Sealed enclosure ( tight enclosure [1] ; containment [2] [3] ; pressurized [2] ; containment [2] ; containment from English containment [2] ) is a passive safety system for nuclear power reactors , the main function of which is to prevent release of radioactive substances into the environment in severe accidents. The containment is a massive structure of a special design, which houses the main equipment of the reactor installation . The containment is the most characteristic in terms of architecture and the most important from the point of view of safety building of nuclear power plants , the last physical barrier to the spread of radioactive materials and ionizing radiation [4] [5] [6] .
Almost all power units built over the past few decades are equipped with protective shells. Their use is necessary for protection in the event of an internal accident with the rupture of large pipelines and loss of coolant ( English LOCA, Loss-of-coolant accident ), as well as in the event of external events: earthquakes , tsunamis , hurricanes , tornadoes , airplanes , explosions , rockets strokes, etc. [4] [7] .
The containment shell is designed to perform its functions, taking into account all possible mechanical, thermal and chemical influences that are a consequence of the coolant expiration and core melting. Most often, containment shells have auxiliary equipment: localizing safety systems for steam condensation and thus reducing pressure, special ventilation systems equipped with filters for cleaning radioactive isotopes of iodine , cesium and other fission products [8] [9] .
Depending on the type of reactor and specific external threats (for example, seismicity), the design of pressurized shells can vary greatly. Most modern containments (about 95%) are shell structures of various sizes made of concrete , reinforced or prestressed , most often cylindrical in shape [4] [10] .
The hermetic jacket is a complex structure, which also includes systems of complex pipe and cable penetrations of large size. The containment is carried out by special technical supervision with regular tests of their functions and inspections of state bodies . Strict requirements are imposed on materials, installation, commissioning and operation [4] [11] .
The first pressurized shell in the world was built at Connecticut Yankee NPP ( USA ), which was commissioned in 1968 .
Reactor Type Differences
Water-Water Reactors
The main equipment of the reactor installation is located in the pressurized shells of water-water reactors : the reactor, primary loop circuits , main circulation pumps, steam generators , as well as the central hall, the spent fuel pool , the polar crane , some auxiliary systems and other equipment. Almost all used hermetic shells of the so-called “dry” type [12] [6] .
For pressurized water reactors, the main factor determining the importance of a pressurized shell is the need to absorb the load due to the increase in pressure associated with rupture of the primary circuit pipelines . A slight vacuum is always maintained in the container to mitigate the effects of the shock wave. The main auxiliary system is the sprinkler system , which provides spraying of cold water from the nozzles under the dome to condense the steam and thus reduce the pressure [9] [13] [14] .
Reinforced concrete and prestressed shells first appeared in the USA. The first, reinforced concrete, was built at the Connecticut Yankee Nuclear Power Plant , which was commissioned in 1968 . The prestress was first applied at the nuclear power plant Robert E. Jinn (launch in 1969 ), but only partial, vertical in the walls. Full prestressing of walls and domes was first applied at Palisades NPP (commissioning in 1971 ). Then, the practice of building pressurized concrete shells began to spread more and more widely in the USA, Canada, Japan, Belgium ( Tianzh NPP , block 1, 1975 ), France ( Fessenheim NPP , blocks 1-2, 1977 ), THE USSR. The first use of such a containment in Soviet reactor engineering was the Loviisa NPP with VVER-440 reactors in Finland (the first unit was launched in 1977 ), then, starting from the Novovoronezh NPP (unit 5, commissioning in 1980), units with VVER-1000 were built in the USSR equipped with pressurized shells [12] [15] .
The pressurized shells of water-water reactors are large: usually the volume is from 75,000 to 100,000 m³, in Soviet and Russian projects - from 65,000 to 67,000 m³. Such a large volume is necessary for the perception of energy released during an accident. In most cases, they are designed for an internal pressure of 0.5 M Pa . There are two approaches:
- single shell with inner metal cladding. The most common, used in most countries, including the United States, Japan, Russia. They are mainly cylindrical in shape; most German projects are characterized by a hemispherical steel shell.
