Atomic Power Plant


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atomic power plant

[ə′täm·ik ′pau̇·ər ‚plant]
(mechanical engineering)

Atomic Power Plant

 

a power plant in which atomic (nuclear) energy is converted into electrical energy. The energy generator in an atomic power plant is an atomic reactor. The heat liberated as a result of the chain reaction of nuclear fission of certain heavy elements is then transformed into electrical energy in the same way as in ordinary thermal electric power plants. In contrast to thermal electric power plants that operate on organic fuel, the atomic power plant operates on nuclear fuel (chiefly 233U, 235U, and 239Pu). In the fission of 1 g of uranium or plutonium isotopes, 22,500 kW-hr are liberated, which is equivalent to the energy contained in 2,800 kg of standard fuel. It has been established that the world’s energy resources of nuclear fuel (uranium, plutonium, and others) considerably exceed the energy resources of natural supplies of organic fuel (petroleum, coal, natural gas, and so on). This opens a broad perspective for the satisfaction of the rapidly growing need for fuel. In addition, it is necessary to take into account the ever-increasing volume of coal and petroleum consumption for the technological purposes of the worldwide chemical industry, which has become a serious competitor of thermal electric power plants. In spite of the discovery of new deposits of organic fuel and the development of methods for its extraction, there is a tendency in the world toward a relative increase of its cost. This creates most difficult conditions for nations that have limited supplies of organic fuels. There is a clear need for the very rapid development of atomic energy, which already occupies an appreciable place in the energy balance of a number of the world’s industrial nations.

The first atomic power plant in the world for experimental-industrial purposes, generating 5 mW of power, was put into service in the USSR on June 27, 1954, in the city of Obninsk. Until then the energy of the atomic nucleus was used chiefly for military purposes. The startup of the first atomic power plant marked the beginning of a new trend in power engineering, which had received recognition at the First International Scientific and Technical Conference on the Peaceful Uses of Atomic Energy (Geneva, August 1955).

In 1958 the first section of the Siberian Atomic Power Plant, with a capacity of 100 mW (total rated capacity, 600 mW) was put into operation. In the same year, construction of the Beloiarsk Industrial Atomic Power Plant was begun, and on Apr. 26, 1964, the generator of the first section (unit power, 100 mW) fed current into the Sverdlovsk power system. The second unit, with a capacity of 200 mW, went into operation in October 1967. The distinctive feature of the Beloiarsk Atomic Power Plant is the direct superheating of steam (until the requisite parameters are obtained) in the nuclear reactor, which made it possible to use ordinary modern turbines with almost no alterations.

In September 1964 the first section of the Novovoronezhskaia Atomic Power Plant, with a capacity of 210 mW, was put into service. The prime cost of 1 kW-hr of electrical energy (the most important economic indicator of the operation of any power plant) for this atomic power plant has been systematically reduced: it was 1.24 kopeks in 1965, 1.22 kopeks in 1966, 1.18 kopeks in 1967, and 0.94 kopeks in 1968. The first unit of the Novovoronezhskaia Atomic Power Plant was constructed not only for industrial use but also as a demonstration of the possibilities and advantages of atomic power engineering, its reliability, and the safety of atomic power plant operation. In November 1965 in the city of Melekess (Ul’ianovsk Oblast), construction was started on an atomic power plant with a water-moderated reactor of the “boiling water” type having a capacity of 50 mW; the reactor is assembled according to a single-loop network, which makes the layout of the plant easier. In December 1969 the second (350 = mW) section of the Novovoronezhskaia Atomic Power Plant was commissioned.

Abroad, the first atomic power plant for industrial purposes (46 mW) was put into operation in 1956 in Calder Hall (England). A 60-mW atomic power plant began operation a year later in Shippingport (USA).

The basic diagram of an atomic power plant with a water-cooled nuclear reactor is presented in Figure 1. The heat that is generated in the active zone of the reactor is removed by the water (coolant) of the first loop, which is pumped through the reactor by the circulation pump. The heated water from the reactor enters the heat exchanger (steam generator), where the heat obtained in the reactor is transferred to the water of the second loop. The water of the second loop is evaporated in the steam generator and the steam formed enters the turbine.

Figure 1. Basic diagram of an atomic power plant: (1) nuclear reactor, (2) circulation pump, (3) heat exchanger, (4) turbine, (5) electric-current generator.

Four types of thermal-neutron reactors are generally used for atomic power plants: (1) water-cooled with ordinary water as the moderator and coolant; (2) graphite-water, with aqueous coolant and graphite moderator; (3) heavy-water, with aqueous coolant and heavy water as the moderator; and (4) graphite-gaseous, with gaseous coolant and graphite moderator.

