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into the primary containment structure in other types of containments, such as large-dry or ice-condenser containments (typically used in pressurized water reactor designs). The actuation of these valves depressurizes the reactor vessel and allows lower pressure coolant injection systems to function, which have very large capacities in comparison to the high pressure systems. Some depressurization systems are automatic in function, while others may require operators to manually activate them. In pressurized water reactors with large dry or ice condenser containments, the valves of the system are called
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187:, in various alloys with structural backing such as steel. In addition to being neutron absorbent, the alloys used also are required to have at least a low coefficient of thermal expansion so that they do not jam under high temperatures, and they have to be self-lubricating metal on metal, because at the temperatures experienced by nuclear reactor cores oil lubrication would foul too quickly.
361:
battery power, emergency generator, or off-site electrical power. The
Isolation cooling system is a defensive system against a condition known as station blackout. This system is not part of the ECCS and does not have a low coolant accident function. For pressurized water reactors, this system acts in the secondary cooling circuit and is called
478:
system usually consists of a large metal and/or concrete structure (often cylindrical or bulb shaped) that contains the reactor vessel. In most reactors it also contains the radioactively contaminated systems. The primary containment system is designed to withstand strong internal pressures resulting
390:
Diesel generators are employed to power the site during emergency situations. They are usually sized such that a single one can provide all the required power for a facility to shut down during an emergency. Facilities have multiple generators for redundancy. Additionally, systems that are required
318:
The
Automatic Depressurization System (ADS) consists of a series of valves which open to vent steam several feet under the surface of a large pool of liquid water (known as the wetwell or torus) in pressure suppression type containments (typically used in boiling water reactor designs), or directly
351:
This system consists of a series of pumps and spargers that spray coolant into the upper portion of the primary containment structure. It is designed to condense the steam into liquid within the primary containment structure in order to prevent overpressure and overtemperature, which could lead to
333:
An LPCI is an emergency system which consists of a pump that injects a coolant into the reactor vessel once it has been depressurized. In some nuclear power plants an LPCI is a mode of operation of a residual heat removal system, also known as an RHR or RHS but is generally called LPCI. It is also
301:
The High
Pressure Coolant Injection (HPCI) System consists of a pump or pumps that have sufficient pressure to inject coolant into the reactor vessel while it is pressurized. It is designed to monitor the level of coolant in the reactor vessel and automatically inject coolant when the level drops
432:
is the first layer of protection around the nuclear fuel and is designed to protect the fuel from corrosion that would spread fuel material throughout the reactor coolant circuit. In most reactors it takes the form of a sealed metallic or ceramic layer. It also serves to trap fission products,
360:
This system is often driven by a steam turbine to provide enough water to safely cool the reactor if the reactor building is isolated from the control and turbine buildings. Steam turbine driven cooling pumps with pneumatic controls can run at mechanically controlled adjustable speeds, without
220:
also can SCRAM the reactor completely with the help of their control rods. PWRs also use boric acid to make fine adjustments to reactor power level, or reactivity, using their
Chemical and Volume Control System (CVCS). In the case of LOCA, PWRs have three sources of backup cooling water, high
253:
cooling ponds, the ESWS is a safety-critical system. Since the water is frequently drawn from an adjacent river, the sea, or other large body of water, the system can be fouled by seaweed, marine organisms, oil pollution, ice and debris. In locations without a large body of water in which to
566:
In case of a radioactive release, most plants have a system designed to remove radioactivity from the air to reduce the effects of the radioactivity release on the employees and public. This system usually consists of containment ventilation that removes radioactivity and steam from primary
557:
filter; an exhaust fan; and associated valves, ductwork, dampers, instrumentation and controls. The signals that trip the SGTS system are plant-specific; however, automatic trips are generally associated with the electric heaters and a high temperature condition in the charcoal filters.
499:
In case of a full melt-down, the fuel would most likely end up on the concrete floor of the primary containment building. Concrete can withstand a great deal of heat, so the thick flat concrete floor in the primary containment will often be sufficient protection against the so-called
342:
This system uses spargers (pipes fitted with an array of many small spray nozzles) within the reactor pressure vessel to spray water directly onto the fuel rods, suppressing the generation of steam. Reactor designs can include core spray in high-pressure and low-pressure modes.
373:
Under normal conditions, nuclear power plants receive power from generator. However, during an accident a plant may lose access to this power supply and thus may be required to generate its own power to supply its emergency systems. These electrical systems usually consist of
546:(SGTS) is part of the secondary containment system. The SGTS system filters and pumps air from secondary containment to the environment and maintains a negative pressure within the secondary containment to limit the release of radioactive material.
516:
and increasing its heat conductivity; the diluted metallic mass could then be cooled by water circulating in the floor. Today, all new
Russian-designed reactors are equipped with core-catchers in the bottom of the containment building.
