Comprendre la fusion nucléaire, l’énergie des étoiles, en 7 questions

La fusion nucléaire doit servir à produire une énergie propre et beaucoup plus conséquente que celle issue la fission nucléaire.

An old sea serpent of energy politics, nuclear fusion is coming back to the fore, thanks to the comeback in favor of the nuclear industry. The recent bill aimed at reducing inflation and mitigating climate change promulgated in the United States (“Inflation Reduction Act”) thus allocates 280 million dollars to the national program for the development of nuclear fusion. The point in seven questions about this technology, which has fueled the hopes and fantasies of scientists for almost a century.

1. What is nuclear fusion?

Nuclear fusion is a nuclear reaction in which two atomic nuclei fuse together to create a new, heavier nucleus. This reaction is present in the sun and almost every star in our Universe, leading many observers to refer to nuclear fusion as “stellar energy.”

During this operation, a very large amount of energy is created, which could theoretically be used to produce electricity in new generation nuclear power plants.

2. What is the difference with nuclear fission?

While nuclear fusion consists of the fusion of two light atoms -such as hydrogen for example-, nuclear fission is the opposite reaction: a heavy nucleus splits in two under the impact of a neutron, a small particle present in the nucleus of all atoms. . In today’s nuclear power plants, uranium is the element made up of heavy nuclei that will split apart under the impulse of a neutron.

La fission s’accompagne aussi d’un grand dégagement d’energie et en même temps, de la libération d’autres neutrons, lesquels vont à leur tour casser d’autres noyaux, dégager de l’énergie et libérer d’autres neutrons, and so right away. This is called a chain reaction.

3. What are the advantages of nuclear fusion?

The main advantage of nuclear fusion is that it releases a much higher amount of energy than fission without producing radioactive waste for thousands of years. In addition, being based on hydrogen nuclei (deuterium and tritium), the process would provide clean and practically inexhaustible energy. Deuterium is found in water, and tritium is easily produced from lithium, a metal found in abundance in the earth’s and oceanic crust.

Proponents of nuclear fusion also point to another advantage, of a safety nature, namely the absence of the possibility of a nuclear accident. In the event of a problem, the plasma contained in a nuclear fusion reactor cools down in a few seconds and the reactions are interrupted. Therefore, there would be no risk of leakage endangering the nuclear power plant.

4. Which countries are active in the field?

The first research on nuclear fusion began in the 1920s in England. This fever will gradually conquer many developed countries after World War II, including the United States, the USSR, England, France, Germany, and Japan.

But it was not until the 1980s that the contours of an international collaboration were drawn. At the 1985 Geneva summit, the two superpowers, the US and the Soviet Union, agreed to work hand in hand to develop nuclear fusion.

This approach finds a concrete application in the Iter project. Located in Saint-Paul-Lez-Durance, in Bouches-du-Rhône, this €20 billion international initiative brings together 35 countries, including the countries of the European Union, Russia, the United States and China.

The tokamak at the heart of the Iter nuclear power plant, in Caradache (Bouches-du-Rhône).Daniel Cole/AP/SIPA

Its objective is to reach an industrial application of this technology, with the construction of a civil nuclear reactor with nuclear fusion. Currently in the assembly phase, the reactor should carry out its first test in 2025.

5. Is nuclear fusion really clean energy?

In theory, nuclear fusion should be used to produce energy that is clean and four times more consistent than energy from nuclear fission with the same fuel. The process also releases no CO2 and only generates helium, a non-toxic gas that is not part of the greenhouse gas family.

However, if nuclear fusion power plants do not produce any long-lived, high-level radioactive waste, they still generate radioactive waste.

Jérôme Bucalossi, director of the Institute for Research on Fusion by Magnetic Confinement (IRFM) of the Atomic Energy Commission (CEA), however, explained to “Echos” that the radioactivity of this waste “could be deactivated in about ten years, a century maximum’, versus thousands of years for the most radioactive in the case of a nuclear fission reaction.

However, there remains the thorny question of the materials at the origin of the plant -such as beryllium- whose extraction would be polluting.

6. When will nuclear fusion be used specifically?

This is the question that haunts all industry watchers. For decades, the advancement of nuclear fusion was limited to isolated experiments, which set new records for plasma temperature or holding times.

In recent years, many projects have been launched with the aim of having an operational nuclear fusion reactor by 2030. This is the case of the Iter project, which expects tests to begin in 2025. However, many experts agree that the Industrial use of this technology is unlikely to occur before mid-century.

Enough for Greenpeace to say that “nuclear fusion remains a glossy paper mirage” costing “billions of euros of public money with no guarantee of results.”

7. Is the private sector investing in this technology?

Long reserved for states, nuclear fusion is gaining traction with private companies, including Marvel Fusion. The Bavarian start-up, which has raised nearly €65 million since its inception, plans to launch a prototype power plant in 2027 before commercializing its solution in the 2030s.

However, it is in the United States where the frenzy is most intense. Various investors are interested in nuclear fusion, not least: Jeff Bezos, Bill Gates or even George Soros have invested in young shoots in the sector.

The Amazon chief is backing Canadian startup General Fusion, which has also benefited from state investment, in its $400 million nuclear power plant project in Culham, England. For their part, Bill Gates and George Soros participated in the fundraising of Commonwealth Fusion Systems, which allowed the American company to raise 1,800 million dollars.

A total of 25 private companies entered the merger business in 2021. About $3.5 billion were raised in the markets, according to data from the PitchBook agency.

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