The chemical element boron, the solution to one of the challenges of nuclear fusion

18/12/2024
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Cámara de vacío del reactor ITER. Fuente: ENSA
ITER reactor vacuum chamber. Source: ENSA

Nuclear fusion involves the fusion of deuterium and tritium nuclei, the two isotopes of hydrogen involved in the reaction. This process generates impurities and ashes that can affect the reaction, decrease its performance, and interact with the plasma containing the deuterium and tritium with the most exposed layer of the mantle lining the inside of the reactor vacuum chamber. The reactor chamber is one of the most essential elements and has the challenge of withstanding the impact of the high-energy neutrons resulting from the fusion of the nuclei. Therefore, the future lies in developing a technology that transports these impurities and ashes to the outside.

The best-known nuclear fusion project is the International Thermonuclear Experimental Reactor (ITER) being built in Cadarache (France). There are 54 identical pieces of stainless steel called ‘divertor’ that form the base of the reactor's vacuum chamber and have tungsten shields that are responsible for withstanding the bombardment of the high-energy neutrons from the plasma, transforming their kinetic energy into heat that is cooled by the water circulating inside the ‘divertor’. These parts are also responsible for purifying the plasma so that impurities and ash do not degrade the fusion reaction.

However, rather than removing impurities and ashes from the plasma, research is being done to prevent them from being produced and entering the vacuum chamber. Boron has been considered for this purpose. A chemical element of the periodic table of the elements with the symbol B and atomic number 5. It is a metalloid and semiconductor element abundantly present in the mineral borax or colemanite and dissolved in seawater. Its physicochemical properties allow it to be used to spread a thin layer on the surface of the elements in the vacuum chamber that are directly exposed to the plasma to significantly reduce impurities and increase the reaction yield.

The boron deposition process inside the reactor is known as ‘boronisation’ and is being tested with very good results in reactors in Germany, France, and Switzerland.