Managed thermonuclear fusion is the blue dream of physicists and energy companies, which they cherish for decades. Making an artificial Sun in a cage is a great idea. “But the problem is that we do not know how to create such a box, ” said Nobel laureate Pierre Gilles de Gennes in 1991. However, by the middle of 2018, we already know how. And we even build. The best minds of the world are working on the project of the international experimental thermonuclear reactor ITER – the most ambitious and expensive experiment of modern science.
Such a reactor costs five times more than the Large Hadron Collider. Hundreds of scientists around the world work on the project. Its financing can easily exceed 19 billion euros, and the first plasma reactor will be allowed only in December 2025. And despite the constant delays, technological difficulties, insufficient funding from individual participating countries, the world’s largest thermonuclear “perpetual motion machine” is being built. He has much more advantages than disadvantages. Which ones? The story of the most ambitious scientific construction of modernity begins with the theory.
What is a tokamak?
Under the influence of huge temperatures and gravitation in the depths of our Sun and other stars, thermonuclear fusion takes place. The hydrogen nuclei collide, form heavier helium atoms, and at the same time release neutrons and a huge amount of energy.
Modern science has come to the conclusion that at the lowest initial temperature, the reaction between the hydrogen isotopes-deuterium and tritium-produces the greatest amount of energy. But for this three conditions are important: high temperature (about 150 million degrees Celsius), high plasma density and high retention time.
The point is that we can not create such a colossal density as the Sun does. It remains only to heat the gas to the state of plasma by means of ultrahigh temperatures. But no material is able to make contact with such a hot plasma. To do this, Academician Andrei Sakharov (from the submission of Oleg Lavrentiev) in the 1950s suggested using a toroidal (in the form of a hollow donut) chamber with a magnetic field that would hold the plasma. Later, the term came up with a tokamak.
Modern power plants, burning fossil fuels, convert mechanical power (torsion of turbines, for example) into electricity. Tokamaks will use the energy of synthesis, absorbed in the form of heat by the walls of the device, for heating and producing steam, which will turn the turbines.
Small experimental tokamaks were built around the world. And they successfully proved that a person can create a high-temperature plasma and hold it for a while in a stable state. But it is still far from industrial designs.
Advantages and disadvantages of thermonuclear reactors
Typical nuclear reactors operate on dozens of tons of radioactive fuel (which eventually turn into tens of tons of radioactive waste), whereas a thermonuclear reactor only needs hundreds of grams of tritium and deuterium. The first can be produced at the reactor itself: the neutrons released during the synthesis will act on the walls of the reactor with lithium impurities, from which tritium appears. The reserves of lithium will last for thousands of years. In deuterium, too, there will be no shortage – it is produced in the world by tens of thousands of tons per year.
The thermonuclear reactor does not produce greenhouse gas emissions, which is typical for fossil fuels. A by-product in the form of helium-4 is a harmless inert gas.
In addition, thermonuclear reactors are safe. In any catastrophe, the thermonuclear reaction simply stops without any serious consequences for the environment or personnel, as there will be nothing to support the synthesis reaction: too much greenhouse conditions are necessary for it.
However, thermonuclear reactors have disadvantages. First of all, this is the banal complexity of launching a self-sustaining reaction. She needs a deep vacuum. Complex systems of magnetic confinement require huge superconducting magnetic coils.
And do not forget about radiation. Despite some stereotypes about the harmlessness of thermonuclear reactors, the bombardment of their surroundings by the neutrons produced during the synthesis is not canceled. This bombardment leads to radiation. Therefore, maintenance of the reactor must be carried out remotely. Looking ahead, we will say that after the launch of the ITER tokamak, the robots will be engaged directly in servicing the ITER tokamak.
In addition, radioactive tritium can be dangerous when ingested. True, it will be enough to take care of its proper storage and create security barriers on all possible ways of its distribution in the event of an accident. In addition, the half-life of tritium is 12 years.
When the necessary minimum foundation of the theory is laid, you can go to the hero of the article.
The most ambitious project of our time
In 1985 in Geneva the first personal meeting between the heads of the USSR and the USA took place for many years. Before that, the cold war reached its peak: the superpowers boycotted the Olympics, increased their nuclear capabilities and did not intend to negotiate any negotiations. This summit of the two countries on the neutral territory is noteworthy and another important circumstance. During his time, the Secretary General of the CPSU Central Committee, Mikhail Gorbachev, proposed the implementation of a joint international project to develop thermonuclear energy for peaceful purposes.
A year later, an agreement was reached between the American, Soviet, European and Japanese scientists on the project, the conceptual design of a large thermonuclear complex ITER began. The engineering details were delayed, the US then left and then returned to the project, with it eventually joined China, South Korea and India. Participants shared responsibilities for financing and direct works, and in 2010 the foundation pit for the foundation of the future complex was finally launched. He decided to build in the south of France near the city of Aix-en-Provence.
