Chernobyl disaster

1. up close andstill dangersChernobyl'sreactorforthe scene at the total meltdowntwenty-fiveyearsago
exactlythe crisisthatscientistsinJapanhave beenbattlingtoavoidaDNC Jessissue itwasandremains
the world'sworstnuclearaccidentdozensof people were killedthousandsmore diedfromcancer
amongthemsoldiersordertothe front line of the cleanupaquarterof a centuryon we were given
extremelyrare accessintothe contaminatedreactive blockbutonlybrieflyandinspecial clothingface
masksthat remainonsite the radiationreabsorbedwascarefullymonitoredpassage of time means
levelsare muchlowernowacceptsdeepinsidethe concrete intoreactorbutthe multi-core itself and
thisisthe control rooma Fri Oct 24 the place where the menwhowere runningitthatI were working
and fora while theyknew thatsomethingwasgoingwrongbuttheydidn'trealize thatwouldbe a
massive explosioninthe mainhall just50 metersawayand the whole reactorwasin meltdownunit4's
in1:18 he replace andbecause itsradioactive debrisisstill notpropertycontainsitremainsathreatto
the widerworlditlooksbetterforthe outside andthe inside if you're able togointothe central hall
todayand lookout youwouldfindthatthere'sholesthe size apicture windowsatvariouslocationsin
the objectshelteritsitsoit's a problemthatneedstobe dealtwithstructure will graduallybe
completedwiththe restthere are ambitiousbutexpensiveplanstobuildavastnew coverfor the
reactor to theirthiswouldfinallymake channelsafe forahundredyearscontaininganyradiationif the
reactor buildingcollapsedthe cityof trippyOct fromwhich50,000 people fledinafternoonisstill
contaminatedandabandone lookatthe clock onDrake Luke offeredhere andhadbeendue to
cooperate reactorfor that dayprettychippyIQ's byC kindergartenwhere mychildrenstayedbutIsee
the billionsformyFrance histo leave some of themare no longerwithussothisis thisemotional desist
thisisset there isno signupthe twenty-mileexclusionzone aroundthe reactorbeingliftedareminder
that whennuclearpowergoeswrongitcan go verybadlywrongDaniel SanfordBBCNewsChernobyl
reactor (rɪˈæktə) (Chemistry) chemasubstance,suchasa reagent,thatundergoesareaction2.
(NuclearPhysics) shortfornuclearreactor3. (Chemistry)avessel,espone inindustrial use,inwhicha
chemical reactiontakesplace
meltdown(ˈmɛltˌdaʊn) (NuclearPhysics)(inanuclearreactor) the meltingof the fuel rodsasa resultof
a defectinthe coolingsystem,withthe possible escapeof radiationintothe environment2.a sudden
disastrousfailure withpotential forwidespreadharm, asa stock-exchange crash
DNC 1. DemocraticNational Committee 2.Democratic National Convention
jess(dʒɛs) falconry1.(Falconry) ashort leatherstrap,one endof whichispermanentlyattachedtothe
legof a hawkor falconwhile the othercanbe attached to a leash
issue (ˈɪʃjuː) 1. the act of sendingorgivingoutsomething; supply;delivery3.(Banking&Finance) the
numberof identical items,suchasbanknotesorsharesin a company,that become available ata
particulartime 4. the act of emerging;outflow;discharge
nuclear (ˈnjuːklɪə) 1. (General Physics) of,concerned with,orinvolvingthe nucleusof anatom: nuclear
fission. 4. (General Physics) of,concernedwith,oroperatedbyenergyfromfissionorfusionof atomic
nuclei:anuclearweapon.

2. Order (tr) to give a commandto (a personor animal todo or be something)
Contaminate to make (something) dangerous,dirty,orimpure byaddingsomethingharmfulor
undesirabletoit– polluted –забруднений
reabsorb 1. To absorbagain. 2. To accommodate or acceptagain,as intoa groupor category:The
economycannotreabsorball of the refugeesintothe workforce. Toundergoresorption. Вбирати
monitor 12. to observe,record,ordetect(anoperationorcondition) withinstrumentsthathave no
effectuponthe operationorcondition. 13.to oversee,supervise,orregulate. 14. to watch closelyfor
purposesof control,surveillance,etc.;keeptrackof.контролювати
cleanup 1. the act or processof cleaningup.
