The tritium that is present in nature is very scarce. very little This radioactive isotope of hydrogen occurs naturally in the upper layers of the atmosphere due to the interaction of cosmic rays and the nuclei of atmospheric gases, but its production is very modest. In fact, only a few kilograms are produced annually in the Earth’s atmosphere. So few, in fact, that scientists estimate we can count them on our fingers.
Curiously, not all the tritium that is available on our planet has a natural origin. Atmospheric nuclear tests that took place between the end of World War II and the 1980s have dumped a few tens of kilograms of this isotope into the oceans, and, in addition, CANDU-type nuclear reactors, which are heavy water devices under pressure developed in Canada, they also produce it. Each 600 MW reactor annually generates about 100 g of tritium, so its annual global production is about 20 kg.
ITER, the experimental nuclear fusion reactor that an international consortium led by the European Union is building in the French town of Cadarache, will use two isotopes of hydrogen as fuel: deuterium and tritium. As we have just seen, tritium is very scarcebut the current accumulated across the planet is enough to guarantee that this experimental fusion power reactor will have what it needs throughout its operational life, which will last approximately fifteen years.
The problem is that DEMO will come after ITER, which will be the demonstration nuclear fusion reactor that aspires to put on the table the validity of this technology to produce large amounts of electricity. And after DEMO, if all goes as planned by ITER engineers, the first commercial fusion power plants will arrive. Each of its reactors will need between 100 and 200 kg of tritium annually, so it is clear that the accounts do not work out. CANDU reactors cannot generate the large amount of tritium that fusion machines will need, but fortunately this dilemma is solvable. A very clever one.
ITER will test an innovative strategy to produce large amounts of tritium
The aim of the scientists working on nuclear fusion by magnetic confinement, which is the strategy currently used by the JET experimental reactors in Oxford, England, and JT-60SA in Naka, Japan, is that future nuclear fusion reactors fusion energy are capable of generating all the tritium they need on their own. That are capable of self-sufficiency. This plan proposes that the external contribution of tritium be minimal and limited to very specific moments in the operational life of the nuclear fusion reactor. It sounds good, but the most interesting thing is to know how they are going to do it.
One of the resulting by-products of fusion is a neutron that is ejected with an energy of about 14 MeV.
And, on paper, what they are going to do is simple: they are going to put lithium in the mantle that lines the inside of the vacuum chamber of the fusion reactor. One of the by-products resulting from the fusion of a deuterium nucleus and a tritium nucleus is a neutron that is ejected with an energy of about 14 MeV. When one of these particles hits one of the lithium atoms housed in the chamber’s mantle, its structure is altered, thus producing a helium atom, which is a harmless chemical element, and a tritium atom. Here we have it. This is just what fusion power reactors need. On paper it seems like a simple idea, but putting it into practice is not easy.
The challenges posed by the development of the technological solutions that are necessary to implement tritium self-supply are enormous. On the one hand, it is essential that the rate that relates the high-energy neutrons produced in the fusion and the tritium atoms generated in the walls of the vacuum chamber is ideal. In addition, it is necessary to solve the transport of tritium from the place where it is generated to the place where it will be consumed, and it is not something trivial at all because it is a gas that disperses easily, especially at high temperatures. This procedure poses other challenges, but these two are critical. Let’s cross our fingers that the tritium regeneration in ITER goes well.
Cover image: ITER
More information: Fusion for Energy | ITER
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