Does thermonuclear energy have a future?

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

For more than half a century, scientists have been trying to build a machine on Earth, in which, like in the bowels of stars, a thermonuclear reaction takes place. The technology of controlled thermonuclear fusion promises to mankind an almost inexhaustible source of clean energy. Soviet scientists were at the origin of this technology - and now Russia is helping to build the largest fusion reactor in the world.

The parts of the nucleus of an atom are held together by a colossal force. There are two ways to release it. The first method is to use the fission energy of large heavy nuclei from the farthest end of the periodic table: uranium, plutonium. At all nuclear power plants on Earth, the source of energy is precisely the decay of heavy nuclei.

But there is also a second way to release the energy of the atom: not to divide, but, on the contrary, to combine the nuclei. When merging, some of them release even more energy than fissile uranium nuclei. The lighter the nuclei, the more energy will be released during fusion (as they say, fusion), so the most effective way to get the energy of nuclear fusion is to force the nuclei of the lightest element - hydrogen - and its isotopes to merge.

Hand star: solid pros

Nuclear fusion was discovered in the 1930s by studying the processes taking place in the interiors of stars. It turned out that nuclear fusion reactions take place inside each sun, and light and heat are its products. As soon as this became clear, scientists thought about how to repeat what is happening in the bowels of the Sun on Earth. Compared to all known energy sources, the "hand sun" has a number of indisputable advantages.

First, ordinary hydrogen serves as its fuel, the reserves of which on Earth will last for many thousands of years. Even taking into account the fact that the reaction requires not the most common isotope, deuterium, a glass of water is enough to supply a small town with electricity for a week. Secondly, unlike the combustion of hydrocarbons, the nuclear fusion reaction does not produce toxic products - only the neutral gas helium.

Pros of fusion energy

Almost unlimited fuel supplies. In a fusion reactor, hydrogen isotopes - deuterium and tritium - work as fuel; you can also use the isotope helium-3. There is a lot of deuterium in seawater - it can be obtained by conventional electrolysis, and its reserves in the World Ocean will last for about 300 million years at the current demand of mankind for energy.

There is much less tritium in nature, it is produced artificially in nuclear reactors - but very little is needed for a thermonuclear reaction. There is almost no helium-3 on Earth, but there is a lot in the lunar soil. If someday we have thermonuclear power, it will probably be possible to fly to the moon for fuel for it.

No explosions. It takes a lot of energy to create and maintain a thermonuclear reaction. As soon as the energy supply stops, the reaction stops, and the plasma heated to hundreds of millions of degrees ceases to exist. Therefore, a fusion reactor is more difficult to turn on than turn off.

Low radioactivity. A thermonuclear reaction produces a flux of neutrons that are emitted from the magnetic trap and deposited on the walls of the vacuum chamber, making it radioactive. By creating a special “blanket” (blanket) around the plasma perimeter, decelerating neutrons, it is possible to completely protect the space around the reactor. The blanket itself inevitably becomes radioactive over time, but not for long. Letting it rest for 20-30 years, you can again get material with a natural background radiation.

No fuel leaks. There is always a risk of fuel leakage, but a fusion reactor requires so little fuel that even a complete leak does not threaten the environment. Launching ITER, for example, would require only about 3 kg of tritium and a little more deuterium. Even in the worst-case scenario, this amount of radioactive isotopes will quickly dissipate in water and air and cause no harm to anyone.

No weapons. A thermonuclear reactor does not produce substances that can be used to make atomic weapons. Therefore, there is no danger that the spread of thermonuclear energy will lead to a nuclear race.

How to light the "artificial sun", in general terms, it became clear already in the fifties of the last century. On both sides of the ocean, calculations were performed that set the main parameters of a controlled nuclear fusion reaction. It should take place at an enormous temperature of hundreds of millions of degrees: under such conditions, electrons are torn off from their nuclei. Therefore, this reaction is also called thermonuclear fusion. Bare nuclei, colliding with each other at breakneck speeds, overcome the Coulomb repulsion and merge.

Problems and solutions

The enthusiasm of the first decades crashed into the incredible complexity of the task. Launching thermonuclear fusion turned out to be relatively easy - if done in the form of an explosion. Pacific atolls and Soviet test sites in Semipalatinsk and Novaya Zemlya experienced the full power of a thermonuclear reaction already in the first post-war decade.

But using this power, except for destruction, is much more difficult than detonating a thermonuclear charge. To use thermonuclear energy to generate electricity, the reaction must be carried out in a controlled manner so that energy is released in small portions.

How to do it? The environment in which a thermonuclear reaction takes place is called a plasma. It is similar to gas, only unlike normal gas it consists of charged particles. And the behavior of charged particles can be controlled using electric and magnetic fields.

