511:
deformation simultaneously. These mechanisms have been extensively studied by researchers using burst criterion models. In one study, researchers developed a burst criterion for
Zircaloy-4 fuel claddings and determined that the effect of the steam environment on failure of the claddings is negligible at low temperatures. However, as the burst temperature increases, rapid oxidation of Zircaloy-4 claddings occurs leading to a sharp decrease in its ductility. In fact, at higher temperatures the burst strain pretty much drops to zero signifying that the oxidized cladding becomes so brittle locally that it is predicted to fail without any further deformation or straining.
36:
880:
398:
The
Fukushima Daiichi nuclear disaster in 2011 occurred due to a loss-of-coolant accident. The circuits that provided electrical power to the coolant pumps failed causing a loss-of-core-cooling that was critical for the removal of residual decay heat which is produced even after active reactors are
510:
The residual decay heat causes rapid increase in temperature and internal pressure of the fuel cladding which leads to plastic deformation and subsequent bursting. During a loss-of-coolant accident, zirconium-based fuel claddings undergo high temperature oxidation, phase transformation, and creep
339:
A great deal of work goes into the prevention of a serious core event. If such an event were to occur, three different physical processes are expected to increase the time between the start of the accident and the time when a large release of radioactivity could occur. These three factors would
531:
AlC MAX phase using a hybrid arc/magnetron sputtering technique followed by an annealing treatment. They subsequently investigated the mechanical properties and oxidation resistance in pure steam conditions at 1000 °C, 1100 °C, and 1200 °C under different oxidation times. Results
187:
produced by a reactor shutdown from full power is initially equivalent to about 5 to 6% of the thermal rating of the reactor. If all of the independent cooling trains of the ECCS fail to operate as designed, this heat can increase the fuel temperature to the point of damaging the reactor.
420:
as the material for fuel rod claddings due to its corrosion-resistance and low neutron absorption cross-section. However, one major drawback of zirconium alloys is that, when overheated, they oxidize and produce a runaway exothermic reaction with water (steam) that leads to the production of
133:
622:
layer on the Cr-coating acted as an oxygen diffusion barrier that protected the Zr substrate from oxidation whereas the FeCrAl coating degraded due to inter-diffusion between the coating and the Zr substrate at high temperature thereby allowing Zr to still oxidize.
291:
Under operating conditions, 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). This is measured by the
613:
Another recent study evaluated Cr and FeCrAl coatings (deposited on
Zircaloy-4 using atmospheric plasma spraying technology) under simulated loss-of-coolant conditions. The Cr coating displayed superior oxidation resistance. The formation of a compact
383:, it will be a double barrier of channels and the pressure vessel) will depend on temperatures and boundary materials. Whether or not the fuel remains critical in the conditions inside the damaged core or beyond will play a significant role.
518:
O) before rupture. For rapid ruptures due to high heating rates and internal pressures, there is negligible oxidation. However, oxidation plays an important role in fracture for low heating rates and low initial internal pressures.
357:. After the water has boiled, then the time required for the fuel to reach its melting point will be dictated by the heat input due to decay of fission products, the heat capacity of the fuel and the melting point of the fuel.
242:
The fuel and reactor internals may melt; if the melted configuration remains critical, the molten mass will continue to generate heat, possibly melting its way down through the bottom of the reactor. Such an event is called a
255:(and below) – however, current understanding and experience of nuclear fission reactions suggests that the molten mass would become too disrupted to carry on heat generation before descending very far; for example, in the
540:
AlC over other coating materials are that it has excellent stability under neutron irradiation, a lower thermal expansion coefficient, better thermal shock resistance, and higher temperature oxidation resistance.
274:
reactor, which has two large masses of relatively cool, low-pressure water (first is the heavy-water moderator; second is the light-water-filled shield tank) that act as heat sinks. Another example is the
331:(such as a large thermal heat sink around the reactor core, passively-activated backup cooling/condensing systems, or a passively cooled containment structure) that mitigate the risk of further damage.
500:
536:
AlC caused in increase in hardness and elastic modulus compared to the bare substrate. Additionally, the high-temperature oxidation resistance was significantly improved. The benefits of Ti
399:
shut down and nuclear fission has ceased. The loss of reactor core cooling led to three nuclear meltdowns, three hydrogen explosions and the release of radioactive contamination.
