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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Nuclear power plant. History of invention and production
Directory / The history of technology, technology, objects around us Nuclear power plant (NPP) - a nuclear installation for the production of energy in specified modes and conditions of use, located within the territory defined by the project, in which a nuclear reactor (reactors) and a complex of necessary systems, devices, equipment and structures with the necessary workers are used for this purpose (personnel). The world's first nuclear power plant was built in the USSR nine years after the atomic bombing of Hiroshima. This most important event in the history of technology was preceded by feverish and intense work to create our own nuclear weapons. Scientific research was headed by a prominent scientist and talented organizer Igor Kurchatov.
In 1943, Kurchatov created his own research center in Moscow (at that time it was called Laboratory No. 2, and later it was transformed into the Institute of Atomic Energy). In this and some other laboratories, all the studies of American scientists were repeated in the shortest possible time, pure uranium and pure graphite were obtained. In December 1946, the first chain reaction was carried out here at the experimental nuclear uranium-graphite reactor F1. The power of this reactor barely reached 100 watts. However, it managed to obtain important data that served as the basis for the design of a large industrial reactor, the development of which was already in full swing. There was no experience in building such a reactor in the USSR. After some thought, Kurchatov decided to entrust this work to NIIkhimmash, which was led by Nikolai Dollezhal. Although Dollezhal was a pure mechanical chemist and had never studied nuclear physics, his knowledge proved to be very valuable. However, NIIkhimmash would not have been able to create a reactor on its own either. The work went successfully only after several other institutes joined it. The principle of operation and the structure of the Dollezhal reactor were generally clear: graphite blocks with channels for uranium blocks and control rods - neutron absorbers were placed in a metal case. The total mass of uranium had to reach the required value calculated by physicists, at which the sustained chain reaction of fission of uranium atoms began. As a result of the fission reaction of uranium nuclei, not only two fragments (two new nuclei) appeared, but also several neutrons. These neutrons of the first generation served to support the reaction, which resulted in neutrons of the second generation, the third, and so on. On average, for every thousand neutrons that have arisen, only a few were born not instantly, at the moment of fission, but a little later flew out of the fragments. The existence of these so-called delayed neutrons, which are a small detail in the process of fission of uranium, is decisive for the possibility of a controlled chain reaction. Some of them are delayed by a fraction of a second, others by seconds or more. The number of delayed neutrons is only 0% of their total number, however, they significantly (by about 75 times) slow down the rate of neutron flux growth and thereby facilitate the task of regulating the reactor power. It is during this time, by manipulating the rods absorbing neutrons, it is possible to intervene in the course of the reaction, slow it down or speed it up. Most neutrons are born simultaneously with fission, and in their short lifetime (about a hundred-thousandths of a second) it is impossible to influence the course of the reaction in any way, just as it is impossible to stop an atomic explosion that has already begun. Based on this information, Dollezhal's team was able to quickly cope with the task. Already in 1948, a plutonium plant with several industrial reactors was built, and in August 1949, the first Soviet atomic bomb was tested. After that, Kurchatov could pay more attention to the peaceful use of atomic energy. On his instructions, Feinberg and Dollezhal began to develop a design for a reactor for a nuclear power plant. The first did physical calculations, and the second - engineering. The fact that a nuclear reactor can be not only a producer of weapons-grade plutonium, but also a powerful power plant, became clear to its first creators. One of the external manifestations of the ongoing nuclear reaction, along with radioactive radiation, is a significant release of heat. In an atomic bomb, this heat is released instantly and serves as one of its damaging factors. In a reactor where the chain reaction is, as it were, in a smoldering state, intense heat release can continue for months and even years, and a few kilograms of uranium can release as much energy as is released during the combustion of several thousand tons of conventional fuel. Since Soviet physicists had already learned how to control a nuclear reaction, the problem of creating a power reactor was reduced to finding ways to remove heat from it. The experience gained during the experiments by Kurchatov was very valuable, but did not answer many questions. None of the reactors built by that time was a power reactor. In industrial reactors, thermal energy was not only unnecessary, but also harmful - it had to be removed, that is, to cool the uranium blocks. The problem of collecting and using the heat released during a nuclear reaction has not yet been considered either in the USSR or in the USA. The most important questions on the way of designing a power reactor for nuclear power plants were: what type of reactor (on fast or slow neutrons) would be most appropriate, what should be the neutron moderator (graphite or heavy water), what could serve as a coolant (water, gas or liquid metal) what should be its temperature and pressure. In addition, there were many other questions, such as materials, safety for personnel and increasing efficiency. In the end, Feinberg and Dollezhal settled on what had already been tested: they began to develop a slow neutron reactor with a graphite moderator and a water coolant. Good practical and theoretical experience has already been accumulated in their use. This predetermined the success of their project. In 1950, the technical council of the Ministry of Medium Machine Building chose a reactor developed by NIIkhimmash from several proposed options. Designing the power plant as a whole (it was decided to build it in Obninsk) was entrusted to one of the Leningrad research institutes, headed by Gutov. The planned capacity of the first nuclear power plant, 5000 kW, was largely chosen by chance. Just then, the MAES decommissioned a fully functional 5000 kW turbogenerator and transported it to Obninsk, which was under construction. Under it, they decided to design the entire nuclear power plant.
