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Nuclear power station

Nuclear power station
The world's first nuclear power plant was built in the USSR, nine years after the atomic bombing of Hiroshima. This is the most important in the history of the art event was preceded by feverish and hard work to build their own nuclear weapons. This work is led by a prominent scientist and talented organizer Igor Kurchatov. In 1943 Kurchatov established its research center in Moscow (at the time it was called the Laboratory number 2, and was later transformed into the Institute of Atomic Energy). In this and in some other laboratory as soon as possible all the studies were repeated by American scientists, produced pure uranium and pure graphite. In December 1946, here it is the first chain reaction on the experimental nuclear uranium-graphite reactor F1 was carried out. The power of this reactor was barely 100 watts. However, it managed to obtain important data that served as the basis for the design of large industrial reactors, the development of which is already in full swing.

Experience on the construction of such a reactor in the USSR there was no. After some thought, Kurchatov decided to entrust this work NIICHIMMASH, led by Nikolai Dollezhal. Although Dollezhal was clean chemist machine builder and never engaged in nuclear physics, his knowledge was very valuable. However, on its own NIICHIMMASH also not managed to create a reactor. The work went successfully only after it has joined several other institutions. Principle and Dollezhal reactor unit were in general are clear: in a metal enclosure placed graphite blocks with channels for uranium blocks and control rods - neutron poisons. The total mass of uranium was calculated by physicists to achieve the required value at which begins to support a chain reaction of fission of uranium atoms. The reaction of uranium fission occurs not only two fragments (two new kernel), but also several neutrons These neutrons were the first generation and to maintain the reaction, resulting in the second generation of neutrons, the third and so on. On average, for every thousand neutrons emerged only a few were born not instantly, at the time of the division, and a little later flew out of the fragments. The existence of these so-called delayed neutrons, which are small parts in the process of fission of uranium, is crucial for the feasibility of a controlled chain reaction. Some of them are late for a split second, the other - on the second, and more. Number of delayed neutrons is only 0, 75% of the total, but they are considerably (about 150 times) slow down the rate of rise of the neutron flux and thereby facilitate the task of regulating the reactor power. It was during this time, manipulating the rods absorb neutrons, it is possible to intervene in the course of the reaction, slow down or accelerate it. Most neutrons are born simultaneously with the division, and in a short time of their life (about one hundred thousandth of a second) can not in any way affect the course of the reaction, it is impossible to stop the already started a nuclear explosion. Based on this information, the team was able to quickly Dollezhal cope with the task. For plutonium plant with several industrial reactors was built in 1948, and the first Soviet atomic bomb was tested in August 1949.

After that, Kurchatov could pay more attention to the peaceful use of nuclear energy. On his behalf, Feinberg and Dollezhal reactor started developing a project for a nuclear power plant. The first to do physical calculations, and the second - engineering. The fact that the nuclear reactor can be not only a producer of weapons-grade plutonium, but also a powerful power plant, first became clear to its founders. One of the external manifestations occurring nuclear reaction along with the radioactive radiation is a significant release of heat. The atomic bomb, this heat is released instantaneously and is one of the factors affecting it. In the reactor, where the chain reaction is, as it were in a state of smoldering, intense heat can last months or even years, and several kilograms of uranium can allocate the same amount of energy as when burned emit thousands of tons of conventional fuel. Since the Soviet physicists have learned to control the nuclear reaction, the problem of creating a power reactor was reduced to finding ways of removal of heat from it. The experience gained in the course of experiments Kurchatov, was very valuable, but did not give an answer to many questions. None of the built by this time was not energy reactors. heat was not only unnecessary in industrial reactors, but also harmful - it had to take, that is to cool the uranium blocks. The problem of collection and use of the heat released during nuclear reactions, either in the USSR or have not been reviewed in the United States.

The most important issues in the way of a power reactor design for nuclear power plants have been: what type of reactor (fast or slow neutrons) will be the most expedient that there should be a neutron moderator (graphite or heavy water), which can serve as a coolant (water, gas or liquid metal) what should be the temperature and pressure. In addition, there were many other issues, such as the materials for the safety of staff and an increase in efficiency. In the end, Feinberg and Dollezhal settled on what has already been tried: they began to develop on slow neutron reactor with a graphite moderator and water coolant. Their use has been gained a good practical and theoretical experience. This predetermined the success of their project. In 1950, the Technical Council of the Ministry of Medium Machine Building of several proposed options chosen reactor designed NIICHIMMASH. Design a power plant as a whole (it was decided to build in Obninsk) was assigned to one of the Leningrad Research Institute, headed Gutov. The planned capacity of the first nuclear power plant 5000 kW - in many respects has been chosen randomly. Just then MAES copied quite efficient turbine generator 5000 kW and has forwarded it to the construction Obninsk. Under it, and we decided to design the entire plant.

