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To clarify exactly what materialise at the Fukushima atomic power plants in Japan following a massive 8.9 - order of magnitude earthquake on Friday ( March 11 ) , LiveScience and its sister web site Life ’s Little Mysteries consulted Temipote Taiwo , a nuclear railroad engineer and steer atomic systems analyst at Argonne National Laboratory , a U.S. Department of Energy enquiry installation near Chicago , Illinois .
Q : How might the failure of a atomic power plant ’s cool system result in a meltdown ?
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A : Nuclear reactor mogul is derived from the fission chain reaction . Once you turn off ( or ' scram ' ) the reactor , the atomic string reaction is no longer hap . This appear to have successfully come about in the Japanese plant . Once the reactor is buzz off , the reactor power fall off significantly . However , there are fission products that are organise as a byproduct of the fission chemical reaction that remain in the fuel . These nuclear fission products continue to undergo radioactive decomposition , which raise some heating system ( call decay heat ) in the fuel . This is ab initio about 6 - 8 % of the nuclear reactor power , but this concentrate oestrus must be removed however . These radioactive nuclear fission products are normally contain in the intact fuel elements and their heat generation decrease with time . However , if you do not keep cooling the fuel factor to remove the decline estrus ( by having cooling water ) , the fuel will inflame up and then could dissolve . When the fuel melts , the fission products can be released from the fuel into the reactor pressure vessel and then into the containment , if the coolant leaks from the reactor vessel . Q : What actually pass during a atomic nuclear meltdown ?
A : A nuclear reactor - core meltdown incriminate that the nuclear reactor - substance initially composed of solid nuclear fuel rods has become liquified because of overheat due to the deprivation of adequate cooling . Full meltdownis predate by a complete uncovering of the nuclear reactor - core resulting from dehydration of coolant . During the process of core melting , the fuel cladding ( tube-shaped structure ) , which contains the fuel and cater the first barrier to radioactive fission production button , overheats and oxidizes by interacting with cooling water , lead in hydrogen gas pedal production . The hydrogen under sealed conditions might take fire . At very in high spirits temperature , which develops from the deficiency of adequate cooling system , the facing could melt . In the case of full nuclear meltdown , the molten fuel would penetrate and/or interact with the molten cladding . The fuel and facing might also shape a liquified bulk of material . [ Infographic : What Is a Nuclear Meltdown?]Q : Can a nuclear meltdown be stopped or reversed ?
A : The simmering pee reactor like to the Japan reactors have pleonastic exigency kernel chill systems to keep the meat nuclear meltdown , including emergency diesel motor generators and batteries to furnish power to the pumps in the event of external power departure . In the Japan nuclear reactor , all outside power to the station was lost when the seawater swept away the power lines . The diesel engine generator also come out to have finish function due to the tsunami induced price , and the fill-in batteries were consumed after a few hours . This is the likely progression of the seeming partial kernel meltdown . Re - stabilizing core cooling with urine is the only way to terminate further core melting . If passable cooling is re - established at a partial core thawing State Department , the reactor damage and extra liberation of fuel radioactivity content to the environs could be limited . This is why the operators of the Japan reactors are making all effort to allow for piddle for cool down the nuclear reactor . Q : What is a fond nuclear meltdown ?
A : This is exchangeable to the nuclear meltdown case above , except that only a fond fraction of the core ( upper - part ) has become uncovered and mellow due to modified cooling . Its impact is likely less . Q : How is this upshot in Japan different from the Chernobyl stroke ?
A : The two events are different . First of all , the Japan reactors exclude - down and the power level was reduced immediately to the decomposition power level ( about 6 - 8 percent of the normal operating mogul ) when the earthquake first hit , whereas the Chernobyl reactor failed to close down and its magnate was increase , due to the progression of that accident . moreover , the reactors in Japan have a containment complex body part while the Chernobyl reactor did not have such a complex body part . This structure provides a worthful childbed of radiation in the outcome of gaseous discharge or reactor vas breach that would leave in the firing of radioactive cloth into the atmosphere , as happened in Chernobyl . So this capability is a tremendous advantage for a reactor design with containment . Additionally , there is no possibility of a graphite fervour in Japan , as in the Chernobyl case , since graphite is not a mental synthesis material in the Nipponese reactors .
Furthermore , the Chernobyl accident was due to an explosion inside the reactor itself , which distributed a meaning fraction of radioactive material up into the air where they formed a plumage that cover a large fraction of Europe . The dispersal was made bad by the lack of a containment structure . In the Japan case , radiation releases have resulted from slow degradation and loss of radioactive materials from the reactor fuel due to the want of cool . This lack of cooling is due to the combined personal effects of the earthquake and follow - on tsunami that have entirely wiped out electric power ( both normal and emergency brake backup diesel source ) for days at these works . This is call a station blackout . The electricity is needed to run weewee pump to cool the cores . Unlike the burst inside the core itself at Chernobyl , there have been some atomic number 1 explosions at the Japan plants , but these have been outside the containment and appear not have damaged the reactors or the reactor containment . Finally , there have been some controlled radiation outflow from the plant life in the form of radioactivity in steam that was vented to keep the containment from over - pressurizing , as opposed tothe uncontrolled release at Chernobyl . The amount of irradiation ( radiation ) release from the Japan plant is a very small fraction of that released from Chernobyl . Q : What ’s the regretful that could happen at one of the Japan nuclear facilities ?
A : The worst thing that could happen is that reactor containment could fail , lead to extra liberation of radioactivity into the environment . This could take place if they were not capable to cool the fuel and enough steam pressure is built - up in the containment to bust it . At this time the extent of the impact that this would have has diminished since many of the fission products have already undergone radioactive decay and so even if the containment did fail , there would be less of an impact on the surrounding area .