244:
The essential service water system (ESWS) circulates the water that cools the plant's heat exchangers and other components before dissipating the heat into the environment. Because this includes cooling the systems that remove
206:(LOCA), the water-loss of the primary cooling system can be compensated with normal water pumped into the cooling circuit. On the other hand, the standby liquid control (SLC) system (SLCS) consists of a solution containing
403:
that can provide uninterrupted electrical power to equipment for a brief period. Often they are used to provide electrical power until the plant electrical supply can be switched to the batteries and/or diesel generators.
784:
465:
is the first layer of shielding around the nuclear fuel and usually is designed to trap most of the radiation released during a nuclear reaction. The reactor vessel is also designed to withstand high pressures.
449:. Cladding does not constitute shielding, and must be developed such that it absorbs as little radiation as possible. For this reason, materials such as magnesium and zirconium are used for their low
289:
Emergency core cooling systems (ECCS) are designed to safely shut down a nuclear reactor during accident conditions. The ECCS allows the plant to respond to a variety of accident conditions (e.g.
508:
plant didn't have a containment building, but the core was eventually stopped by the concrete foundation. Due to concerns that the core would melt its way through the concrete, a "
512:" was invented, and a mine was quickly dug under the plant with the intention to install such a device. The device contains a quantity of metal designed to melt, diluting the
293:) and additionally introduce redundancy so that the plant can be shut down even with one or more subsystem failures. In most plants, ECCS is composed of the following systems:
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803:
302:
below a threshold. This system is normally the first line of defense for a reactor since it can be used while the reactor vessel is still highly pressurized.
848:
412:
Batteries often form the final redundant backup electrical system and are also capable of providing sufficient electrical power to shut down a plant.
270:
49:
924:
American
National Standard, ANSI N18.2, "Nuclear Safety Criteria for the Design of Stationary Pressurized Water Reactor Plants," August 1973.
221:
pressure injection (HPI), low pressure injection (LPI), and core flood tanks (CFTs). They all use water with a high concentration of boron.
643:
96:
68:
399:
Loss of electrical power can occur suddenly and can damage or undermine equipment. To prevent damage, motor-generators can be tied to
391:
to shut down the reactor have separate electrical sources (often separate generators) so that they do not affect shutdown capability.
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Basaltic concrete, with a calcium carbonate content of approximately 4 weight percent was assumed for the lower drywell floor.
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Each SGTS train generally consists of a mist eliminator/roughing filter; an electric heater; a prefilter; two absolute (
696:"Optimum Boiling Water Reactor Fuel Design Strategies to Enhance Reactor Shutdown by the Standby Liquid Control System"
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are to shut down the reactor, maintain it in a shutdown condition and prevent the release of radioactive material.
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containment. Control room ventilation ensures that plant operators are protected. This system often consists of
527:
53:
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133:
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Some plants have a secondary containment system that encompasses the primary system. This is very common in
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20:
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Generic
Results and Conclusions of Re-evaluating the Flooding in French and German Nuclear Power Plants
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Containment systems are designed to prevent the release of radioactive material into the environment.
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The failure of half of the ESWS pumps was one of the factors that endangered safety in the
727:
Corcoran, W.R.; Finnicum, D.J.; Hubbard, F.R. III; Musick, C.R.; Walzer, P.F. (May 1980).
8:
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because most of the steam systems, including the turbine, contain radioactive materials.
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and rapidly floods the core in case of problems with the stopping of the chain reaction.
869:
568:
554:
281:
375:
180:
501:
927:
IEEE 279, "Criteria for
Protection Systems for Nuclear Power Generating Stations."
903:"Deterministic Evaluations 19E-1 RS-5146900 Rev. 0 Design Control Document/Tier 2"
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are a series of rods that can be quickly inserted into the reactor core to absorb
852:
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from the core. All nuclear plants have some form of reactor protection system.
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the reactor completely with the help of their control rods. In the case of a
152:, the source of heat is eliminated. Other systems can then be used to remove
531:
509:
250:
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and rapidly terminate the nuclear reaction. They are typically composed of
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is designed to immediately terminate the nuclear reaction. By breaking the
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Union of
Concerned Scientists, published October 2007, accessed 2011-03-23
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Carlton, James D.; Kane, Edward R.; Parece, Martin V. (15 November 1993).
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505:
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523:, SNR-300, SWR1000, ESBWR, and Atmea I reactors have core catchers.
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from a leak or intentional depressurization of the reactor vessel.
168:
829:
J. M. Mattéi, E. Vial, V. Rebour, H. Liemersdorf, M. Türschmann,
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238:
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Deciphering
Fukushima, published 2011-03-08, accessed 2012-05-08
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Pre-construction safety report - Sub-chapter 9.2 – Water Systems
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229:
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Nuclear Industry in Russia Sells Safety, Taught by Chernobyl
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AREVA NP / EDF, published 2009-06-29, accessed 2011-03-23
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concrete floor specifically designed to catch the core.
