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Topic: Loss of coolant accident

 Loss of coolant - Wikipedia, the free encyclopedia
A Loss of Coolant Accident (LOCA) is a mode of failure for a nuclear reactor; in a nuclear reactor, the results of a LOCA could be catastrophic to the reactor, the facility that houses it, and the immediate vicinity around the reactor.
A reactor may passively (that is, in the absence of any control systems) increase or decrease its power output in the event of a LOCA or of voids appearing in its coolant system (by water boiling, for example).
Some, such as the pebble bed reactor, passively shut down the chain reaction when coolant is lost; others have extensive safety systems to shut down the chain reaction.
www.wikipedia.org /wiki/Loss_of_coolant   (397 words)

 Patent 4362693: System for mitigating consequences of loss of coolant accident at nuclear power station
The most serious accident that may occur at a nuclear power station is a loss of coolant accident which means an instantaneous rupture of a pipeline of a maximum diameter and free escape of the coolant at both ends of that pipeline.
A loss of coolant accident normally results in a release of a large amount of steam, so a containment must be large and sturdy in order to withstand the pressure of the high-temperature steam-and-air mixture.
The reactor plant and coolant circuit equipment are arranged in the first compartment; the second compartment is intended to receive air driven from the first compartment by high pressure due to the release of steam after a loss of coolant accident.
www.freepatentsonline.com /4362693.html   (5427 words)

 Patent 4716011: BWR fuel assembly bottom nozzle with one-way coolant flow valve
Coolant in each fuel assembly then reverses its upward flow direction and exits downward through the inlet of the fuel assembly bottom nozzle into the lower plenum of the core and then out of the primary circuit.
Coolant flow through the openings 52 serves to equalize the hydraulic pressure between the four separate compartments 30, thereby minimizing the possibility of thermal hydrodynamic instability between the separate fuel rod subassemblies 46.
The coolant flow check valve 54 is operable to sense the direction of coolant flow through the inlet 58 and automatically, by action of the fluid on the valve, open when the flow direction sensed is into the bottom nozzle 16 (in the direction of arrow A in FIG.
www.freepatentsonline.com /4716011.html   (3148 words)

 Nat' Academies Press, Accident Precursor Analysis and Management: Reducing Technological Risk Through Diligence (2004)
Accident Precursor Analysis and Management: Reducing Technological Risk Through Diligence cantly influenced the way analyses are done, the nature of the results, and the types of insights expected from the program.
Accident Precursor Analysis and Management: Reducing Technological Risk Through Diligence The 1992 and 1993 precursor analyses included the potential use of alternate equipment and procedures, beyond those considered in the basic risk models, which had recently been added by licensees to provide additional protection against core damage.
Accident Precursor Analysis and Management: Reducing Technological Risk Through Diligence One of the major changes to the precursor selection process was a revision to the LER rule that became effective in 1984 requiring that a detailed report be provided of all operational events involving a reactor trip.
books.nap.edu /openbook/0309092167/html/89.html   (4623 words)

 Nat' Academies Press, Accident Precursor Analysis and Management: Reducing Technological Risk Through Diligence (2004)
Accident Precursor Analysis and Management: Reducing Technological Risk Through Diligence An example of this was the loss of some of the crew of the USS Squalus (SS-192), which was a precursor to the loss of the entire crew of the USS Thresher (SSN-593).
Accidents that are narrowly averted (near misses as described by Equation 5) should be examined as precursors, focusing on the factors that kept the consequences from being worse.
For example, the 2002 Davis-Besse situation did not become a loss-of-coolant accident because degradation of the reactor vessel head was discovered during repair of a crack in the nozzle.
books.nap.edu /openbook/0309092167/html/79.html   (3583 words)

 Nuclear submarine accidents
Nuclear accidents are classified either as "loss of control" (loss of regulation) accidents in which an uncontrolled chain reaction may occur, or as "loss of coolant accidents".
Due to the loss of coolant, the temperature in the reactor increased and the alarm went.
The incident was caused by a loss of coolant to the reactor, and is classified accordingly.
www.bellona.no /imaker?sub=1&id=11084   (5881 words)