Multi core багатоядерний
debrisalsodé·brisa.The scatteredremainsof somethingbrokenor destroyed;rubble orwreckage.b.
Carelesslydiscardedrefuse;litte брухт
Chernobyl Accident1986
The Chernobyl accidentin1986 was the resultof a flawedreactordesignthatwasoperatedwith
inadequatelytrainedpersonnel.
The resultingsteamexplosionandfiresreleasedatleast5% of the radioactive reactorcore intothe
atmosphere anddownwind –some 5200 PBq (I-131 eq).
Two Chernobyl plantworkersdiedonthe nightof the accident,anda further28 people diedwithina
fewweeksasa resultof acute radiationpoisoning.
UNSCEARsays that apart fromincreasedthyroidcancers,"there isnoevidenceof amajor publichealth
impactattributable toradiationexposure 20years afterthe accident."
Resettlementof areasfromwhichpeoplewere relocatedis ongoing.In2011 Chernobyl wasofficially
declaredatouristattraction.
The April 1986 disasteratthe ChernobylanuclearpowerplantinUkraine wasthe productof a flawed
Sovietreactordesigncoupledwithseriousmistakesmade bythe plantoperatorsb. Itwasa direct
consequence of ColdWarisolationandthe resultinglackof any safetyculture.
The accidentdestroyedthe Chernobyl4reactor, killing30 operatorsandfiremenwithinthree months
and several furtherdeathslater.One personwaskilledimmediatelyandaseconddiedinhospital soon
afteras a resultof injuriesreceived.Anotherpersonisreportedtohave diedatthe time froma
coronary thrombosisc.Acute radiationsyndrome (ARS) wasoriginallydiagnosedin237 people on-site
and involved withthe clean-upanditwaslaterconfirmedin134 cases.Of these,28 people diedasa
resultof ARS withinafewweeksof the accident.Nineteenmore subsequentlydiedbetween1987 and
2004 but theirdeathscannotnecessarilybe attributedtoradiation exposured.Nobodyoff-site suffered

3. fromacute radiationeffectsalthoughalarge proportionof childhoodthyroidcancersdiagnosedsince
the accidentislikelytobe due to intake of radioactive iodine falloutd.Furthermore,large areasof
Belarus,Ukraine,Russiaandbeyondwere contaminatedinvaryingdegrees.See alsosectionsbelowand
Chernobyl AccidentAppendix2:HealthImpacts.
The Chernobyl disasterwasaunique eventandthe onlyaccidentinthe historyof commercial nuclear
powerwhere radiation-relatedfatalitiesoccurrede.However,the designof the reactorisunique andin
that respectthe accidentisthusof little relevance tothe restof the nuclearindustryoutside the then
EasternBloc. However,itledtomajorchangesinsafetyculture andin industrycooperation,particularly
betweenEastandWestbefore the endof the SovietUnion.FormerPresidentGorbachevsaidthatthe
Chernobyl accidentwasamore importantfactor inthe fall of the SovietUnionthanPerestroika –his
program of liberal reform.
The Chernobyl site andplant
The Chernobyl PowerComplex,lyingabout130 km northof Kiev,Ukraine,andabout20 km southof the
borderwithBelarus,consistedof fournuclearreactorsof the RBMK-1000 design(see informationpage
on RBMK Reactors),units1 and 2 beingconstructedbetween1970 and1977, while units3and 4 of the
same designwere completedin1983. Two more RBMK reactors were underconstructionatthe site at
the time of the accident.Tothe southeastof the plant,anartificial lake of some 22 square kilometres,
situatedbesidethe riverPripyat,atributaryof the Dniepr,wasconstructedtoprovide coolingwaterfor
the reactors.
Thisarea of Ukraine isdescribedasBelarussian-type woodlandwithalow populationdensity.About3
km awayfrom the reactor,in the newcity,Pripyat,there were 49,000 inhabitants.The oldtownof
Chornobyl,whichhadapopulationof 12,500, is about15 km to the southeastof the complex.Withina
30 km radiusof the powerplant,the total populationwasbetween115,000 and 135,000.