- double, often with a large space between the shells, with or without internal metal cladding (the so-called “French” version). An external, non-stressed shell for protection against external influences and an internal, prestressed, for localizing accidents with depressurization of the primary circuit. In France, double shells are used for reactors with a capacity of 1300 MW or more, they are also used in the latest power units in Belgium [7] . The double-containment option was initially considered in the USSR for VVER-1000 reactors, however, by the decision of the chairman of the USSR State Committee for the Use of Atomic Energy Petrosyants , a single option was chosen [16] . In the 2000s, for a new project of NPP-2006 with VVER-1200 reactors, Russia decided to use a double containment with steel inner lining. The volume of the inner shell is 65,000 m³, between the inner and outer shells - a space with a volume of 18,000 m³ [17] .
Other species, except for “dry” containment tanks, have not been constructed for water-cooled reactors in recent decades. Previously, two more types were used in small quantities, which were smaller [12] :
- with an ice condenser within the containment, which is able to condense steam in the event of an accident (for example, the Sequoia and Watts Bar stations in the United States) [9] ;
- with a deep vacuum in the containment, to smooth out the sharp impact and partially compensate for the increasing pressure in the accident.
Typical Features
Geometry
Most often, pressurized shells have the shape of a cylinder with a hemispherical dome resting on a concrete base.
- inner diameter from 37 to 45 meters;
- wall and dome thickness from 0.8 to 1.3 meters;
- base thickness from 1 m (rock or support on a special structure, as in VVER-1000 reactors) to 5 m (insufficiently hard soil under the base, high seismicity, prestressed base);
- the total height of typical shells is 50-60 meters [18] .
Penetrations
The equipment inside the containment is connected with numerous auxiliary and emergency systems outside, so piping and cable entry is required through the walls, for which a system of pressurized pipe and cable penetrations of various sizes is provided in the containment. There are about 120 on average. The largest openings are: a transport hatch for loading / unloading equipment and fuel - a diameter of about 8 meters; main and emergency locks for the passage of personnel - 3 meters each; penetration of steam pipelines - 1.3 meters [18] .
Maximum design parameters for an accident
- pressure is most often 0.5 MPa;
- temperature is most often 150 ° C [18] .
Tension and Strength
On average, the stress of the cylindrical part of a typical prestressed container during normal operation is 10 MPa in the tangential direction and 7 MPa in the vertical direction, which provides reinforced concrete strength of about 40 MPa [18] .
Cladding
The inner lining, if any, is most often made of steel, with a thickness of 6 ... 8 mm. Cladding is required to improve sealing and greater resistance to stress [18] .
Consumption of materials
The indicated values vary greatly depending on the project.
Single cladding with cladding (for a power unit with a capacity of about 900 MW) [18] :
| Material | Containerization | Base | Total |
|---|---|---|---|
| Concrete , m³ | 8000 | 5000 | 13,000 |
| Armature , t | 1000 | 800 | 1800 |
| Prestressed steel , t | 1000 | - | 1000 |
| Steel cladding, t | 500 | 150 | 650 |
Double cladding without cladding (for a power unit with a capacity of about 1400 MW) [18] :
| Material | Inner shell | Outer shell | Base | Total |
|---|---|---|---|---|
| Concrete , m³ | 12 500 | 6000 | 8000 | 26,500 |
| Armature , t | 1150 | 850 | 1500 | 3500 |
| Prestressed steel , t | 1500 | - | - | 1500 |
Boiling Reactors
10 - concrete containment;
19 - steel shell;
24 - bubbler tank
Most boiling reactors operate in the United States, Japan ( General Electric and its licensees, Toshiba and Hitachi ), Sweden ( ABB ) and Germany ( Kraftwerk Union ).
All boiling reactors are designed with pressure reduction systems in the containment. Containment consists of two main parts - a dry shaft (dry box) of the reactor ( English dry-well ) and a bubbler tank ( English wet-well ). In the event of an accident with loss of coolant within the pressurized volume, the steam is sent using peaks (guiding devices) to the bubbler tank with water, where it condensates. In addition, there are also systems with spraying water in a pressurized volume. Due to this design, the volumes of the shells are quite small - about 1/6 of the size of the “dry” shell of water-cooled reactors. Almost all auxiliary systems are located in the building surrounding the containment. This building serves as the second containment ( Eng. Secondary containment ), it supports a weak rarefaction [19] [20] [21] .
