切尔诺贝利事故.docx

切尔诺贝利事故.docx

《切尔诺贝利事故.docx》由会员分享，可在线阅读，更多相关《切尔诺贝利事故.docx（6页珍藏版）》请在冰豆网上搜索。

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