Release categories characterize major classes of accident sequences in terms of the nature, timing, and magnitude of the release of radioactive material from the plant during a severe core damage accident.
Severe accidents are those that result in catastrophic fuel rod failure, core degradation and fission product release into the reactor vessel, containment or the environment.
The radiological source term for a given accident sequence or release category consists of the release fractions for various radionuclide groups (expressed as fractions of initial core inventory), and the timing, elevation, and energy of the release.
www.nuce.boun.edu.tr /psa/psaglossary.html   (1769 words)

One type of LOCA in which the ECCS would not prevent a meltdown is a large crack in the bottom of the reactor vessel, since water injected by the ECCS would simply pour out through that crack.
A person's risk of being a victim of such an accident is 20,000 times less than the risk of being killed by lightning, and 1,000 times less than the risk of death from an airplane crashing into his or her house.
Loss of lube oil is therefore not ordinarily considered to be a safety problem.
www.phyast.pitt.edu /~blc/book/chapter6.html   (12875 words)

 Online Ethics Center: Three Mile Island: Detailed Description of Accident   (Site not responding. Last check: 2007-10-15)
The accident at TMI could have been contained had either the PORV shut at this point, or the operators noticed that the valve was stuck open.
One of the factors which added to the severity of the accident at TMI was the inadequate training of the employees at the facility.
Following the accident, numerous tests were conducted in attempts to conclude what if any effect increased radiation would have on the health of human, animal and plant life in the surrounding area.
www.onlineethics.com /cases/tmi/desc.html   (2409 words)

To the surprise of the investigators, the high steam pressure that was created in the vessel by the loss of coolant blocked the flow of water from the ECCS.
Probably the most interesting finding from the LOFT large break LOCA test was the assessment of the conservatisms of the "Evaluation Model" used for nuclear power plant safety analysis calculations of large break LOCAs.
While no lives were lost and relatively little radiation released offsite, the accident resulted in a total loss of the three month old plant; thus, costing the utility billions in its investment, cleanup and, eventually, the complete decontamination and decommissioning.
users.owt.com /smsrpm/nksafe/seventies.html   (3282 words)

 Prologue   (Site not responding. Last check: 2007-10-15)
The accident focused national and international attention on the nuclear facility at Three Mile Island and raised it to a place of prominence in the minds of hundreds of millions.
In an accident, steam formation itself is not a danger, because it too can help cool the fuel rods, although not as effectively as the coolant water.
For example, in a loss-of-coolant accident (LOCA) -- that is, an accident in which there is a loss of the reactor's cooling water -- the Emergency Core Cooling System (ECCS) automatically uses existing plant equipment to ensure that cooling water covers the core.
stellar-one.com /nuclear/prologue.htm   (2272 words)

 TMI 25 Years Later: The Three Mile Island Nuclear Power Plant Accident and Its Impact   (Site not responding. Last check: 2007-10-15)
The dramatic accident held the world’s attention for an unsettling week in March 1979 as engineers struggled to understand what had happened and to bring the damaged reactor to a safe condition.
After the accident and the cleanup, a significant collection of videotapes, photographs, and reports were donated to the University Libraries at Penn State University.
In order to properly understand exactly what caused the accident and what it's effects meant to the local population, a rudimentary understanding of nuclear processes and power generation are needed.
www.enotalone.com /books/027102383X.html   (1099 words)

 Encyclopedia: Loss of coolant
In nuclear engineering, the void coefficient (more properly called void coefficient of reactivity) is a number that can be used to estimate how much the thermal output of a nuclear reactor increases (or decreases, if negative) as voids (steam bubbles) form in the reactor moderator or coolant.
Nuclear power currently involves converting the nuclear energy of fissable uranium into thermal energy by fission, from thermal to kinetic energy by means of a steam turbine and finally to electron energy by a generator.
A pressurized water reactor (PWR) is a type of nuclear power reactor that uses ordinary light water for both coolant and for neutron moderator.
www.nationmaster.com /encyclopedia/Loss-of-coolant   (731 words)

 Transient & Accident Safety Analysis   (Site not responding. Last check: 2007-10-15)
Every year the licensee also must submit to the NRC an update of all facility changes performed within the year for which NRC approval was not needed.
The reason these studies are done each cycle is that the fuel characteristics may change; thus the different types of accidents and transients could affect the fuel differently.
Some of the typical transients and accidents analyzed are reported in Section 14 of the Nuclear Power Plants' Final and Updated Safety Analysis Reports.
www.nucleartourist.com /operation/analysis.htm   (143 words)

