切尔诺贝利事故.docx
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切尔诺贝利事故.docx
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切尔诺贝利事故
ChernobylAccident
NuclearIssuesBriefingPaper22
March2001
∙TheChernobylaccidentin1986wastheresultofaflawedreactordesignthatwasoperatedwithinadequatelytrainedpersonnelandwithoutproperregardforsafety.
∙Theresultingsteamexplosionandfirereleasedatleastfivepercentoftheradioactivereactorcoreintotheatmosphereanddownwind.
∙Some31peoplewerekilled,andtherehavesincebeenaroundtendeathsfromthyroidcancerduetotheaccident.
∙AnauthoritativeUNreportin2000concludedthatthereisnoscientificevidenceofanysignificantradiation-relatedhealtheffectstomostpeopleexposed.
TheApril1986disasterattheChernobylnuclearpowerplantintheUkrainewastheproductofaflawedSovietreactordesigncoupledwithseriousmistakesmadebytheplantoperatorsinthecontextofasystemwheretrainingwasminimal.ItwasadirectconsequenceofColdWarisolationandtheresultinglackofanysafetyculture.
NB:
"Chernobyl"isthewell-knownRussiannameforthesite;"Chornobyl"ispreferredbyUkraine.
Map.clicktoenlarge
Reactordiagram.clicktoenlarge
Source:
OECDNEA
TheaccidentdestroyedtheChernobyl-4reactorandkilled30people,including28fromradiationexposure.Afurther209onsiteweretreatedforacuteradiationpoisoningandamongthese,134caseswereconfirmed(allofwhomrecovered).Nobodyoff-sitesufferedfromacuteradiationeffects.However,largeareasofBelarus,Ukraine,Russiaandbeyondwerecontaminatedinvaryingdegrees.
TheChernobyldisasterwasauniqueeventandtheonlyaccidentinthehistoryofcommercialnuclearpowerwhereradiation-relatedfatalitiesoccurred.*
*Therehavebeenfatalitiesinmilitaryandresearchreactorcontexts,egTokai-mura.
Theaccident
On25April,priortoaroutineshut-down,thereactorcrewatChernobyl-4beganpreparingforatesttodeterminehowlongturbineswouldspinandsupplypowerfollowingalossofmainelectricalpowersupply.SimilartestshadalreadybeencarriedoutatChernobylandotherplants,despitethefactthatthesereactorswereknowntobeveryunstableatlowpowersettings.
Aseriesofoperatoractions,includingthedisablingofautomaticshutdownmechanisms,precededtheattemptedtestearlyon26April.Asflowofcoolantwaterdiminished,poweroutputincreased.Whentheoperatormovedtoshutdownthereactorfromitsunstableconditionarisingfrompreviouserrors,apeculiarityofthedesigncausedadramaticpowersurge.
Thefuelelementsrupturedandtheresultantexplosiveforceofsteamliftedoffthecoverplateofthereactor,releasingfissionproductstotheatmosphere.Asecondexplosionthrewoutfragmentsofburningfuelandgraphitefromthecoreandallowedairtorushin,causingthegraphitemoderatortoburstintoflames.
Thereissomedisputeamongexpertsaboutthecharacterofthissecondexplosion.Thegraphiteburnedforninedays,causingthemainreleaseofradioactivityintotheenvironment.Atotalofabout12x1018Bqofradioactivitywasreleased.Seealsoappendedsequenceofevents.
Some5000tonnesofboron,dolomite,sand,clayandleadweredroppedontotheburningcorebyhelicopterinanefforttoextinguishtheblazeandlimitthereleaseofradioactiveparticles.
clicktoenlarge
ThedamagedChernobylunit4reactorbuilding
Immediateimpact
Itisestimatedthatallofthexenongas,abouthalfoftheiodineandcaesium,andatleast5%oftheremainingradioactivematerialintheChernobyl-4reactorcorewasreleasedintheaccident.Mostofthereleasedmaterialwasdepositedclosebyasdustanddebris,butthelightermaterialwascarriedbywindovertheUkraine,Belarus,RussiaandtosomeextentoverScandinaviaandEurope.
Themaincasualtieswereamongthefirefighters,includingthosewhoattendedtheinitialsmallfiresontheroofoftheturbinebuilding.Allthesewereputoutinafewhours.
Thenexttaskwascleaninguptheradioactivityatthesitesothattheremainingthreereactorscouldberestarted,andthedamagedreactorshieldedmorepermanently.About200,000people("liquidators")fromallovertheUSSRwereinvolvedintherecoveryandcleanupduring1986and1987.Theyreceivedhighdosesofradiation,around100millisieverts.Some20,000ofthemreceivedabout250mSvandafewreceived500mSv.Later,thenumberofliquidatorsswelledtoover600,000butmostofthesereceivedonlylowradiationdoses.