The choice of the appropriate type of reactor to be used is determined mainly by accumulated experience in reactor construction and also by the availability of the necessary industrial equipment, raw materials, and so on. In the USSR the graphite-water and water-moderated reactors have been constructed for the most part. In atomic power plants in the USA, water-moderated reactors have become most widely distributed. Graphite-gas reactors are used in England. Heavy-water reactors predominate in Canadian atomic power engineering.

Depending on the form and aggregate state of the coolant, one or another thermodynamic cycle of the atomic power plant is created. The choice of an upper temperature limit of the thermodynamic cycle is based on the maximum permissible temperature for the jackets of the fuel elements that contain the nuclear fuel, the permissible temperature of the nuclear fuel itself, and also the properties of the coolant accepted for the particular type of reactor. For an atomic power plant with a water-cooled thermal reactor, low-temperature steam cycles are preferred. Reactors with a gaseous coolant permit the use of comparatively more economical water vapor cycles with increased initial pressure and temperature. The thermal scheme of the atomic power plant in these two cases is built as a double loop: in the first loop the coolant is circulated; the second is a steam-water loop. With reactors using boiling-water or high-temperature gaseous coolants, a single-loop thermal atomic power plant is possible. In boiling reactors, the water boils in the active zone, the steam-water mixture obtained is separated, and the saturated steam is guided either directly into the turbine or is first returned to the active zone for superheating (see Figure 2). In high-temperature graphite-gas reactors, it is possible to use an ordinary gas turbine cycle. The reactor in this case fulfills the function of the combustion chamber.

Figure 2. Basic thermal diagram of an atomic power plant with nuclear superheating of steam (second unit of the Beloiarskaia Atomic Power Plant): (1) reactor, (2) evaporative channel, (3) steam superheating channel, (4) separator drum, (5) circulation pump, (6) de-aerator, (7) turbine, (8) condenser, (9) condensate pump, (10) low-pressure regenerative heater, (11) feed pump, (12) high-pressure regenerative heater, (13) electric-current generator.

During operation of the reactor, the concentration of fissionable isotopes in the nuclear fuel is gradually reduced, that is, the fuel elements burn out. Therefore, in time they must be replaced with fresh elements. The nuclear fuel is reloaded by means of remote-control mechanisms and apparatus. The exhausted fuel elements are transported to the cooling pond and then sent for retreatment.

The reactor and its facilities consist of the reactor proper and its biological shielding, the heat exchangers, the pumps or gas-blowing apparatus that creates circulation of the coolant, the piping system and hardware of the circulation loop, devices for the recharging of the nuclear fuel, and systems for special ventilation, emergency shutdown cooling, and so on.

Depending on its design, the reactor may have special features. In shell-type reactors the fuel elements and the moderator are located within a shell that bears the full pressure of the coolant; in channel reactors, the fuel elements—which are cooled by the coolant—are mounted in special tubes or channels that pass through the moderator, which is enclosed in a thin-walled casing. Such reactors are used in the USSR (the Siberian, Beloiarskaia, and other atomic power plants).

For the protection of atomic power plant personnel from radiation exposure, the reactor is surrounded by a biological shield made chiefly of concrete, water, and serpentine sand. The equipment of the reactor loop must be completely hermetic. A system is provided for monitoring the locations of possible coolant leakage, and measures are taken to prevent radioactive discharges and contamination of the atomic power plant installation and its environment caused by leakage and ruptures in the loop. The apparatus of the reactor loop is usually mounted in hermetic boxes that are separated from the rest of the atomic power plant installation by the biological shielding and are not serviced during reactor operation. Radioactive air and a small amount of coolant vapor caused by leaks from the loop are removed from the nonser-viced compartments of the atomic power plant by a special ventilation system in which cleaning filters and ageing gasholder tanks are provided for the elimination of possible atmospheric contamination. Dosimetric monitoring is observed for the fulfillment of the safety rules for atomic power plant personnel.

In case of failure in the cooling system of the reactor, rapid (within several seconds) extinguishing of the nuclear reaction is provided in order to eliminate superheating and breaking of the seal of the fuel element shells; the emergency shutdown cooling system has self-contained power sources.

The presence of biological shielding, a system of special ventilation, and emergency shutdown cooling, as well as dosimetric monitoring services, affords complete security to the atomic power plant service personnel against the harmful effects of radioactive exposure.

The equipment of the machine room of the atomic power plant is analogous to the equipment of the thermal power plant machine room. A specific feature of the majority of atomic power plants is the use of steam of comparatively low parameters, saturated or slightly superheated.

In this case, for the elimination of erosional damage of the blades of the last stages of the turbine caused by particles of moisture contained in the steam, separation devices are installed in the turbine. Sometimes it is necessary to use removal separators and intermediate steam superheaters. In connection with the fact that the coolant and the contaminants contained in it are activated in passing through the active zone of the reactor, the design of the machine-room equipment and cooling system of the turbine condenser in single-loop atomic power plants must completely eliminate the possibility of coolant leakage. For double-loop atomic power plants with high steam parameters, such demands on the machine-room equipment are not made.