The energy reactor was not so much industrial as research object. Directly supervised the construction of nuclear power plants Obninsk Physics and Energy laboratory, founded in 1947. In the early years there was not sufficient scientific strength nor the necessary equipment. The living conditions were far from acceptable. City just built. Dirt streets were covered in spring and autumn thick mud, which sank hopelessly machine. Most of the inhabitants huddled in plank barracks and uncomfortable "Finnish" houses. The laboratory was located in a completely random and unsuitable buildings for scientific purposes (one - a former children's colony, the other - the Morozov mansion). Electricity is produced by the old steam turbine of 500 kW. When she stopped, the whole village and building plunged into darkness. Complicated calculations were performed manually. However, scientists (many of whom have only recently returned from the front) with firmness transferred difficulties. The idea that they design and build the first nuclear power plant dominates the minds and aroused great enthusiasm in the world.

With regard to purely scientific problems, they were also very difficult. The fundamental difference from the power reactor industry was the fact that the second type of reactor coolant water is served only, and no other functions are not carried. In addition, excess heat removed with water, were such that the temperature is fairly did not reach the boiling point. Here the water was to act as a source of energy that is used to generate steam that can do useful work. So, as much as possible was required to raise the temperature and pressure. For efficient operation of the turbine generator needed to at least get steam with a temperature of over 200 degrees and a pressure of 12 bar (which, incidentally, was at that time very little, but have decided to restrict these parameters).

During the construction of the basis for the industrial design of the reactor was taken. Only instead of uranium rods were provided teplovyvodyaschie uranium elements - fuel rods. The difference between them was that the water flowed outside the rod, the fuel element is represented by a double-walled tube. Between the walls located enriched uranium, and the internal channel water flows. Calculations have shown that to heat it to the desired temperature in a much simpler design. By sketch drawings loomed following the appearance of the reactor. In the middle part of the cylindrical body with a diameter of more than 1, 5 meters is the active zone - graphite stack height of about 170 cm, filled with channels. Some of them were intended for fuel rods, while others - for the rods that absorb neutrons and automatically maintain a balance at a given level. In the lower part of the fuel rod assembly should flow cold water (which is actually not cold - the temperature is about 190 degrees). Going through teplovyvodyaschie elements and become 80 degrees hotter it got to the top of the assembly, and then - in hot water collector. In order not to boil and turn to steam (this could cause abnormal operation of the reactor), it was supposed to be under the pressure of 100 atm. From the reservoir the hot radioactive water flowing through the tubes in a steam generator heat exchanger, after which, after passing through a circulation pump, returned to the cold water reservoir. This current is called the primary circuit. The coolant (water) circulated it in circles, without getting out. In the second loop Water acted in the role of the working fluid. Here, it was non-radioactive and is not dangerous to others. Warmed in a heat exchanger to 190 degrees and turned into steam with a pressure of 12 bar, it was applied to the turbine, where it produced a useful work. Who left the turbine steam was condensed and sent back to the steam generator. Efficiency of the entire power plant was 17%.

This seemingly simple to describe the scheme actually was technically very challenging. Theories of the reactor did not exist - she was born with it. Especially difficult element were fuel rods from the device which is largely dependent on the efficiency of the entire installation. Processes occurring in them, have been very difficult from every point of view: to decide how, and how to load them uranium to the extent necessary to enrich it, how to achieve water circulation, is under high pressure, and how to provide heat. Of the several options were selected fuel rods, designed by Vladimir Small - a uranium-molybdenum powder (uranium was enriched to 5%), compressed with the finely divided magnesium - the metal had to create an effective thermal contact between the uranium-molybdenum alloy with a wall of the fuel element.

Not only the filling of the fuel element, and its shell created a problem. Material teplovyvodyaschih elements had to have strength, anti-corrosion resistance and should not change its properties under prolonged exposure to radiation. The best from the chemical point of view the material - stainless steel - not like physicists, because it strongly absorbs neutrons. In the end, Dollezhal still focused on the steel. To compensate for its absorbent properties, it was decided to increase the percentage of highly enriched uranium (which satisfies all the necessary conditions for many later special zirconium alloy has been developed for the fuel rods). Production of fuel rods and stainless steel welding proved to be extremely difficult. Each fuel rod had a few stitches, and these fuel rods was 128. Meanwhile, to the joints tightness requirements were very high - they break and getting hot water at high pressure into the reactor core threatened disaster. One of the many institutions that have worked on this issue, has been charged with stainless steel welding technology development. After all the work has been performed successfully. The reactor was started up in May 1954, and in June the same year, the first nuclear power plant given current.

The first nuclear power plant was a carefully thought out control system of processes occurring in the reactor. devices have been designed for automatic and manual remote control rods for the emergency shutdown of the reactor, devices for replacement of fuel elements. It is known that a nuclear reaction begins only when a certain critical mass of fissile material. However, during operation of the reactor nuclear fuel is burned. It is therefore necessary to calculate a substantial amount of fuel to ensure that operation of the reactor more or less considerable time. Influence of supercritical stock on the reaction was compensated by special rods that absorb excess neutrons. If required to increase capacity of the reactor (as the combustion fuel) control rods put forward more from the reactor core and installed in such a position, when the reactor is on the verge chain reaction and is active fission of uranium. Finally, it has provided emergency protection rods, which are sinking into the core instantly extinguished nuclear reaction.

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