Дата публикации: 19 августа 2021
Автор(ы): Academician Yevgeny VELIKHOV →
Публикатор: Научная библиотека Порталус
Рубрика: АНГЛИЙСКИЙ ЯЗЫК →
Источник: (c) Science in Russia, №1, 2010, C.37-41 →
Номер публикации: №1629378878
Academician Yevgeny VELIKHOV, (c)
That was a historic event as government representatives of China, India, Japan, Republic of Korea, Russia, United States and European Union met in Paris, France, on the 21st of November 2006 to sign an agreement on the funding of the International Thermonuclear Experimental Reactor (ITER). This major international project involving scientists and engineers of many countries is now under construction at Caradache, a small town 70 km south of Marseilles, France. This is the subject of an article contributed by Acad. Yevgeny Velikhov and Dr. Sergey Mirnov to the VESTNIK of MEI (No. 4, 2009), a journal published by the Moscow Energy Institute. By permission of the VESTNIK of MEI editors we follow with an abridged version of this article.
TRIAL AND ERROR
Power engineering scientists view the "finish line" notion differently. Thus, Thomas Edison (1847-1931), the inventor of electric lighting, likewise invented the first practical incandescent lamp, lampholder (we are still using it), electricity supply networks and even substation generators. None the less it took as good as half a century to make electric lighting a vital part of our everyday life: evidently, as Acad. Lev Artsimovich put it (with respect to thermonuclear combustion though), there was no "absolute necessity" of that.
Carrying on this analogy, we can say: present-day plasma physics experts still zero in on the problem of the
Schematic diagram of a tokamak reactor.
"filament" in their electric light "bulb" and suppose its technical solution would be a finish-line buck they could pass on into the hands of other scientists closer to practical power engineering and capable of getting down to the "lamp holder and base" problems. This matter ought to be the head and purpose of the ITER project to provide for quasistationary (400 to 1000s) thermonuclear combustion of a deuterium-tritium (DT) mixture taken in the 50:50% ratio—the same one that was used with much success in the hydrogen bombs. Naturally the "lampholder-base" problems will not be scrapped either. Yet the ultimate task for ITER is to prolong the time of a thermonuclear explosion from microseconds (in the H-bomb) to hours and days.
This is to be done in thermonuclear reactors. Their chief function is to achieve plasma confinement by means of magnetic fields, that is insulate the DT mixture heated to 100 mln degrees Celsius from the material walls of a setup (note: the temperature in the center of the sun is about 15 mln °C!). The substance at such superstellar temperatures is fully ionized to plasma. The problem of its thermoinsulation (confinement, or containment) has been the main "intrigue", so to say, in controlled nuclear fusion over the last fifty years.
Thus far the best results have been achieved in what we call tokamaks (toroidal chambers, or doughnuts cum magnetic field). In this country their idea was substantiated and developed in the early 1950s by Acads. Andrey Sakharov and Igor Tamm, while its technical realization, as the first high-temperature thermonuclear plasma was obtained (State Prize of the USSR, 1971), was accomplished at the Kurchatov Institute of Atomic Energy (the Russian Research Center "Kurchatov Institute" today) under Lev Artsimovich at the end of the 1960s and in the beginning of the 1970s. A mix of heavy hydrogen isotopes, deuterium and tritium, is heated within a reactor's toroidal chamber (fixed "tight" midway) to the temperature of thermonuclear combustion by a high-current (up to 20 MA) gas discharge fed from an ordinary transformer. Here the plasma is in the role of a secondary short-circuited coil. Thus confined ("suspended"), the plasma will be kept from "breaking" and clinging to the chamber's walls, and it will be stabilized by poloidal and toroidal magnetic fields generated with the aid of special windings. The closed spiral configuration thus obtained turns into a well-nigh ideal plasma trap and protects the chamber material walls against the action of superhigh temperatures. The main thermonuclear product—fast (14 MeV) neutrons-is converted to heat and vapor in a special device, the blanket, enclosing the toroidal chamber.
