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1、HowIsJapan'sNuclearDisasterDifferent?王小亮學(xué)號(hào):1090230113班級(jí):0902301Abstract:TherearesomekeydifferencesthatsetthecurrentFukushimasituationapartfromthe1979ThreeMileIslandemergencyandthe1986Chernobylnucleardisaster.Intermsofreactortype,Japan'sFukushimaDaiichinuclearpowercomplexismadeupofsixboiling
2、-waterreactors,orBWRs—atypeof"LightWaterReactor."WhereastheThreeMileIslandusedanothertypeofLightWaterReactorknownasapressurized-waterreactor,orPWR.InaPWR,thewateriskeptunderpressure.Thismeansthetemperaturecanbehigherthantheboilingpointofwaterwithoutgeneratingasignificantamountsteam(alesseff
3、icientcoolant).Sothereactorcoreoperatesatahighertemperatureinthesesystems,andheatcanbetransferredmoreefficiently.Boiling-waterreactorsoperateatlowertemperatures,andtheytendtobesimpler,withfewerparts.Chernobyl'sreactorswereatypecalledRBMK,whichalsousedwaterforthecoolant.ButunliketheLightWate
4、rReactors,theRMBKusedgraphiteasamoderator.Asamatteroffact,BWRorPWRtechnologiesareequallysafe.Bothtypesofreactorshaveakindofself-regulationor"negativefeedback"loop:Asthereactorgetshotter,thefissionreactionslowsdown,decreasingpower.TheRMBKdesign,ontheotherhand,"couldgointopositivefeedback,"wh
5、erehighertemperaturebegetsmorepower,whichinturnincreasesthetemperature,andsoon.Intheaspectofaccidentcauses,thetsunamiappearstobetheimmediateculpritintheFukushimadisaster,sincetheplantsshutdownastheyweredesignedtodofollowingtheearthquake.Whilethe"operatorerror"wasthefundamentalcauseoftheThre
6、eMileIslanddisasteraccident,becauseemergencycoolingsystemswereshutdown,withdirectconsequences.AttheChernobylreactorinUkraine,an"ill-conceived,badlyexecutedsafetytest"initiatedthedisaster.Asuddensurgeofpowertriggeredasteamexplosionthatrupturedthereactorvessel.Thisallowedthefurtherviolentfuel
7、-steaminteractionsthatdestroyedthereactorcoreandseverelydamagedthereactorbuilding.Asregardstheradiationcontainment,liketheThreeMileIslandplant,theFukushimareactorshavethreebarriersdesignedtopreventradiationleakage,includingmetalcladdingsurroundingthenucl