Among the specific requirements for the layout of atomic power plant equipment are the minimal possible extent of services connected with radioactive agents, high rigidity of the foundations and supporting structures of the reactor, and a reliable system of building ventilation. In the reactor room of the Beloiarskaia Atomic Power Plant, with a channel graphite-water reactor, are located the reactor and biological shielding, reserve fuel elements, and monitoring apparatus. The atomic power plant is designed as an individual reactor-turbine unit. The turbine generators and their systems are located in the machine room. Between the machine and reactor rooms are located the auxiliary equipment and control systems of the plant.

The efficiency of an atomic power plant is determined by its primary performance factors—the reactor’s unit power, the efficiency and energy strength of the active zone, the burn-up fraction of the nuclear fuel, and the annual capacity factor of the atomic power plant. With the growth of the atomic power plant’s capacity, the unit investments in it (the cost of a standard kW) are reduced more sharply than in the case of thermal power plants. This is the main reason for the tendency toward the installation of large-scale atomic power plants with high unit block power. It is characteristic for the economics of atomic power plants that the share of the fuel component in the net cost of electrical energy being generated is 30–40 percent (for thermal power plants, it is 60–70 percent). Therefore, large-scale atomic power plants are most widespread in industrially developed regions with limited resources of ordinary fuels, and low-capacity plants are in regions that are remote or not readily accessible—for example, the atomic power plant in the settlement of Bilibino (Yakut ASSR), with a 12-mW standard unit. Part of the thermal power of this atomic power plant’s reactor (29 mW) is used for heat supply. In addition to the generation of electrical energy, atomic power plants are also used for the desalinization of seawater. Thus, the Shevchenko Atomic Power Plant (Kazakh SSR), with an electrical capacity of 150 mW, is designed for the desalinization by distillation of up to 150,000 tons of water per day from the Caspian Sea.

In the majority of industrially developed nations (the USSR, the USA, England, France, Canada, the Federal Republic of Germany, the German Democratic Republic, Japan, and others), it is forecasted that the power of the atomic power plants operating and under construction by 1980 will reach tens of gigawatts. According to the data of the UN Atomic Energy Commission, published in 1967, the installed power of all the atomic power plants in the world will reach 300 gigawatts by 1980.

In the Soviet Union a major program for the construction of large-scale energy units (up to 1,000 mW) with thermal-neutron reactors is being realized. In 1948–49 work was started on fast breeder reactors for industrial atomic power plants. The physical features of such reactors permit the realization of extensive breeding of nuclear fuel (conversion ratio of 1.3–1.7), which affords the possibility of using not only 235U but also the raw materials 238U and 232Th. In addition, fast breeder reactors do not contain moderators and have comparatively small dimensions and a large charge. This accounts for the tendency toward intensive development of fast reactors in the USSR. For research with fast reactors, the experimental and pilot reactors BR-1, BR-2, BR-3, BR-5, and BFS were successively constructed. The experience obtained determined the transition from research on model installations to the design and construction of the industrial fast-neutron atomic power plants in the city of Shevchenko and at the Beloiarskaia Atomic Power Plant (the BN-350 and BN-600, respectively). Research is being conducted on reactors for high-power atomic power plants—for example, in the city of Melekess a BOR-60 pilot reactor was constructed. Large-scale atomic power plants have been installed in a number of developing nations (India, Pakistan, and others).

At the Third International Scientific and Technical Conference on the Peaceful Uses of Atomic Energy (Geneva, 1964), it was noted that the broad application of nuclear energy had become a key problem for most countries. The Seventh World Conference on Power Engineering (MIREK-VII), which took place in Moscow in August 1968, affirmed the urgency of the problems of choosing the direction of development of nuclear energetics for the next phase (provisionally 1980–2000), when the atomic power plant will become one of the basic producers of electrical energy.

REFERENCES

Nekotorye voprosy iadernoi energetiki (collection of articles). Edited by M. A. Styrikovich. Moscow, 1959.
Kanaev, A. A. Atomnye energeticheskie ustanovki. Leningrad, 1961.
Kalafati, D. D. Termodinamicheskie tsikly atomnykh elektrostantsii. Moscow-Leningrad, 1963.
10 let Pervoi v mire atomnoi elektrostantsii SSSR (collection of articles). Moscow, 1964.
Sovetskaia atomnaia nauka i tekhnika (collection). Moscow, 1967.
Petros’iants, A. M. Atomnaia energetika nashikh dnei. Moscow, 1968.

S. P. KUZNETSOV

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