The idea caught on worldwide. And, as it often happens, the pupils upstaged their teachers. Already in the late 1970s American nuclear physicists, using a PLT doughnut, obtained plasma of the reactor scale temperatures (70 mln oC); and on October 30, 1997, in an experiment involving a DT mixture in the Joint European Torus (JET) in England-its chamber, about 2 m across and 4 m tall, maximum current, 7.5 MA, induction of the toroidal magnetic field, up to 3.5 TL-a 17 MW power value was obtained, which correlates with a level of power applied to the plasma for sustaining thermonuclear combustion. The many protective plates of this setup were made of graphite composites similar to those used in space shuttles; these plates were coated with a thin layer of beryllium against corrosion. Thus, an essential frontier was reached in controlled thermonuclear fusion, a cross-over point when thermal losses and energy output are equalized. True, this record result was achieved only in the transitional pulse-driven mode for about 1 s. No more than "striking thermonuclear matches"!
Stationary or quasistationary combustion (on for many seconds) is what is needed for a power reactor. Such kind of combustion lasting for dozens of seconds has been realized at some large doughnuts; however, the heat losses exceed considerably the energy yield (which should be fivefold as high). The thing is that DT fusion produces a fast neutron (14 MeV), and a sufficiently energized (3.6 MeV) ion 4He (a-particle) "trapped", unlike a free ion, in a magnetic field and not capable of escaping the plasma. With deceleration its energy should heat the plasma within. Once the energy of internal heating, equal to 1/5 of the total nuclear yield, has compensated the heat losses, thermonuclear combustion will become self-sustaining. Thereupon external heating systems—beams of high-energy neutron atoms, and HF and SHF generators-could be turned off. This will make it possible to streamline the reactor and cut its costs. This moment of truth is what we call "ignition". It will occur as the nuclear fusion power has attained to 500 MW.
So, the big ITER project is going to be the next logical step of the tokamak program to merge the ideas of ignition and stationary thermonuclear fusion on the basis of fundamental achievements of physics and available technologies.
FACT, NOT FICTION
Even the first tentative estimates of the ITER project ran into 10 billion US dollars. Since the total cost of the world's biggest tokamaks in operation at the end of the 1980s was not above 0.5 bln dollars, there could be no doubt it was advisable to make ITER a cooperative international venture. Our country advanced the idea of such cooperation in 1985, and it got support first from the United States, then from Japan and the European Community. The first version, on which a joint multinational collective of physicists and engineers had been working for five years and which cost about 1.5 bln dollars, was completed in 1998.
It was a pioneering undertaking—the blueprint of a quasistationary thermonuclear reactor with a rated thermal capacity of 1.5 GW designed relative to state-of-the-art technologies. Some key elements of the setup were manufactured life-size and tested. All drawings done according to Western standards could be handed directly to manufacturers. However, the total bill, comparable to the preliminary estimates (7.5 bln dollars in ten years) triggered a spate of critical responses by reason of "exorbitant costs". The Americans suggested to halve it. The other cofounders liked the idea, and the designers turned to the cost-cutting job. But this did not save the alliance. US Congress deemed further American participation was running counter to US national interests, and the Americans walked out. The foursome became a trio.
Yet the cooperative project was still alive. The truncated 5 bln dollar project was completed in 2001. Its technical parameters were as follows: the chamber, ~8 meters; cross-section, ~4 m; induction of the toroidal magnetic field along the chamber's axis, 6 T1; plasma current, 18 MA; primary transformer and poloidal field windings were superconducting. Such parameters made it essentially possible to get a 400s thermonuclear combustion momentum. Its power output was to reach 500 MW, or higher than energy expenditures involved in sustaining combustion. An array of blanket modules were
provided for studying the problems of tritium yield and utilization of the energy of fast neutrons. Beryllium plates were to protect them against the direct effect of plasma.
The cofounders of the project (European Union, Japan, Russia) approved the work done. But then the project was... shelved for as long as four years. They, the cofounders, were in a quandary: where to build? In France or in Japan? Both countries had an advanced nuclear industry, with 60 to 70 percent of electricity generated by nuclear power stations. Getting a high-cost international order meant a good incentive for further technological development in the home countries. Meanwhile China, South Korea and India joined the ITER club, and the United States returned to the fold. Yet shuttle diplomacy took a lot of time thus putting off the time of power production through thermonuclear fusion.