140:
after a loss-of-coolant accident. After reaching an extremely high temperature, the nuclear fuel and accompanying cladding liquefies and relocates itself to the bottom of the
825:
Wang, Yiding; Zhou, Wancheng; Wen, Qinlong; Ruan, Xingcui; Luo, Fa; Bai, Guanghai; Qing, Yuchang; Zhu, Dongmei; Huang, Zhibin; Zhang, Yanwei; Liu, Tong (2018-06-25).
276:
259:
the reactor core melted and core material was found in the basement, too widely dispersed to carry on a chain reaction (but still dangerously radioactive).
402:
The hydrogen explosions can be directly attributed to the oxidation of zirconium by steam in the fuel claddings as a result of the loss-of-coolant.
527:
The zirconium alloy substrates can be coated to improve their oxidation resistance. In one study, researchers coated a Zirlo substrate with Ti
545:
provides a good indication of the improved mechanical properties as a result of the coating and improved resistance to plastic deformation.
652:
100:
900:
300:
have a negative void coefficient, indicating that as water turns to steam, power instantly decreases. Two exceptions are the Soviet
72:
53:
17:
79:
657:
827:"Behavior of plasma sprayed Cr coatings and FeCrAl coatings on Zr fuel cladding under loss-of-coolant accident conditions"
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351:(immediate and full insertion of all control rods), so reducing the thermal power input and further delaying the boiling.
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393:
119:
68:
905:
411:
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160:; if not managed effectively, the results of a LOCA could result in reactor core damage. Each nuclear plant's
57:
167:
Nuclear reactors generate heat internally; to remove this heat and convert it into useful electrical power, a
161:
380:
739:
Suman, Siddharth; Khan, Mohd. Kaleem; Pathak, Manabendra; Singh, R. N.; Chakravartty, J. K. (2016-10-01).
251:" would be this process taken to an extreme: the molten mass working its way down through the soil to the
721:. United States Patent and Trademark Office, Federal Government of the United States, Washington, DC, USA
216:
780:"A high oxidation resistance Ti2AlC coating on Zirlo substrates for loss-of-coolant accident conditions"
870:
662:
93:
884:
826:
779:
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693:"DOE fundamentals handbook - Decay heat, Nuclear physics and reactor theory, vol. 2, module 4, p. 61"
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212:
502:. Such reactions are what led to the hydrogen explosions in the Fukushima Daiichi nuclear disaster.
363:. The time required for the molten metal of the core to breach the primary pressure boundary (in
283:
fuel halts the fission reaction by removing the hydrogen moderator. The same principle is used in
270:, for instance, can withstand extreme temperature transients in its fuel. Another example is the
248:
141:
46:
328:
263:
514:
The amount of oxygen picked up by the zirconium alloy depends on the exposure time to steam (H
778:
Li, Wentao; Wang, Zhenyu; Shuai, Jintao; Xu, Beibei; Wang, Aiying; Ke, Peiling (2019-08-01).
340:
provide additional time to the plant operators in order to mitigate the result of the event:
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171:
system is used. If this coolant flow is reduced, or lost altogether, the nuclear reactor's
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364:
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Modern reactors are designed to prevent and withstand loss of coolant, regardless of their
8:
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137:
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323:, passively slow down the chain reaction when coolant is lost; others have extensive
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features that prevent meltdowns from occurring in these extreme circumstances. The
842:
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312:, on the other hand, are designed to have steam voids inside the reactor vessel.
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If water is present, it may boil, bursting out of its pipes. For this reason,
183:, the nuclear fuel will continue to generate a significant amount of heat. The
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The time required for the molten fuel to breach the primary pressure boundary
305:
741:"Rupture behaviour of nuclear fuel cladding during loss-of-coolant accident"
347:. Assuming that at the moment that the accident occurs the reactor will be
197:
632:
252:
208:
184:
715:"Patent Application 11/804450: Self-regulating nuclear power module"
35:
204:
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The time required for the water to boil away (coolant, moderator)
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Table 1. Mechanical properties of substrate and coated material
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to rapidly shut down the chain reaction, and may have extensive
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348:
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reactors this is the array of pressurized fuel channels; in
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Nuclear fuel § Common physical forms of nuclear fuel
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and weapons-production reactors, which use graphite as a
277:
Hydrogen
Moderated Self-regulating Nuclear Power Module
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60:. Unsourced material may be challenged and removed.