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701:. University of Florida. pp. 24–25. Archived from
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filters that remove radioactive isotopes from the air.
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The great lesson France has to learn from Fukushima
433:especially those that are gaseous at the reactor's
352:leakage, followed by involuntary depressurization.
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56:. Unsourced material may be challenged and removed.
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254:dissipate the heat, water is recirculated via a
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755:"Method and system for emergency core cooling"
866:"Insight to Fukushima engineering challenges"
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772:
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249:from both the primary system and the spent
729:"The operator's role and safety functions"
363:Turbine driven auxiliary feedwater system
265:, while a total loss occurred during the
191:Safety injection / standby liquid control
116:Learn how and when to remove this message
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19:For broader coverage of this topic, see
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601:World Association of Nuclear Operators
586:Nuclear accidents in the United States
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415:
297:High pressure coolant injection system
285:HPCI and LPCI as a part of active ECCS
263:1999 Blayais Nuclear Power Plant flood
833:, published 2001, accessed 2011-03-21
687:
661:
632:
329:Low pressure coolant injection system
581:Boiling water reactor safety systems
562:Ventilation and radiation protection
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54:adding citations to reliable sources
25:
334:not a stand-alone valve or system.
13:
693:
14:
962:
456:
306:Automatic depressurization system
16:Nuclear safety systems in the USA
644:"Nuclear reactor rod controller"
642:Jabsen, Felix S. (10 May 1967).
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423:
338:Core spray system (only in BWRs)
235:Philippsburg Nuclear Power Plant
128:The three primary objectives of
30:
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668:Fisher, John R. (8 July 1968).
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140:Reactor protection system (RPS)
65:"Nuclear reactor safety system"
41:needs additional citations for
951:Nuclear power plant components
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612:
277:Emergency core cooling systems
225:Essential service water system
130:nuclear reactor safety systems
1:
670:"Nuclear reactor control rod"
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134:Nuclear Regulatory Commission
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544:standby gas treatment system
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369:Emergency electrical systems
322:Pilot-operated relief valves
7:
946:Nuclear safety and security
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273:nuclear accidents in 2011.
21:Nuclear safety and security
10:
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620:"Glossary: Safety-related"
591:Nuclear safety in the U.S.
218:Pressurized water reactors
18:
395:Motor generator flywheels
146:reactor protection system
356:Isolation cooling system
347:Containment spray system
204:loss of coolant accident
132:as defined by the U.S.
941:Nuclear reactor safety
596:Passive nuclear safety
315:
286:
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196:Boiling water reactors
150:nuclear chain reaction
538:Standby gas treatment
530:has a thick layer of
483:Secondary containment
435:operating temperature
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233:Cooling tower at the
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510:core catching device
50:improve this article
831:Eurosafe Forum 2001
476:primary containment
470:Primary containment
416:Containment systems
870:World Nuclear News
851:2012-10-29 at the
825:2011-10-06 at the
806:2014-04-24 at the
787:2022-10-19 at the
569:activated charcoal
555:activated charcoal
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210:, which acts as a
386:Diesel generators
376:diesel generators
181:transition metals
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872:. March 18, 2011
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760:. pp. 1, 7
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708:on 4 July 2021
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553:) filters; an
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502:China Syndrome
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61:Find sources:
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39:This article
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874:. Retrieved
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762:. Retrieved
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736:. Retrieved
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710:. Retrieved
703:the original
694:Fensin, ML.
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314:Passive ECCS
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198:are able to
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165:Control rods
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160:Control rods
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106:January 2011
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48:Please help
43:verification
40:
734:. p. 5
675:. p. 7
649:. p. 3
267:Fukushima I
177:lanthanides
935:Categories
801:Got Water?
625:2011-03-20
607:References
437:, such as
247:decay heat
208:boric acid
154:decay heat
76:newspapers
919:Standards
876:March 19,
506:Chernobyl
408:Batteries
401:flywheels
380:batteries
173:actinides
849:Archived
823:Archived
804:Archived
785:Archived
575:See also
532:basaltic
504:. The
251:fuel rod
169:neutrons
439:krypton
239:Germany
90:scholar
764:4 June
738:4 June
712:4 June
679:4 June
653:4 June
514:corium
447:iodine
183:, and
92:
85:
78:
71:
63:
906:(PDF)
758:(PDF)
732:(PDF)
706:(PDF)
699:(PDF)
673:(PDF)
647:(PDF)
443:xenon
291:LOCAs
200:SCRAM
185:boron
97:JSTOR
83:books
878:2011
766:2019
740:2019
714:2019
681:2019
655:2019
551:HEPA
528:ABWR
526:The
489:BWRs
474:The
461:The
445:and
428:The
378:and
269:and
69:news
52:by
937::
908:.
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838:^
774:^
634:^
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