Source:OECD NEA
The RBMK-1000 is a Soviet-designedandbuiltgraphite moderatedpressure tube typereactor,using
slightlyenriched(2%U-235) uraniumdioxidefuel.Itisa boilinglightwaterreactor,withtwoloops
feedingsteamdirectlytothe turbines,withoutaninterveningheatexchanger.Waterpumpedtothe
bottomof the fuel channelsboilsasitprogressesupthe pressure tubes,producingsteamwhichfeeds
two500 MWe turbines.The wateracts as a coolantand alsoprovidesthe steamusedtodrive the
turbines.The vertical pressuretubescontainthe zirconiumalloycladuraniumdioxide fuel aroundwhich
the coolingwaterflows.The extensionsof the fuel channelspenetrate the lowerplate andthe cover
plate of the core and are weldedtoeach.A speciallydesignedrefuellingmachineallowsfuelbundlesto
be changedwithoutshuttingdownthe reactor.
The moderator,whose functionistoslow downneutronstomake themmore efficientinproducing
fissioninthe fuel,isgraphite,surroundingthe pressure tubes.A mixture of nitrogenandheliumis
circulatedbetweenthe graphite blockstopreventoxidationof the graphite andtoimprove the
transmissionof the heatproducedbyneutroninteractionsinthe graphite tothe fuel channel.The core

4. itself isabout7 m highand about12 m indiameter.Ineachof the two loops,there are fourmain
coolantcirculatingpumps,one of whichisalwaysonstandby.The reactivityorpowerof the reactor is
controlledbyraisingorlowering211 control rods,which,whenloweredintothe moderator,absorb
neutronsandreduce the fissionrate.The poweroutputof thisreactoris 3200 MW thermal,or1000
MWe. Varioussafetysystems,suchasan emergencycore coolingsystem, wereincorporatedintothe
reactor design.
One of the mostimportantcharacteristicsof the RBMK reactor isthat it it can possessa'positive void
coefficient',where anincrease insteambubbles('voids') isaccompaniedbyanincrease incore
reactivity(see informationpage onRBMK Reactors).Assteamproductioninthe fuel channelsincreases,
the neutronsthatwouldhave beenabsorbedbythe denserwaternow produce increasedfissioninthe
fuel.There are othercomponentsthatcontribute tothe overall powercoefficientof reactivity,butthe
voidcoefficientisthe dominantone inRBMKreactors.The voidcoefficientdependsonthe composition
of the core – a newRBMK core will have a negative voidcoefficient.However,atthe time of the
accidentat Chernobyl 4,the reactor's fuel burn-up,control rodconfigurationandpowerlevel ledtoa
positive voidcoefficientlarge enoughtooverwhelmall otherinfluencesonthe powercoefficient.
The 1986 Chernobyl accident
On 25 April,priortoa routine shutdown,the reactorcrew atChernobyl 4beganpreparingfora testto
determine howlongturbineswouldspinandsupplypowertothe maincirculatingpumpsfollowinga
lossof main electrical powersupply.ThistesthadbeencarriedoutatChernobyl the previousyear,but
the powerfromthe turbine randowntoo rapidly,sonew voltage regulatordesignswere tobe tested.
A seriesof operatoractions,includingthe disablingof automaticshutdownmechanisms,precededthe
attemptedtestearlyon26 April.Bythe time that the operatormovedtoshut downthe reactor,the
reactor wasin an extremelyunstable condition.A peculiarityof the designof the control rodscauseda
dramaticpowersurge as theywere insertedintothe reactor(see Chernobyl AccidentAppendix 1:
Sequence of Events).
