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Find out what tritium is, the nuclear fuel used by fusion reactors and why only 20 kg are produced per year in the world

11 June 2024 to 10: 02
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energy - nuclear energy - nuclear fusion - tritium
We explore nuclear fusion as the nuclear energy of the future. Learn how tritium is produced and used in experimental reactors like ITER

We explore nuclear fusion as the nuclear energy of the future. Learn how tritium is produced and used in experimental reactors like ITER

Tritium, essential for nuclear energy, present in nature is extremely rare. This radioactive isotope of hydrogen is produced naturally in the upper layers of the atmosphere through the interaction of cosmic rays with the nuclei of atmospheric gases, but its production is very modest. In fact, only a few kilograms are produced annually in Earth's atmosphere. So few, in fact, that scientists estimate we can count them on our fingers

Interestingly, not all tritium available on our planet has a natural origin. Atmospheric nuclear tests carried out between the end of the Second World War and the 80s released a few tens of kilograms of this isotope into the oceans. Additionally, CANDU-type nuclear reactors, which are pressurized heavy water devices developed in Canada, also produce it. Each 600 MW reactor generates around 100 g of tritium annually, resulting in an annual global production of around 20 kg.

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ITER, the experimental nuclear fusion reactor that an international consortium led by the European Union is building in Cadarache, France, will use as fuel two isotopes of hydrogen: deuterium and tritium. As we have just seen, tritium is very scarce, but what is currently accumulated across the planet is sufficient to ensure that this experimental fusion energy reactor has what it needs throughout its operational life, which will extend for approximately fifteen years.

ITER will test an innovative strategy to produce large quantities of tritium.

The problem is that after ITER will come DEMO, which will be the nuclear fusion demonstration reactor that aims to prove the viability of this technology to produce large amounts of electricity. And after the DEMO, if everything goes as planned by ITER engineers, the first commercial nuclear fusion power plants will appear. Each of its reactors will need between 100 and 200 kg of tritium annually, so it is clear that the math does not add up.

CANDU reactors cannot generate the large quantities of tritium that fusion machines will need, but, fortunately, this dilemma has a solution. A very ingenious one.

These are the deadlines that ITER currently manages to demonstrate the feasibility of nuclear fusion. The purpose of scientists working on nuclear fusion through magnetic confinement, the strategy currently used by the experimental reactors JET, in Oxford (England), and JT-60SA, in Naka (Japan), is that future fusion energy reactors are capable of to generate all the tritium they need on their own. That they are capable of self-supply. This plan proposes that the external contribution of tritium be minimal and restricted to very specific moments in the operational life of the nuclear fusion reactor. It looks promising, but the most interesting thing is how they are going to do it.

Challenges and Technological Solutions for Tritium Self-supply

And, on paper, what they're going to do is simple: they're going to put lithium in the coating that covers the inside of the fusion reactor's vacuum chamber. One of the byproducts resulting from the fusion of a deuterium nucleus and another of tritium is a neutron that is ejected with an energy of around 14 MeV. When one of these particles hits one of the lithium atoms housed in the chamber's coating, it changes its structure, thus producing a helium atom, which is a harmless chemical element, and a tritium atom. Here it is. This is exactly what fusion power reactors need. On paper it seems like a simple idea, but putting it into practice is not easy.

The challenges that implementing the technological solutions required for self-supply of tritium present are enormous. On the one hand, it is essential that the ratio between the high-energy neutrons produced in fusion and the tritium atoms generated on the walls of the vacuum chamber is ideal. Furthermore, it is necessary to resolve the transport of tritium from the place where it is generated to the place where it will be consumed, and this is not trivial because it is a gas that disperses easily, especially at high temperatures. This procedure presents other challenges, but these two are critical. Let's cross our fingers that tritium regeneration in ITER goes well.

Cover image: ITER

Source: Fusion for Energy , ITER

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