So what is ITER? This is a huge scientific experiment and an ambitious energy project for the construction of the largest tokamak in the world. The construction must prove the possibility of commercial use of the thermonuclear reactor, and also solve the emerging physical and technological problems along this path.
What does the ITER reactor consist of?
The Tokamak is a toroidal vacuum chamber with magnetic coils and a cryostat weighing 23,000 tons. As already clear from the definition, we have a camera. Deep vacuum chamber. In the case of ITER, this will be 850 cubic meters of free chamber volume, in which at the start there will be only 0.1 grams of a mixture of deuterium and tritium.
On the inner walls of the camera there are special modules called blankets. Water circulates inside them. The free neutrons that escape from the plasma get into these blankets and are decelerated by water. Because of what it is heated. Blankets themselves protect the rest of the scale from the thermal, X-ray and already mentioned neutron radiation from the plasma.
Such a system is necessary in order to extend the life of the reactor. Each blanket weighs about 4.5 tons, it will be changed by a robotic arm approximately every 5-10 years, since this first line of defense will be subject to evaporation and neutron radiation.
But this is not all. Intracameral equipment, thermocouples, accelerometers, already mentioned 440 blocks of blanket system, cooling system, shielding unit, divertor, magnetic system of 48 elements, high-frequency plasma heaters, injector of neutral atoms, etc. are attached to the chamber. And all this is inside a huge cryostat height of 30 meters, having the same diameter and volume of 16 thousand cubic meters. The cryostat guarantees a deep vacuum and an ultracold temperature for the tokamak chamber and superconducting magnets, which are cooled by liquid helium to a temperature of -269 degrees Celsius.
The production of all this equipment is divided among the participating countries. For example, over part of the blankets are working in Russia, over the cryostat body – in India, over the vacuum chamber segments – in Europe and Korea.
But this is by no means a fast process. Besides, the designers do not have the right to make a mistake. The ITER team first simulates loads and requirements for design elements, they are tested on stands (for example, under the influence of plasma guns, like a divertor), improve and modify, collect prototypes and again test before issuing the final element.
But it is one thing to gather. And it’s quite another to serve all this. Due to the high level of radiation, access to the reactor has been ordered. To support it, a whole family of robotic systems has been developed. The part will change the divertor’s blankets and cassettes (weighing under 10 tons), some will be remotely controlled to eliminate accidents, some will be based in the pockets of the vacuum chamber with HD cameras and laser scanners for quick inspection. And all this must be done in a vacuum, in a narrow space, with high accuracy and in a clear interaction with all systems. The task is more complicated than repairing the ISS.
And this is only part of the equipment of the reactor itself. Add the building of the cryogenic plant, where they will produce liquid nitrogen and helium, a rectifier building of the magnetic system with transformers, cooling system pipelines (diameter of 2 meters), a heat recovery system with 10 fan cooling towers and much more. All this goes to billions.
Why do I need ITER and who pays for it?
The ITER Tokamak will be the first thermonuclear reactor that will generate more energy than necessary to heat the plasma itself. In addition, it will be able to maintain it in a stable state much longer than the current installations. Scientists say that it is for this purpose that such a large-scale project is needed.
With the help of such a reactor, experts are going to bridge the gap between the current small experimental installations and fusion power plants of the future. For example, a record on thermonuclear power was established in 1997 on a tokamak in Britain – 16 MW with 24 MW spent, whereas ITER was designed with a target of 500 MW of thermonuclear power from 50 MW of input thermal energy.
The tokamak will test the heating, control, diagnostics, cryogenics and remote maintenance technologies, that is, all the techniques required for an industrial thermonuclear reactor.
Volumes of world production of tritium will not be enough for future power plants. So ITER will also work out the technology of a multiplying blanket containing lithium. From it, under the action of thermonuclear neutrons, tritium will be synthesized.
However, do not forget that this is also expensive, but an experiment. The Tokamak will not be equipped with turbines or other systems for converting heat to electricity. That is, commercial emissions in the form of direct generation of energy will not. Why? Because this would only complicate the project from an engineering point of view and make it even more expensive.
The financing scheme is rather confusing. At the stage of construction, the creation of the reactor and other systems of the complex, about 45% of the costs are borne by the EU countries, the remaining participants – by 9%. However, most of the contributions are “nature”. Most components are shipped directly to ITER from participating countries.
They arrive in France by sea, and from the port to the construction site are delivered on the road, specially redesigned by the French government. At 104 km “Ways ITER” the country spent 110 million euros and 4 years of work. The route was expanded and strengthened. The fact is that until 2021 250 convoys with huge cargo will pass through it. The heaviest details reach 900 tons, the highest – 10 meters, the longest – 33 meters.
While ITER is not put into operation. However, there is already a project for the DEMO power plant on thermonuclear fusion, whose task is to demonstrate the attractiveness of the commercial use of technology. This complex should be continuously (and not pulsed, like ITER) to generate 2 GW of energy.
The timing of the implementation of the new global project depends on the success of ITER, but according to the plan for 2012, the first DEMO launch will not occur until 2044.