The interactionof veryhotfuel withthe coolingwaterledtofuel fragmentationalongwithrapidsteam
productionandan increase inpressure.The designcharacteristicsof the reactorwere suchthat
substantial damage toeventhree orfourfuel assembliescan – and did – resultinthe destructionof the
reactor.The overpressure causedthe 1000 t cover plate of the reactor to become partiallydetached,
rupturingthe fuel channelsandjammingall the control rods,whichbythattime were onlyhalfway
down.Intense steamgenerationthenspreadthroughoutthe wholecore (fedbywaterdumpedintothe
core due to the rupture of the emergencycoolingcircuit) causingasteamexplosionandreleasingfission
productsto the atmosphere.Abouttwotothree secondslater,asecondexplosionthrew outfragments
fromthe fuel channelsandhotgraphite.There issome disputeamongexpertsaboutthe characterof
thissecondexplosion,butitislikelytohave beencausedbythe productionof hydrogen fromzirconium-
steamreactions.
Two workersdiedasa resultof these explosions.The graphite (aboutaquarterof the 1200 tonnesof it
was estimatedtohave beenejected) andfuel became incandescentandstartedanumberof firesf,

5. causingthe mainrelease of radioactivityintothe environment.A total of about14 EBq (14 x 1018 Bq) of
radioactivitywasreleased,overhalf of itbeingfrombiologically-inertnoble gases.*
*The figure of 5.2 EBq isalsoquoted,thisbeing"iodine-131equivalent"- 1.8 EBq iodine and85 PBq Cs-
137 multipliedby40 due its longevity,andignoringthe 6.5EBq xenon-33and some minoror short-lived
nuclides.
About200-300 tonnesof waterper hourwas injectedintothe intacthalf of the reactor usingthe
auxiliaryfeedwaterpumpsbutthiswasstoppedafterhalf aday owingtothe danger of it flowinginto
and floodingunits1and2. Fromthe secondtotenthday afterthe accident,some 5000 tonnesof boron,
dolomite,sand,clayandleadwere droppedontothe burningcore by helicopterinaneffortto
extinguishthe blaze andlimitthe release of radioactive particles.
The damagedChernobyl unit4reactor building
The 1991 reportbythe State Committee onthe Supervisionof SafetyinIndustryandNuclearPoweron
the root cause of the accidentlookedpastthe operatoractions.Itsaidthat while itwascertainlytrue
the operatorsplacedtheirreactorina dangerouslyunstable condition(infact ina conditionwhich
virtuallyguaranteedanaccident) itwasalsotrue that in doingsotheyhad not infact violatedanumber
of vital operatingpoliciesandprinciples,sincenosuchpoliciesandprincipleshadbeenarticulated.
Additionally,the operatingorganisationhadnotbeenmade aware eitherof the specificvital safety
significance of maintainingaminimumoperatingreactivitymargin,orthe general reactivity
characteristicsof the RBMK whichmade low poweroperationextremelyhazardous.
Immediate impactof the Chernobyl accident
The accidentcausedthe largestuncontrolledradioactive releaseintothe environmenteverrecordedfor
any civilianoperation,andlarge quantitiesof radioactive substanceswerereleasedintothe airforabout
10 days.This causedserioussocial andeconomicdisruptionforlarge populationsinBelarus,Russiaand
Ukraine.Tworadionuclides,the short-livediodine-131andthe long-livedcaesium-137,were particularly
significantforthe radiationdose theydeliveredtomembersof the public.
It isestimatedthatall of the xenongas,about half of the iodine andcaesium, andat least5% of the
remainingradioactivematerialinthe Chernobyl 4reactorcore (whichhad192 tonnesof fuel) was
releasedinthe accident.Most of the releasedmaterial wasdepositedclose byasdustand debris,but
the lightermaterial wascarriedbywindoverUkraine,Belarus,Russiaandtosome extentover
ScandinaviaandEurope.
The casualtiesincludedfirefighterswhoattendedthe initial firesonthe roof of the turbine building.All
these were putoutin a fewhours,butradiationdosesonthe firstday were estimatedtorange up to
20,000 millisieverts(mSv),causing28deaths – six of whichwere firemen–by the endof July1986.