Manychildreninthesurroundingareaswereexposedtoradiationdosessufficienttoleadtothyroidcancers(usuallynotfatalifdiagnosedandtreatedearly).Initialradiationexposureincontaminatedareaswasduetoshort-livediodine-131,latercaesium-137wasthemainhazard(botharefissionproductsdispersedfromthereactorcore).On2-3May,some45,000residentswereevacuatedfromwithina10kmradiusoftheplant,notablyfromtheplantoperators'townofPripyat.On4May,allthoselivingwithina30kilometreradius-afurther116000people-wereevacuatedandlaterrelocated.About1,000ofthesehavesincereturnedunofficiallytolivewithinthecontaminatedzone.Mostofthoseevacuatedreceivedradiationdosesoflessthan50mSv,althoughafewreceived100mSvormore.
Intheyearsfollowingtheaccidentafurther210000peoplewereresettledintolesscontaminatedareas,andtheinitial30kmradiusexclusionzone(2800km2)wasmodifiedandextendedtocover4300squarekilometres.
Environmentalandhealtheffects
SeveralorganisationshavereportedontheimpactsoftheChernobylaccident,butallhavehadproblemsassessingthesignificanceoftheirobservationsbecauseofthelackofreliablepublichealthinformationbefore1986.In1989theWorldHealthOrganisation(WHO)firstraisedconcernsthatlocalmedicalscientistshadincorrectlyattributedvariousbiologicalandhealtheffectstoradiationexposure.
AnInternationalAtomicEnergyAgency(IAEA)studyinvolvingmorethan200expertsfrom22countriespublishedin1991wasmoresubstantial.Intheabsenceofpre-1986dataitcomparedacontrolpopulationwiththoseexposedtoradiation.Significanthealthdisorderswereevidentinbothcontrolandexposedgroups,but,atthatstage,nonewasradiationrelated.
SubsequentstudiesintheUkraine,RussiaandBelaruswerebasedonnationalregistersofover1millionpeoplepossiblyaffectedbyradiation.Theseconfirmedarisingincidenceofthyroidcanceramongexposedchildren.Latein1995,theWorldHealthOrganisationlinkednearly700casesofthyroidcanceramongchildrenandadolescentstotheChernobylaccident,andamongthesesome10deathsareattributedtoradiation.
Sofarnoincreaseinleukaemiaisdiscernible,butthisisexpectedtobeevidentinthenextfewyearsalongwithagreater,thoughnotstatisticallydiscernible,incidenceofothercancers.TherehasbeennosubstantiatedincreaseattributabletoChernobylincongenitalabnormalities,adversepregnancyoutcomesoranyotherradiation-induceddiseaseinthegeneralpopulationeitherinthecontaminatedareasorfurtherafield.
Pathsofradiationexposure.clicktoenlarge
Psycho-socialeffectsamongthoseaffectedbytheaccidentareemergingasamajorproblem,andaresimilartothosearisingfromothermajordisasterssuchasearthquakes,floodsandfires.
ThemostrecentandauthoritativeUNreporthasconfirmedthatthereisnoscientificevidenceofanysignificantradiation-relatedhealtheffectstomostpeopleexposedtotheChernobyldisaster.TheUNSCEAR*2000ReportisconsistentwithearlierWHOfindings.Thereportpointstosome1,800casesofthyroidcancer,but"apartfromthisincrease,thereisnoevidenceofamajorpublichealthimpactattributabletoradiationexposure14yearsaftertheaccident.Thereisnoscientificevidenceofincreasesinoverallcancerincidenceormortalityorinnon-malignantdisordersthatcouldberelatedtoradiationexposure."Asyetthereislittleevidenceofanyincreaseinleukaemiaappearstobeincreased,evenamongclean-upworkerswhereitmightbemostexpected.However,theseworkersremainatincreasedriskofcancerinthelongterm.
*theUnitedNationsScientificCommissionontheEffectsofAtomicRadiation,whichistheUNbodywithamandatefromtheGeneralAssemblytoassessandreportlevelsandhealtheffectsofexposuretoionizingradiation.
SomeexaggeratedfigureshavebeenpublishedregardingthedeathtollattributabletotheChernobyldisaster.ApublicationbytheUNOfficefortheCoordinationofHumanitarianAffairs(OCHA)entitledChernobyl-acontinuingcatastrophelentsupporttothese.However,theChairmanofUNSCEARmadeitclearthat"thisreportisfullofunsubstantiatedstatementsthathavenosupportinscientificassessments."
CopiesoftheNovember1995WHOstatementandtheConclusionsfromtheUNSCEAR2000reportonthehealtheffectsofChernobylareappended,withtheabstractofamajor1996paperonlong-termhealtheffects.
Chernobyltoday
TheChernobylunit4isnowenclosedinalargeconcreteshelterwhichwaserectedquicklytoallowcontinuingoperationoftheotherreactorsattheplant.However,thestructureisneitherstrongnordurableandthereareplansforitsreconstruction.TheinternationalShelterImplementationPlaninvolvedraisingUS$715millionforremedialworkincludingremovalofthefuel-containingmaterials.Someworkontheroofhasalreadybeencarriedout.
InMarch2001aUS$36millioncontractwassignedforconstructionofaradioactivewastemanagementfacilitytotreatspentfuelandotheroperationalwastes,aswellasmaterialfromdecommissioningunits1-3.
Intheearly1990ssomeUS$400millionwasspentonimprovementstothe
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