Most of the first projects of General Electric and its licensees in various countries have concrete containers with a pear-shaped steel inner shell that separates the dry box from the bubbler tank. In Scandinavia, ABB units, for example, in Sweden and Finland ( Olkiluoto NPPs ), are equipped with pressurized shells made of prestressed concrete with steel cladding, which is covered in the upper part with a steel dome. The base and top are only partially prestressed. In Germany, Kraftwerk Union power units initially equipped with steel hemispherical pressurized shells, then design decisions changed to cylindrical shells of prestressed reinforced concrete with steel cladding and additional protection against aircraft crashing in the upper part (blocks B and C of Gundremmingen NPP ). In power units with improved boiling reactors , which are being built by General Electric and its licensees in Japan and Taiwan, the containment unit is integrated into the reactor compartment building in such a way that the overall size of the structure is reduced and seismic resistance is increased due to lowering the center of gravity [19] [20] [21 ] ] .
To solve the problem of hydrogen accumulation, which is much sharper in boiling reactors due to the smaller shell size, early construction of containers uses filling the dry shaft of the reactor with inert gas (for example, pure nitrogen ), in later projects hydrogen afterburning systems are provided [9] [ 22] .
Typical Features
Geometry
A typical shell is a cylinder (often with a spherical thickening in the lower part) mounted on a massive slab and topped with a slab of prestressed reinforced concrete with a removable metal cap for access to the reactor. The inner diameter is usually 26, the height is 35 meters, and for improved boiling reactors it is 3 meters larger at a 29.5-meter height [23] .
Penetrations
The number of holes is about 100, and there is no hole for the transport hatch (the largest hole in the shells of water-cooled reactors). Gateways for staff have a diameter of 2.5 meters [23] .
Maximum design parameters for an accident
The calculated parameters are, on average, slightly higher than that of the shells of pressurized water reactors: pressure — usually 0.6 MPa, temperature — 170 ° C [23] .
Cladding
The inner lining is made of steel with a thickness of 6 ... 10 mm [23] .
Heavy Water Reactors
Heavy water reactors are mostly known as CANDU , a Canadian national destination. Canada also built these reactors in South Korea, Pakistan, Romania, China and Argentina. Another state where reactors of this type are a national area is India. They were also built by the German Kraftwerk Union for example, at Atucha NPP in Argentina.
An example of standard CANDU pressure vessel design is the four power units of Pickering NPP . All of their cylindrical shells, in which the primary circuit equipment and steam generators are located, are connected to a separate special “vacuum” structure with a volume of 82,000 m³, in which a vacuum of 0.007 MPa is maintained. In the event of an accident with increasing pressure in the containment of one of the blocks, the membrane ruptures on the pipeline, and the emergency block is connected to the vacuum structure. Thus, the overpressure is completely relieved in less than 30 seconds, even in the event of failure of the emergency power unit systems. Both pressurized shells and the vacuum structure are equipped with sprinkler (spray) and ventilation systems to condense steam and reduce pressure. Also in the vacuum building there is an additional tank with an emergency supply of water for these purposes. The design pressure of the reactor shells is 0.42 MPa with a vacuum structure and 0.19 MPa without it. Pressure shells are made of prestressed concrete, the vacuum structure is made of reinforced concrete. The inner lining of the shells is made of rubber based on epoxy resins and vinyl , reinforced with fiberglass , a vacuum structure without cladding. In later projects, for example, the Canadian Bruce NPP , the shell lining is made of steel, and the reinforced concrete of the vacuum structure is prestressed [24] [25] [26] .
The containment shells of Indian reactors developed in a different direction. Unlike Canadian reactors, Indian shells are double, without an inner lining and with a bubbler tank in a pressurized volume. The container is divided by waterproof partitions into a dry box and bubbler tank. In the event of an accident, the steam-water mixture through the ventilation system is discharged from the dry box to the bubbler tank and condenses. Blocks of the Rajasthan NPP (start-up in 1981 ) were the first in India from prestressed concrete (only a dome, walls made of reinforced concrete). In a subsequent project, Madras NPP , the separation of volumes into a dry box and bubbler was applied. The pressurized shells of the power units of this station are partially double, the inner shell of prestressed, and the outer shell of monolithic, unreinforced concrete. The next stage of evolution was the containment of the Naror NPP , in which the outer shell is made of reinforced concrete. Then, at the Kakrapar NPP, the outer dome was removable for the possibility of replacing steam generators. This design, with minor modifications, has been used at many Indian power units [24] .