495:{\displaystyle {\ce {Zr + 2H2O -> ZrO2 + 2H2}}}
494:
247:and can have severe consequences. The so-called "
892:
522:
164:(ECCS) exists specifically to deal with a LOCA.
824:
706:
532:showed that coating the Zirlo substrate with Ti
319:, using various techniques. Some, such as the
777:
279:, in which the chemical decomposition of the
719:United States Patent Application Publication
207:and air are present, the graphite may catch
653:Nuclear fuel response to reactor accidents
136:A simulated animation of a core melt in a
477:
438:
120:Learn how and when to remove this message
712:
131:
14:
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658:Nuclear accidents in the United States
355:The time required for the fuel to melt
200:and backup supplies of cooling water.
196:are equipped with pressure-operated
58:adding citations to reliable sources
29:
505:
24:
394:Fukushima Daiichi nuclear disaster
388:Fukushima Daiichi nuclear disaster
25:
917:
405:
335:Progression after loss-of-coolant
215:. This situation exists only in
179:chain reaction. However, due to
901:Civilian nuclear power accidents
878:
713:Peterson, Otis G. (2008-03-20).
367:this is the pressure vessel; in
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27:Form of nuclear reactor failure.
831:Surface and Coatings Technology
757:10.1016/j.nucengdes.2016.07.022
45:needs additional citations for
843:10.1016/j.surfcoat.2018.03.016
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796:10.1016/j.ceramint.2019.04.089
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745:Nuclear Engineering and Design
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523:Oxidation Resistance Coatings
162:emergency core cooling system
156:) is a mode of failure for a
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663:Nuclear safety in the U.S.
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262:Some reactor designs have
69:"Loss-of-coolant accident"
648:Pressurized water reactor
213:radioactive contamination
173:emergency shutdown system
294:coolant void coefficient
175:is designed to stop the
150:loss-of-coolant accident
18:Loss of coolant accident
142:reactor pressure vessel
906:Nuclear reactor safety
784:Ceramics International
559:Elastic Modulus (GPa)
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329:passive safety systems
310:Boiling water reactors
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410:Further information:
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638:Containment building
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416:Most reactors use a
365:light water reactors
298:nuclear power plants
194:nuclear power plants
54:improve this article
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885:Nuclear technology
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268:Pebble Bed Reactor
257:Chernobyl disaster
233:Chernobyl disaster
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296:. Most modern
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392:Main article:
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379:reactors like
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325:safety systems
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264:passive safety
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65:Find sources:
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43:This article
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723:. Retrieved
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211:, spreading
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52:Please help
47:verification
44:
837:: 141–148.
751:: 319–327.
633:LOFT (LOCA)
575:5.39 ± 0.1
253:water table
895:Categories
725:2009-09-05
679:References
601:230.8±3.1
598:14.24±0.1
565:H/E (GPa)
421:hydrogen:
185:decay heat
80:newspapers
859:139798895
851:0257-8972
812:149686337
804:0272-8842
765:0029-5493
571:Substrate
456:⟶
698:20 April
627:See also
381:Atucha I
205:graphite
543:Table 1
349:SCRAMed
177:fission
169:coolant
94:scholar
871:Portal
857:
849:
810:
802:
763:
225:Magnox
96:
89:
82:
75:
67:
855:S2CID
808:S2CID
607:0.05
604:0.06
584:0.01
581:0.04
369:CANDU
306:CANDU
285:TRIGA
272:CANDU
231:(see
221:RBMKs
101:JSTOR
87:books
847:ISSN
800:ISSN
761:ISSN
700:2016
562:H/E
377:PHWR
373:RBMK
371:and
302:RBMK
235:and
217:AGRs
209:fire
154:LOCA
73:news
839:doi
835:344
792:doi
753:doi
749:307
460:ZrO
308:.
203:If
56:by
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590:Ti
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