Maybe the whole thing is not as urgent and could wait? They say: the West is in for low-cost Iraqi petroleum once democracy has been established there. And yet there are well-grounded fears there will be no oil El Dorado even if democratic rule takes in all the Near and Middle East. As a matter of fact, just 15 percent of the population in economically advanced countries was consuming 85 percent of the world petroleum resources at the close of the 20th century. All inequalities, however, tend to equalize. China's economic advancement is an ocular example. The Chinese ideal of the 1970s was a sewing machine, bicycle and television set; today the automobile has moved in. China, that's 1.5 billion people. And what about India, Africa?..
Political "heavyweights" descended into the arena at the closing stage of the ITER talks held in the spring of 2005: the French president and the prime-minister of Japan. A long-awaited consensus was reached: ITER was to be built in France, while Japan would be handling high-cost orders and training most of the experts. Certain details are yet to be specified; but the very fact that the building side was decided upon is a great victory that the ITER pool had been working for as long as twenty years. Europe is to shoulder half of the total bill, while India, Japan, Russia, South Korea and the United States, 10 percent each.
Now, what will humanity get from controlled thermonuclear fusion? It is obvious to experts: DT power engineering is a natural part of the nuclear industry at large. A fast neutron energized to 14 MeV and the inevitable activation of reactor structures is what is common. More than that, the prospect of using DT fusion
1:50 scale model of ITER.
Cut-away view of an ITER computer model.
While all of the ITER project can fit into one shed now, it will be a real town in ten years' time.
both for power production and for the "reburning" of radioactive wastes produced by nuclear fission reactors is on the anvil now. The aim is to upgrade the ecological indicators of contemporary power engineering. All the component elements needed for that are there, and it would not be so much difficult to bring them together.
Nuclear fusion has infinite resources in practical terms. This is likewise true of deuterium (a deuterium atom is per every 7,000 atoms of hydrogen in ordinary water); as to lithium (which goes to make the other component of the nuclear fuel), it is of wide occurrence in natural conditions. According to informed expert opinion, nuclear fusion power will be by about two orders safer than the energy of uranium fission, largely due to the absence of gaseous and liquid radioactive waste. Solid waste is thought to pose no major threat. Unlike nuclear fission, nuclear fusion is in practical terms inertless. Emergencies similar to the disaster at the Chernobyl Atomic Power Station in 1986 are absolutely ruled out. And last, no uranium is needed for thermonuclear fusion. If complemented by uranium or thorium ore in hybrid setups, it offers great prospects both in reactor safety and in the resource supply of conventional nuclear energetics operating on 239Pu and 233U.
Can DT setups be used for arms production? Yes, like any facilities involving neutrons. International control will be needed therefore.
What is the Russian input in the ITER project? Fifty million US dollars annually for ten years, as long as its construction is underway. It is big money for our home science, but not as big as what is needed for the upkeep of a good football team. This money will be expended at home in offsets.
But how will Russia stand to gain from the deal? The main benefit—and we felt it already at the ITER gestation stage—access to high technologies and incentives for their development at home. True, the "proliferation" of high-tech technologies may rub some of our allies the wrong way.
When could controlled DT fusion be applied on a wide scale? Now, ITER is an experimental reactor built on the basis of today's (or rather, yesterday's) technologies well-tested in practice. But it is not a prototype of a power reactor yet. Its aim is to demonstrate the practical possibility of thermonuclear ignition and stationary combustion. Power generation will be something for the next, going (demonstrative) reactor whose contours are yet obscure and will be defined in course of the present project. Yet certain putative key technologies are being discussed and designed, with some of them tested. Quite possible, a commercial reactor will be one of ITER modifications, which would also mean economy in time and money. Yet even given most favorable conditions, the creation of the first power reactor would take at least 20 to 30 years. The countup should begin as the ITER reactor is onstream. The main task in order now is to ensure stationary thermonuclear combustion and a longterm resource base. It is important to make a new energy source competitive with conventional ones. If this objective is reached, the demonstrative going reactor with its rated capacity equal to that of ITER— equipped in addition with a thorium blanket—can reach a power level as high as 1 GW and produce as much as 2 tons of fuel yearly for nuclear power setups operating on thermal neutrons (235U). This fuel could add yet another 2 GW to the capacity of conventional fission reactors. The deposits of thorium in this country are much higher than those of uranium.
Опубликовано на Порталусе 19 августа 2021 года
Ваше мнение ?