The nexttask wascleaningupthe radioactivityatthe site so thatthe remainingthree reactorscouldbe
restarted,andthe damagedreactor shieldedmore permanently.About200,000 people ('liquidators')
fromall over the SovietUnionwere involvedinthe recoveryandclean-upduring1986 and 1987. They

6. receivedhighdosesof radiation,averagingaround100 millisieverts.Some 20,000 of themreceived
about250 mSvand a fewreceived500 mSv.Later, the numberof liquidatorsswelledtoover600,000
but mostof these receivedonlylowradiationdoses.The highestdoseswere receivedbyabout1000
emergencyworkersandon-sitepersonnelduringthe firstdayof the accident.The effectsof radiation
exposure fall intotwomainclasses:deterministiceffects,where the effectiscertaintooccur under
givenconditions(e.g.individualsexposedtoseveral graysoverashort periodof time will definitely
sufferAcute RadiationSyndrome);andstochasticeffects,where the effectmayormay notoccur (e.g.
an increase inradiationexposure mayormay notinduce a cancer ina particularindividual butif a
sufficientlylarge populationreceivearadiationexposureabove acertainlevel,anincrease inthe
incidence of cancermaybecome detectable inthatpopulation).UNSCEAR, 2011.
Initial radiationexposureincontaminatedareaswasdue to short-livediodine-131;latercaesium-137
was the mainhazard.(Bothare fissionproductsdispersedfromthe reactorcore,withhalf livesof 8days
and 30 years,respectively.1.8EBq of I-131 and 0.085 EBq of Cs-137 were released.) Aboutfive million
people livedinareasof Belarus,RussiaandUkraine contaminated(above37kBq/m2 Cs-137 insoil) and
about400,000 livedinmore contaminatedareasof strictcontrol byauthorities(above 555kBq/m2 Cs-
137).
* supposedlycorrelatingwith1mSv/yrdose withcontinuousexposure.About23% of Belaruswas
contaminatedtothislevel,with7%of Ukraine and 1.5% of EuropeanRussia.
The plant operators'townof Pripyatwasevacuatedon27 April (45,000 residents).By14 May, some
116,000 people thathadbeenlivingwithina30-kilometre radiushadbeenevacuatedandlater
relocated.About1000 of these returnedunofficiallytolive withinthe contaminatedzone.Mostof those
evacuatedreceived radiationdosesof lessthan50 mSv,although a few received100mSv or more.
In the yearsfollowingthe accident,afurther220,000 people were resettledintolesscontaminated
areas,and the initial 30 km radiusexclusionzone (2800 km2) was modifiedand extendedtocover4300
square kilometres.Thisresettlementwasdue toapplicationof acriterionof 350 mSvprojectedlifetime
radiationdose,thoughinfactradiationinmostof the affectedarea(apartfromhalf a square kilometre)
fell rapidlysothat average doseswere lessthan50% above normal backgroundof 2.5 mSv/yr.See also
followingsectiononResettlement.
Environmental andhealtheffectsof the Chernobyl accident
Several organisationshave reportedonthe impactsof the Chernobyl accident,butall have had
problemsassessingthe significance of theirobservationsbecause of the lackof reliable public health
informationbefore 1986.
In 1989, the WorldHealthOrganization(WHO) firstraisedconcernsthatlocal medical scientistshad
incorrectly attributedvariousbiological andhealtheffectstoradiationexposureg.Followingthis,the
Governmentof the USSR requestedthe International AtomicEnergyAgency(IAEA) tocoordinate an
international experts'assessmentof accident'sradiological,environmental andhealthconsequencesin
selectedtownsof the mostheavilycontaminatedareasinBelarus,Russia,andUkraine.BetweenMarch

7. 1990 and June 1991, a total of 50 fieldmissionswere conductedby200 expertsfrom25 countries
(includingthe USSR), sevenorganisations,and11 laboratories3.In the absence of pre-1986 data,it
compareda control populationwiththose exposedtoradiation.Significanthealthdisorderswere
evidentinbothcontrol andexposedgroups,but,atthatstage,none was radiationrelated.
Pathsof radiationexposureh
SubsequentstudiesinUkraine,RussiaandBelaruswere basedonnational registersof overone million
people possiblyaffectedbyradiation.By2000, about4000 cases of thyroidcancer hadbeendiagnosed
inexposedchildren.However,the rapidincreaseinthyroidcancersdetectedsuggeststhatsome of itat
leastisan artifact of the screeningprocess.Thyroidcancerisusuallynotfatal if diagnosedandtreated
early.
