamak, stellator and inverted field necking systems) and a inertial confinement.
One of the most famous tokamak reactors is the Joint European Tour (JET), built in the 1970s near Oxford, UK. In the 90s in Italy was inaugurated the Frascati Tokamak Upgrade (FTU), from whose ashes the Divertor Tokamak Test (DTT). It was a reactor created to study and improve the divertor, a component now essential for removing the heat generated and fusion products from reactors.
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The ITER project
One of the most ambitious experimental projects is the ITER reactor (International Thermonuclear Experimental Reactor) made at Cadaraches, in France, the result of an international collaboration between Europe (France and Italy at the forefront), Japan, China, Russia, Korea. Its construction should end in 2025 with the aim of becoming the first plant capable of producing as much energy as will be spent to operate it.
If this reactor – designed to produce an amount of energy 10 times higher than that used to trigger nucleate fusion – is successful, the construction of DEMO (DEMOnstration Power Plant), an ITER-like reactor designed to produce power for distribution into the power grid.
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