 [No title]   (Site not responding. Last check: 2007-10-15)
At the moment of the accident, the reactor was running at the normal thermal output of 2440MW.
If the secondary coolant is lost or fails to run adequately, then the SG loses its heat-transfer function, causing the primary coolant overheated and the reactor core melt down.
The utility is yet to disclose specific information concerning the impact at the moment of the accident of the loss of that much amount of coolant water to the reactor's major cooling system, the steam-generator (SG).
www2.odn.ne.jp /~hal19090/Mihama-3.htm   (1417 words)

 EPA: Federal Register: Notice of Opportunity To Comment on Model Safety Evaluation on Technical Specification ...
Following an assumed loss of power to the RCP motor, the flywheel, in conjunction with the impeller and motor assembly, provides sufficient rotational inertia to assure adequate primary coolant flow during RCP coastdown, thus resulting in adequate core cooling.
The inspections are defined as in-place ultrasonic examination over the volume from the inner bore of the flywheel to the circle of one-half the outer radius or an alternative surface examination (magnetic particle testing [MT] and/or liquid penetrant testing [PT]) of exposed surfaces defined by the volume of the disassembled flywheel.
In conclusion, the staff finds that the regulatory positions in RG 1.14 concerning the three critical speeds are satisfied, and that the evaluation indicating that critical crack sizes are not expected to be attained during a 20-year inspection interval is reasonable and acceptable.
www.epa.gov /fedrgstr/EPA-IMPACT/2003/June/Day-24/i15860.htm   (2542 words)

 Cancer legacy of nuclear accident
A 1990 study had concluded that certain cancers were occurring among nearby residents at unusually high rates, but that radiation released during the accident was probably not the cause.
Whether radiation released during the accident caused these cancers, or whether the plant caused them in some other way is an interesting sidelight, but is not the central issue.
Shortly after the initial accident, government and industry officials got caught telling the public a series of bald-faced lies, compounding the public's initial distress.
www.greenleft.org.au /back/1997/273/273p15b.htm   (725 words)

 ANSWERS - CANSWEL2 - Modelling deformation of Zircaloy cladding under loss-of-coolant accident conditions   (Site not responding. Last check: 2007-10-15)
CANSWEL2 was developed to calculate the deformation of Zircaloy cladding (clad ballooning) under postulated loss-of-coolant accident conditions (LOCA) in water reactors.
Following initial application to SGHWR and Sizewell-B safety studies, it is continually being maintained to support current reactor safety analysis and design/interpretation of experimental facilities and their data over a wide range of conditions.
Assessment of the effect of choice of cladding materials on the LOCA safety case for reload fuel for Sizewell B. CANSWEL2 is available under licence from Serco Assurance as part of The ANSWERS Software Service set of codes, under which framework the code is maintained, supported and developed.
www.sercoassurance.com /answers/resource/areas/software/canswell2.htm   (675 words)

 Integrated Test of Severe Accident Analysis Code SAMPSON for the IMPACT Project
A 10-inch cold leg failure Loss of Coolant Accident in the Surry Plant was the assumed initiating event.
Because it is difficult to clarify various phenomena in the full-range of an accident scenario by experiments that pinpoint the significant events and investigate the specific phenomena in detail, analysis must be relied upon for understanding the entire scope of a severe accident.
The reactor coolant system is a three-loop design, with a reactor coolant pump and U-tube steam generator in each loop.
www.nupec.or.jp /database/paper/paper_12/p12_analysis2/R12-02-03.htm   (4799 words)

 Effect of PLUS7 Debris Filtering Capability on the Long Term Cooling After a Loss of Coolant Accident   (Site not responding. Last check: 2007-10-15)
During LTC after a LOCA, the ECC water to the safety injection pump is supplied from the containment sump and the debris smaller than the sump screen dimension are transported to the core so that the flow path at the core entrance region may be blocked by them.
The objective of LTC analysis is to confirm whether the reduced core flow rate by the blockage maintains the core at safe temperature levels while avoiding the precipitation of boric acid in the core region.
In conclusion, the PLUS7 debris filtering design, even it reduces the inlet flow rate to the core by the blockage due to the filtered debris, provides the satisfactory LTC capability, that is, the enough core cooling to remove the decay heat and the sufficient core flushing flow rate to avoid the precipitation of boric acid.
www3.inspi.ufl.edu /icapp03/program/abstracts/3128.html   (440 words)