In February2003, the IAEA establishedthe ChernobylForum, incooperationwithsevenotherUN
organisationsaswell asthe competentauthoritiesof Belarus,the RussianFederationandUkraine.In
April 2005, the reportspreparedbytwo expertgroups – "Environment",coordinatedbythe IAEA,and
"Health",coordinatedbyWHO – were intensivelydiscussedbythe Forumandeventuallyapprovedby
consensus.The conclusionsof this2005 Chernobyl Forumstudy(revisedversionpublished2006i) are in
line withearlierexpertstudies,notablythe UNSCEAR2000 reportj whichsaidthat "apart fromthis
[thyroidcancer] increase,there isnoevidence of amajorpublichealthimpactattributable toradiation
exposure 14years afterthe accident.There isno scientificevidenceof increasesinoverall cancer
incidence ormortalityorinnon-malignantdisordersthatcouldbe relatedtoradiationexposure."Asyet
there islittle evidenceof anyincrease inleukaemia,evenamongclean-upworkerswhere itmightbe
mostexpected.However,theseworkers –where highdoses mayhave beenreceived –remainat
increasedriskof cancerin the longterm.Apart fromthese,the UnitedNationsScientificCommitteeon
the Effectsof AtomicRadiation(UNSCEAR) saysthat"the great majorityof the populationisnotlikelyto
experience serioushealthconsequencesasaresultof radiationfromthe Chernobyl accident.Many
otherhealthproblemshave beennotedinthe populationsthatare not relatedtoradiationexposure."
The Chernobyl Forumreportsaysthat people inthe areahave sufferedaparalysingfatalismdue to
mythsand misperceptionsaboutthe threatof radiation,whichhascontributedtoaculture of chronic
dependency.Some "tookonthe role of invalids."Mental healthcoupledwithsmokingandalcohol
abuse isa verymuchgreaterproblemthanradiation,butworstof all at the time wasthe underlying
level of healthandnutrition.Apartfromthe initial 116,000, relocationsof people wereverytraumatic
and didlittle toreduce radiationexposure,whichwaslow anyway.Psycho-social effectsamongthose
affectedbythe accidentare similartothose arisingfromothermajordisasterssuchas earthquakes,
floodsandfires.
Accordingto the mostup-to-date estimateof UNSCEAR,the average radiationdose due tothe accident
receivedbyinhabitantsof 'strictradiationcontrol'areas(population216,000) inthe years 1986 to 2005
was 31 mSv(overthe 20-year period),andinthe 'contaminated'areas(population6.4million) it
averaged9 mSv,a minorincrease overthe dose due tobackgroundradiationoverthe same period
(about50 mSv)4.

8. The numbersof deathsresultingfromthe accidentare coveredmostfullyinthe accountof health
effectsisprovidedbyanannex tothe UNSCEAR 2008 report,releasedin2011.5
Some exaggeratedfigureshave beenpublishedregardingthe deathtoll attributable tothe Chernobyl
disaster.A publicationbythe UN Office forthe Coordinationof HumanitarianAffairs(OCHA)6lent
supportto these. However,the Chairmanof UNSCEARmade itclearthat "thisreportisfull of
unsubstantiatedstatementsthathave nosupportinscientificassessments"k,andthe Chernobyl Forum
reportalsorepudiatesthem.
A particularlysadeffectof the accidentwasthatsome physiciansinEurope advisedpregnantwomento
undergoabortionsonaccountof radiationexposure,eventhoughthe levelsconcernedwere vastly
belowthose likelytohave teratogeniceffects.The foetal deathtoll fromthisislikelyverymuchgreater
than directlyfromthe accident.
UNSCEARin 2011 concludes:Insummary,the effectsof the Chernobylaccidentare manyandvaried.
Early deterministiceffectscanbe attributedtoradiationwithahighdegree of certainty,while forother
medical conditions,radiationalmostcertainlywasnotthe cause.In between,there wasawide
spectrumof conditions.Itisnecessarytoevaluate carefullyeachspecificconditionandthe surrounding
circumstancesbefore attributingacause.5