Other types
Fast neutron breeder reactors were developed and operated in several countries (USA, Japan, Great Britain, France, USSR), however, at the moment, there is only the only one in the world that operates at Beloyarsk NPP in Russia. Так как теплоносителем в таких реакторах является жидкий металл, а не вода, гермооболочки, бетонные или стальные, рассчитываются на значительно меньшее давление — 0,05—0,15 МПа [27] .
Газоохлаждаемые реакторы ( Magnox и AGR ) — национальное направление в реакторостроении Великобритании. Такие реакторы не имеют гермооболочек. Основное оборудование в них интегрировано с активной зоной в корпус из предварительно-напряжённого железобетона, который, таким образом, играет роль контейнмента [27] .
Высокотемпературные газоохлаждаемые реакторы строились в 60-е, и все были закрыты к концу 80-х годов. В США компанией General Atomics были построены несколько энергоблоков станций «Форт-Сент-Врейн» и «Пич-Боттом» . Гермооболочки цилиндрической формы из железобетона c куполом, внутри находятся реактор из предварительно-напряжённого железобетона и основное оборудование. Расчётное давление — 0,35 МПа. В Германии действовал реактор THTR-300 компании Nukem без гермооболочки, с цилиндрическим реактором из предварительно-напряжённого железобетона [27] .
В энергоблоках с реакторами РБМК , которые строились в СССР, гермооболочки не использовались из-за больших размеров реактора. Роль контейнмента выполняет система бетонных боксов вокруг реактора, в которых находится основное оборудование, и бассейн-барботёр для сброса пара в случае аварийной ситуации [27] [28] .
Современные тенденции
Современные тенденции в сооружении гермооболочек направлены, в основном, в сторону наращивания пассивных, то есть не требующих источников энергии и сигнала на включение систем. В этом направлении активно развивались все аварийные системы в реакторах последнего, 3+ поколения. В настоящее время ведётся строительство четырёх ВВЭР-1200 ( Нововоронежская АЭС-2 и Ленинградская АЭС-2 ) в России, четырёх AP1000 (компания Westinghouse ) в Китае и четырёх EPR ( Areva совместно с Siemens ) в Финляндии, Франции и Китае. Россия уже использовала новые решения при строительстве Тяньваньской АЭС в Китае и АЭС Куданкулам в Индии. Существует и целый ряд других проектов различных компаний мира, реализация которых ещё не начата.
Во всех новых проектах гермооболочки двойные, внешняя для защиты от внешних воздействий и внутренняя для локализации аварий с разгерметизацией первого контура. В ВВЭР-1200 и EPR внешняя оболочка из железобетона, внутренняя из предварительно-напряжённого железобетона. В AP1000 внутренняя оболочка стальная. Во всех проектах между внутренней и внешней оболочками в случае аварии организуется естественная циркуляция воздуха для охлаждения внутренней оболочки [13] [17] [29] [30] [31] .
Другим направлением в повышении безопасности является защита гермооболочки в случае расплавления ядерного топлива и прожигания им корпуса реактора. Впервые подобное устройство было сооружено в контейнменте Тяньваньской АЭС с ВВЭР-1000 (пуск в 2007 году ) и принято для проектов с ВВЭР-1200. В российских гермооболочках ловушка расплава сооружается под реактором, в её корпусе находится наполнитель, в основном из оксидов железа и алюминия [32] . Наполнитель растворяется в расплаве топлива для уменьшения его объёмного энерговыделения и увеличения поверхности теплообмена, а вода по специальным трубопроводам заливает эту массу [17] . В EPR ловушка организована по-другому — расплав, прожёгший корпус, попадает на наклонную поверхность, направляющую его стекание в бассейн с водой и охлаждаемым металлическим днищем специальной конструкции. В AP1000 ловушка расплава отсутствует, но предусмотрена система для предотвращения прожигания корпуса — шахта реактора в случае такой аварии заливается водой, охлаждающей корпус снаружи [30] [31] .