Therefore, in its most general form, a thermonuclear reactor is a plasma clot trapped in conductors and magnets. They prevent the plasma from escaping, and while they do this, atomic nuclei merge inside the plasma, as a result of which energy is released. This energy must be removed from the reactor, used to heat the coolant - and electricity must be obtained.

Traps and leaks

Plasma turned out to be the most capricious substance that people on Earth had to face. Each time scientists found a way to block one type of plasma leak, a new one was discovered. The entire second half of the 20th century was spent on learning to keep the plasma inside the reactor for any significant time. This problem began to yield only in our days, when powerful computers appeared that made it possible to create mathematical models of plasma behavior.

There is still no consensus as to which method is best for plasma confinement. The most famous model, the tokamak, is a donut-shaped vacuum chamber (as mathematicians say, a torus) with plasma traps inside and outside. This configuration will have the largest and most expensive thermonuclear installation in the world - the ITER reactor currently under construction in the south of France.

In addition to the tokamak, there are many possible configurations of thermonuclear reactors: spherical, as in the St. Petersburg Globus-M, bizarrely curved stellarators (like the Wendelstein 7-X at the Max Planck Institute of Nuclear Physics in Germany), laser inertial traps, such as the American NIF. They receive much less media attention than ITER, but they also have high expectations.

There are scientists who consider the design of the stellarator to be fundamentally more successful than the tokamak: it is cheaper to build, and the plasma confinement time promises to give much more. The gain in energy is provided by the geometry of the plasma trap itself, which allows one to get rid of the parasitic effects and leaks inherent in the "donut". The laser pumped version also has its advantages.

The hydrogen fuel in them is heated to the required temperature by laser pulses, and the fusion reaction starts almost instantly. Plasma in such installations is held by inertia and does not have time to scatter - everything happens so quickly.

The whole world

All thermonuclear reactors existing in the world today are experimental machines. None of them are used to generate electricity. None has yet succeeded in fulfilling the main criterion for a thermonuclear reaction (Lawson's criterion): to get more energy than was spent on creating the reaction. Therefore, the world community has focused on the gigantic ITER project. If the Lawson criterion is met at ITER, it will be possible to refine the technology and try to transfer it to commercial rails.

No country in the world could build ITER alone. It needs 100 thousand km of superconducting wires alone, and also dozens of superconducting magnets and a giant central solenoid for holding plasma, a system for creating a high vacuum in a ring, helium coolers for magnets, controllers, electronics … Therefore, the project is building 35 countries and more at once thousands of scientific institutes and factories.

Russia is one of the main countries participating in the project; in Russia 25 technological systems of the future reactor are being designed and built. These are superconductors, systems for measuring plasma parameters, automatic controllers and components of the divertor, the hottest part of the inner wall of the tokamak.

After the launch of ITER, Russian scientists will have access to all of its experimental data. However, the echo of ITER will be felt not only in science: now in some regions there have appeared production facilities, which in Russia did not exist before. For example, before the start of the project, there was no industrial production of superconducting materials in our country, and only 15 tons per year were produced all over the world. Now, only at the Chepetsk Mechanical Plant of the state corporation "Rosatom" it is possible to produce 60 tons per year.

The future of energy and beyond

The first plasma at ITER is planned to be received in 2025. The whole world is waiting for this event. But one, even the most powerful, machine is not all. All over the world and in Russia, they continue to build new thermonuclear reactors, which will help to finally understand the behavior of plasma and find the best way to use it.

Already at the end of 2020, the Kurchatov Institute is going to launch a new tokamak T-15MD, which will become part of a hybrid installation with nuclear and thermonuclear elements. The neutrons, which are formed in the thermonuclear reaction zone, in the hybrid installation will be used to initiate the fission of heavy nuclei - uranium and thorium. In the future, such hybrid machines can be used to produce fuel for conventional nuclear reactors - both thermal and fast neutrons.

Thorium salvation

Especially tempting is the prospect of using a thermonuclear "nucleus" as a source of neutrons to initiate decay in thorium nuclei. There is more thorium on the planet than uranium, and its use as a nuclear fuel solves several problems of modern nuclear power at once.

Thus, the decay products of thorium cannot be used to produce military radioactive materials. The possibility of such use serves as a political factor that keeps small countries from developing their own nuclear energy. Thorium fuel solves this problem once and for all.

Plasma traps can be useful not only in energy, but also in other peaceful industries - even in space. Now Rosatom and the Kurchatov Institute are working on components for an electrodeless plasma rocket engine for spacecraft and systems for plasma modification of materials. Russia's participation in the ITER project spurs the industry, which leads to the creation of new industries, which are already forming the basis for new Russian developments.