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The containment building itself is typically an airtight steel structure enclosing the reactor normally sealed off from the outside atmosphere. The steel is either free-standing or attached to the concrete missile shield. In the United States , the design and thickness of the containment and the missile shield are governed by federal regulations (10 CFR 50.55a) {Link without Title} . TYPES Containment systems for nuclear power reactors are distinguished by size, shape, materials used, and suppression systems. The kind of containment used is determined by the type of reactor, generation of the reactor, and the specific plant needs. Suppression systems are critical to safety analysis and greatly affect the size of containment. Suppression refers to condensing the steam after a major break has released it from the cooling system. Due to the fact that decay heat doesn't go away quickly, there must be some ultimate method of suppression, but this may simply be heat exchange with the ambient air on the surface of containment. There are several common designs, but for safety-analysis purposes containments are categorized as either "large-dry," "sub-atmospheric," or "ice-condenser." Pressurized Water Reactors For a Pressurized Water Reactor , the containment also encloses the Steam Generator s and the pressurizer, and is the entire reactor building. The missile shield around it is typically a tall cylindrical or domed building. Early designs including Siemens, Westinghouse, and Combustion Engineering had a mostly can-like shape built with reinforced concrete. As concrete has a very good compression strength compared to tensile, this is a logical design for the building materials since the extremely heavy top part of containment exerts a large downward force that prevents some tensile stress if containment pressure were to suddenly go up. As reactor designs have evolved, many nearly spherical containment designs for PWRs have also been constructed. Depending on the material used, this is the most apparently logical design because a sphere is the best structure for simply containing a large pressure. Most current PWR designs involve some combination of the two, with a cylindrical lower part and a half-spherical top. Modern designs have also shifted more towards using steel containment structures. In some cases steel is used to line the inside of the concrete, which contributes strength from both materials in the hypothetical case that containment becomes highly pressurized. Yet other newer designs call for both a steel and concrete containment, notably the AP1000 and the European Pressurized Reactor plan to use both, which gives missile protection by the outer concrete and pressurizing ability by the inner steel structure. The AP1000 has planned vents at the bottom of the concrete structure surrounding the steel structure under the logic that it would help move air over the steel structure and cool containment in the event of a major accident (in a similar way to how a Cooling Tower works). |
Image:Brunswick NPPjpgA Typical Two-unit BWR At The
| "http://wwwinformationdelightinfo/information/entry/Brunswick_Nuclear_Generating_Station" class="copylinks">Brunswick Nuclear Generating Station |
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Image:CANDU At QinshanjpgThe
| "http://wwwinformationdelightinfo/information/entry/Qinshan_Nuclear_Power_Plant" class="copylinks">Qinshan Nuclear Power Plant is two-unit site where where the containment system is autonomous for each unit |
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Image:Pickering NPPjpgA Single Unit Of The
| "http://wwwinformationdelightinfo/information/entry/Pickering_Nuclear_Generating_Station" class="copylinks">Pickering Nuclear Generating Station , showing a slightly different shape from a typical PWR containment, which is mostly due to the larger footprint required by the Candu design |
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