Известным нововведением в области пассивной безопасности являются каталитические рекомбинаторы водорода. Их можно устанавливать и на уже работающих блоках (на множестве АЭС по всему миру они уже установлены), в обязательный набор элементов они входят в новых проектах. Рекомбинаторы — небольшие устройства, которые во множестве устанавливаются по всему гермообъёму и обеспечивают снижение концентрации водорода при авариях с его выделением. Рекомбинаторы не требуют источников энергии и команд на включение — при достижении небольшой концентрации водорода (0,5—1,0 %) процесс его поглощения рекомбинаторами начинается самопроизвольно [30] [33] .
Notes
- ↑ Общие положения обеспечения безопасности атомных станций . Основные термины и определения
- ↑ 1 2 3 4 Защитная оболочка // Глоссарий Института проблем безопасного развития атомной энергетики РАН
- ↑ Глоссарий МАГАТЭ по вопросам безопасности
- ↑ 1 2 3 4 Nuclear containments: state-of-art report . — Stuttgart: Fédération internationale du béton , 2001. — P. 1. — 117 p. — ISBN 2-883-94-053-3 .
- ↑ Кайоль А., Щапю К., Щоссидон Ф., Кюра Б., Дюонг П., Пелль П., Рище Ф., Воронин Л. М., Засорин Р. Е., Иванов Е. С., Козенюк А. А., Куваев Ю. Н., Филимонцев Ю. Н. Безопасность атомных станций. — Paris: EDF -EPN-DSN, 1994. — С. 29—31. - 256 s. — ISBN 2-7240-0090-0 .
- ↑ 1 2 Paul Ih-fei Liu. Energy, technology, and the environment . — New York: ASME , 2005. — P. 165—166. — 275 p. — ISBN 0-7918-0222-1 .
- ↑ 1 2 Swarup R., Mishra SN, Jauhari VP Environmental Science And Technology . — New Delhi: Mittal publications, 1992. — P. 68—79. — 329 p. — ISBN 81-7099-367-9 .
- ↑ Самойлов О. Б., Усынин Г. Б., Бахметьев А. М. Безопасность ядерных энергетических установок. — М. : Энергоатомиздат , 1989. — С. 26—27. - 280 p. — ISBN 5-283-03802-5 .
- ↑ 1 2 3 4 Jan Beyea, Frank Von Hippel. Containment of a reactor meltdown (англ.) // Bulletin of the Atomic Scientists . - 1982. - Vol. 38 , no. 7 . — P. 52—59 . — ISSN 0096-3402 .
- ↑ Ray Nelson. Manufactured Meltdown (англ.) // Popular Science . — Bonnier Group , 1988. — Vol. 232 , no. 1 . — P. 66—67. — ISSN 0161-7370 .
- ↑ Nuclear powerplant standardization : light water reactors . — Washington: United States Government Printing Office , 1981. — P. 19—20. — 63 p.
- ↑ 1 2 3 Nuclear containments: state-of-art report . — Stuttgart: Fédération internationale du béton , 2001. — P. 9—11. — 117 p. — ISBN 2-883-94-053-3 .
- ↑ 1 2 Amano RS, Sunden B. Thermal Engineering in Power Systems . — Southampton: WIT Press , 2008. — P. 142—149. — 388 p. — ISBN 978-1-84564-062-0 .
- ↑ Anthony V. Nero, jr. A Guidebook to Nuclear Reactors . — Berkeley, Los Angeles, London: University of California Press , 1979. — P. 86—92. — 281 p. — ISBN 0-520-03482-1 .
- ↑ Андрюшин И. А., Чернышёв А. К., Юдин Ю. А. Укрощение ядра. Страницы истории ядерного оружия и ядерной инфраструктуры СССР . — Саров, 2003. — С. 354—356. — 481 с. — ISBN 5 7493 0621 6 . Архивировано 10 июля 2007 года. Архивная копия от 10 июля 2007 на Wayback Machine
- ↑ Charles K. Dodd. Industrial decision-making and high-risk technology: siting nuclear power facilities in the USSR . — Lanham, London: Rowman & Littlefield , 1994. — P. 87. — 212 p. — ISBN 0-8476-7847-4 .
