What kind of reaction is 'nuclear fusion'? Why is it expected to be the clean energy of the next generation?
Unlike nuclear fission, 'nuclear fusion' has the characteristic of emitting almost no radioactive waste and emitting no greenhouse gases. Scientific media LiveScience explains what kind of reaction this nuclear fusion is.
What is nuclear fusion?
The reaction in which light nuclides fuse together to form heavier nuclides is called `` nuclear fusion (nuclear fusion reaction) ''. Nuclear fusion also occurs inside stars, etc., and the power generation method using this has the characteristics of `` generating almost no nuclear waste '' and `` not emitting greenhouse gases '', so it can be used as a conventional energy source. It is attracting attention as one of the clean energy sources.
During fusion, the total mass of the new heavier nuclei is less than the total mass of the two lighter nuclei. The mass lost at this time is released as energy, as explained in Albert Einstein 's equivalence of mass and energy .
Normally, nuclei repel each other because they have the same electric charge. In order to cause nuclear fusion, it is necessary to overcome this repulsive force, which seems to require high temperature, high pressure, or both. According to Oak Ridge National Laboratory, fusion reactors on Earth rely on high temperatures because they can't replicate the pressures of the core of a star , about six times the core temperature of the sun. seem to reach. This extremely high temperature transforms hydrogen from a gas to plasma, a very high-energy state of matter in which the electrons are stripped from the atoms in the fusion reactor.
If more energy than this 'energy necessary to cause nuclear fusion' can be obtained after the reaction, nuclear fusion is a clean energy unlike nuclear fission, so it will be a very useful energy source for human beings. Therefore, scientists have been working for decades to pursue this goal.
And on December 13, 2022, the United States Department of Energy finally announced that it had succeeded in producing more energy through nuclear fusion than was needed to cause it. In the experiment, researchers at Lawrence Livermore National Laboratory irradiate about 200 high-power lasers to confine the plasma of hydrogen isotopes deuterium and tritium, causing nuclear fusion.
However, experts say commercial fusion reactors are likely to be decades away. The reason is that the amount of energy required to trigger the reaction is too enormous. Heating the plasma requires drawing energy from the power grid, so considering the amount of energy lost when the power supplied to the fusion reactor is converted to light, it is possible to generate quite an enormous amount of energy. It has to be.
At the time of writing the article, the most promising thing on earth is to fuse deuterium and tritium (tritium). The process requires temperatures as high as 39 million degrees Celsius and can generate 17.6 million electron volts of energy. Deuterium and tritium fusion is underway at the DIII-D National Fusion Facility in San Diego, California. A similar fusion experiment is underway in France's ITER project, which uses a tokamak-type fusion reactor that uses powerful magnets.
Deuterium-deuterium fusion is more promising than deuterium-tritium fusion because it is theoretically easier to get two deuterium atoms and the energy yield produced is higher. . This method also requires very high temperatures. According to ITER, some test fusion reactors can reach temperatures of about 150 million degrees Celsius, but deuterium-to-deuterium fusion can reach temperatures of at least 400 million to 500 million degrees Celsius. You will need the temperature. Therefore, it cannot be said that the fusion of deuterium and deuterium is closer to realization than the fusion of deuterium and tritium.
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