The power reactor was not so much an industrial as a scientific object. The construction of the nuclear power plant was directly supervised by the Obninsk Physics and Energy Laboratory, founded in 1947. In the early years, there were neither sufficient scientific forces nor the necessary equipment. Living conditions were also far from acceptable. The city was just being built. Unpaved streets were covered in spring and autumn with impassable mud, in which cars hopelessly got stuck. Most of the inhabitants huddled in wooden barracks and uncomfortable "Finnish" houses. The laboratory was located in buildings that were completely random and unsuitable for scientific purposes (one was a former children's colony, the other was the Morozovs' mansion). Electricity was generated by an old 500 kW steam turbine. When she stopped, the whole village and construction site plunged into darkness. The most complex calculations were made manually. However, scientists (many of whom had only recently returned from the front) endured hardships. The idea that they were designing and building the world's first nuclear power plant excited minds and aroused great enthusiasm. As for purely scientific problems, they were also very difficult. The fundamental difference between a power reactor and an industrial one was that in the second type of reactor, water served only as a coolant and did not carry any other functions. In addition, the excess heat removed by the water was such that its temperature did not quite reach the boiling point. Here, water was to act as an energy carrier, that is, to serve for the formation of steam capable of performing useful work. So, it was necessary to raise the temperature and pressure as much as possible. For the efficient operation of the turbogenerator, it was necessary at least to obtain steam with a temperature of over 200 degrees and a pressure of 12 atm (which, by the way, was very small for that time, but we decided to limit ourselves to these parameters for now).
During the construction, the design of an industrial reactor was taken as a basis. Only instead of uranium rods, uranium heat-removing elements - fuel elements were provided. The difference between them was that water flowed around the rod from the outside, while the fuel rod was a double-walled tube. Enriched uranium was located between the walls, and water flowed through the inner channel. Calculations have shown that with such a design it is much easier to heat it to the desired temperature. According to the draft drawings, the following appearance of the reactor loomed. In the middle part of the cylindrical body with a diameter of more than 1,5 m, there is an active zone - a graphite masonry about 170 cm high, penetrated by channels. Some of them were intended for fuel elements, others for rods that absorb neutrons and automatically maintain equilibrium at a given level. Cold water (which is actually not cold at all - its temperature is about 190 degrees) should flow into the lower part of the fuel rod assembly. After passing through the heat-removing elements and becoming 80 degrees hotter, it fell into the upper part of the assembly, and from there into the hot water collector. In order not to boil and turn into steam (this could cause abnormal operation of the reactor), it had to be under a pressure of 100 atm. From the collector, hot radioactive water flowed through pipes into a heat exchanger-steam generator, after which, after passing through a circular pump, it returned to the cold water collector. This current was called the first circuit. The coolant (water) circulated in it in a vicious circle, without penetrating outside. In the second circuit, water acted as a working fluid. Here she was non-radioactive and safe for others. Having heated up to 190 degrees in the heat exchanger and turned into steam with a pressure of 12 atm, it was supplied to the turbine, where it did its useful work. The steam leaving the turbine was to be condensed and sent back to the steam generator. The efficiency of the entire power plant was 17%. This seemingly easy-to-describe scheme was, in fact, technically very complex. The theory of the reactor did not exist then - it was born along with it. Fuel rods were a particularly complex element, the design of which largely depended on the efficiency of the entire installation. The processes that took place in them were very complex from all points of view: it was necessary to decide how and how to load uranium into them, to what extent it should be enriched, how to achieve circulation of water under high pressure, and how to ensure heat exchange. From several options, fuel elements developed by Vladimir Malykh were chosen - with uranium-molybdenum powder (uranium was enriched up to 5%), pressed with finely divided magnesium - this metal was supposed to create effective thermal contact of the uranium-molybdenum alloy with the fuel element wall.
Not only the filling of the fuel element, but also its cladding created a problem. The material of the heat-removing elements had to have strength, anti-corrosion resistance and should not change its properties under prolonged exposure to radiation. The best material from a chemical point of view - stainless steel - was not liked by physicists, since it strongly absorbed neutrons. In the end, Dollezhal nevertheless settled on steel. In order to compensate for its absorbing properties, it was decided to increase the percentage of enriched uranium (much later, a special zirconium alloy was developed for fuel elements that met all the necessary conditions).
The fabrication of fuel rods and the welding of stainless steel proved to be extremely difficult. Each fuel element had several seams, and there were 128 such fuel elements. Meanwhile, the requirements for the tightness of the seams were the highest - their rupture and the ingress of hot water under high pressure into the reactor core threatened disaster. One of the many institutes that have worked on this problem has been tasked with developing stainless steel welding technology. In the end, the job was successfully completed. The reactor was launched in May 1954, and in June of the same year, the nuclear power plant gave its first current. At the first nuclear power plant, the control system for the processes taking place in the reactor was carefully thought out. Devices were created for automatic and manual remote control of control rods, for emergency shutdown of the reactor, and devices for replacing fuel rods. It is known that a nuclear reaction begins only when a certain critical mass of the fissile material is reached. However, during the operation of the reactor, nuclear fuel burns out. Therefore, it is necessary to calculate a significant amount of fuel in order to ensure the operation of the reactor for a more or less significant time. The influence of this supercritical reserve on the course of the reaction was compensated by special rods that absorb excess neutrons. If it was necessary to increase the power of the reactor (as the fuel burned out), the control rods were somewhat extended from the reactor core and installed in a position where the reactor was on the verge of a chain reaction and active fission of uranium nuclei was taking place. Finally, emergency protection rods were provided, the lowering of which into the core instantly extinguished the nuclear reaction. Author: Ryzhov K.V.
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