- ↑ 1 2 3 Андрушечко С. А., Афоров А. М., Васильев Б. Ю., Генералов В. Н., Косоуров К. Б., Семченков Ю. М., Украинцев В. Ф. АЭС с реактором типа ВВЭР-1000. От физических основ эксплуатации до эволюции проекта . — М. : Логос, 2010. — 604 с. - 1000 copies. — ISBN 978-5-98704-496-4 .
- ↑ 1 2 3 4 5 6 7 Nuclear containments: state-of-art report . — Stuttgart: Fédération internationale du béton , 2001. — P. 19—22. — 117 p. — ISBN 2-883-94-053-3 .
- ↑ 1 2 Nuclear containments: state-of-art report . — Stuttgart: Fédération internationale du béton , 2001. — P. 12—15. — 117 p. — ISBN 2-883-94-053-3 .
- ↑ 1 2 M.Ragheb. Containment structures (англ.) (недоступная ссылка) . University of Illinois at Urbana–Champaign (16 March 2011). Дата обращения 21 марта 2011. Архивировано 15 мая 2011 года.
- ↑ 1 2 Anthony V. Nero, jr. A Guidebook to Nuclear Reactors . — Berkeley, Los Angeles, London: University of California Press , 1979. — P. 103—107. — 281 p. — ISBN 0-520-03482-1 .
- ↑ George A. Greene. Heat transfer in nuclear reactor safety . — San Diego: Academic Press , 1997. — P. 308. — 357 p. — ISBN 0-12-020029-5 .
- ↑ 1 2 3 4 Nuclear containments: state-of-art report . — Stuttgart: Fédération internationale du béton , 2001. — P. 24. — 117 p. — ISBN 2-883-94-053-3 .
- ↑ 1 2 Nuclear containments: state-of-art report . — Stuttgart: Fédération internationale du béton , 2001. — P. 16—17. — 117 p. — ISBN 2-883-94-053-3 .
- ↑ Anthony V. Nero, jr. A Guidebook to Nuclear Reactors . — Berkeley, Los Angeles, London: University of California Press , 1979. — P. 116. — 281 p. — ISBN 0-520-03482-1 .
- ↑ Canada enters the nuclear age: a technical history of Atomic Energy of Canada Limited as seen from its research laboratories . — Canada: AECL , 1997. — P. 314—318. — 439 p. — ISBN 0-7735-1601-8 .
- ↑ 1 2 3 4 Nuclear containments: state-of-art report . — Stuttgart: Fédération internationale du béton , 2001. — P. 18. — 117 p. — ISBN 2-883-94-053-3 .
- ↑ Доллежаль Н.А. , Емельянов И.Я. Канальный ядерный энергетический реактор. — М. : Атомиздат , 1980. — P. 153—169. — 208 p.
- ↑ Alan M. Herbst, George W. Hopley. Nuclear energy now: why the time has come for the world's most misunderstood energy source . — New Jersey: John Wiley & Sons , 2007. — P. 150—153. — 229 p. — ISBN 978-0-470-05136-8 .
- ↑ 1 2 3 Saito T., Yamashita J., Ishiwatari Y., Oka. Y. Advances in Light Water Reactor Technologies . — New York, Dordrecht, Heidelberg, London: Springer , 2011. — 295 p. — ISBN 978-1-4419-7100-5 .
- ↑ 1 2 AP1000 (англ.) . Westinghouse (16 March 2011). Дата обращения 22 марта 2011. Архивировано 1 февраля 2012 года.
- ↑ Гусаров В. В., Альмяшев В. И., Хабенский В. Б., Бешта С. В., Грановский В. С. Новый класс функциональных материалов для устройства локализации расплава активной зоны ядерного реактора // Российский химический журнал . — М. , 2005. — № 4 . — С. 17—28 .
- ↑ Келлер В. Д. Пассивные каталитические рекомбинаторы водорода для атомных электростанций // Теплоэнергетика . — М. : МАИК «Наука/Интерпериодика» , 2007. — № 3 . — С. 65—68 . — ISSN 0040-3636 .
Literature
- Nuclear containments: state-of-art report . — Stuttgart: Fédération internationale du béton , 2001. — 117 p. — ISBN 2-883-94-053-3 .
- Bangash, MYH Structures for Nuclear Facilities . — Heidelberg, Dordrecht, London, New York: Springer , 2011. — 457 p. — ISBN 978-3-642-12560-7 .