 FEDSM99-7000: Uncertainty Analysis of Small-Break Loss-of-Coolant Accident in Pressurized Water Reactors   (Site not responding. Last check: 2007-10-15)
The purpose of the study was perform to the uncertainty analysis using the CSAU method.
In addition to the description of the uncertainty results, the process of phenomena identification in a two loop pressurized water reactor during small break loss of coolant accident and assessment the RELAP5/MOD3.2 code using the BETHSY facility, are described.
Uncertainty analysis was performed for SB LOCA with break in the cold leg using a new developed tool for response surface generation called optimal statistical estimator.
asme.pinetec.com /fedsm1999/data/s-289/7000.html   (224 words)

A loss of coolant accident could have occurred resulting in reactor coolant blowing out of the ruptured pipe and exploding into steam.
The Company said the accident was discovered on 10/1/1975, when 13 tonnes of radioactive water leaked from a crack in a pipe.
When the accident was reported gas was still leaking, forcing the evacuation of residents of Udall Rock.
prop1.org /2000/accident/facts4.htm   (7816 words)

 Les possibilités d'accident à un CANDU
Il va de soi qu'un accident nucléaire majeur occasionnerait une surchauffe excessive et, par conséquent, la fusion du combustible nucléaire.
Or, comme les accidents graves résultent d'un mélange de défaillances techniques et d'erreurs humaines, il n'est guère facile d'en prévoir les probabilités.
Le pire accident que l'on puisse imaginer verrait la dispersion de poisons radioactifs sur de grandes régions, tuant des milliers de personnes sur le coup, en tuant d'autres par l'augmentation de la susceptibilité au cancer, et provoquant des malformations génétiques qui affecteront les générations futures.
www.ccnr.org /CANDU_Safety_f.html   (3175 words)

 PSFC/JA-01-22 Abstract   (Site not responding. Last check: 2007-10-15)
Temperature Transients of Fusion-fission Hybrid Reactors in Loss of Coolant Accidents
Results show that for fission power densities of 5 to 10 MW/m3, none of the realistic variants investigated are completely passively safe; the critical time, defined as the time when either any structural part of the fusion-fission tokamak reaches melting point, or when the pebble fuel reaches 1873K, ranges from 5.5 to 80 hours.
Additionally, it is illustrated that, fundamentally, the LOCA characteristics of pure fission pebble beds and fusion-fission pebble beds are different.
www.psfc.mit.edu /library/01JA/01JA022/01JA022_abs.html   (266 words)

 WISE NC: NEW GENERATIONS: THE AP600   (Site not responding. Last check: 2007-10-15)
New in the design are the emergency core cooling systems designs, to prevent the overheating and melting of the reactor core in case of a Loss Of Coolant Accident (LOCA).
After an accident it is important to keep the containment intact.
The construction with a single containment would not provide protection to possible accidents from outside like an airplane crash, an explosion, etc. A double containment would affect the possibility to cool the containment by outside air.
www.antenna.nl /wise/492/4881.html   (1243 words)

 S/R 10: Three Mile Island: Then, Now and Next Time
Reactor coolant water, by now equivalent to reprocessing grade, was dumped into the river; and that radioactivity escaped into the atmosphere.
Burps and puffs of radioactive gases and particulate continued to leak throughout the cleanup of the accident.
The staff lied about the severity of the accident and to the Commissioners about the "falsification of leak rates" (the rate coolant water was leaking from the reactor—which was a federal criminal offense and for which Met-Ed was found guilty).
www.greens.org /s-r/10/10-05.html   (3377 words)

 Technical Glossary   (Site not responding. Last check: 2007-10-15)
A loss or discharge which occurs when two electrodes having a great difference of pressure are placed near together.
The maximum deviation (in degrees or percent) of a thermocouple or thermocouple extension wire from standard emf-temperature to be measured.
Abbreviation for Loss Of Coolant Accident, a system malfunction associated with nuclear generation stations.
www.coasteltools.com /glossary/glossary.htm   (6618 words)

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