“Stress Tests” for UK non-Power Generating Nuclear Facilities ...

Office for Nuclear RegulationAn agency of HSE

FinalReportonStressTestsforUKnonPowerGeneratingNuclearFacilities

Stress Tests for UK non-Power Generating Nuclear Facilities

Final Report

May 2012


FinalReportonStressTestsforUKnonPowerGeneratingNuclearFacilities

Crowncopyright2012

FirstpublishedMay2012

ONRReportONRUKSTREP12001Revision1

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ExecutiveSummary Introduction

Following theeventsatFukushima, Japan,on11March2011, thenuclear industry in theUK respondedquickly to reviewUKnuclear installations against seismic and floodinghazards.On14March2011,HMChiefInspectorofNuclearInstallationswasaskedbytheSecretaryofStateforEnergyandClimateChangetoproduceaninterimreportbythemiddleofMay2011,withafinalreportsixmonthslateronthelessonsthatcouldbe learnttoenhancethesafetyoftheUKnuclear industry.The interimandfinalreportswerepublished in May and October 2011 respectively and contained a number of important conclusionsregarding the UK nuclear industry and regulatory regime, as well as a significant number ofrecommendations for further work to determine whether there are any reasonably practicableimprovementsthatcanbemade.Afurtherreportisplannedfortheautumnof2012inwhichtheOfficeforNuclearRegulation(ONR)willreportonprogressindealingwiththoserecommendations.

On 2425March 2011 the European Council (EC) requested a review of safety at all European nuclearpowerplants(NPP)andtheEuropeanNuclearSafetyRegulatorsGroup(ENSREG)producedaspecificationand a plan for this review based on preliminary work carried out by theWestern European NuclearRegulatorsAssociation(WENRA).Thereviewsarecommonlyreferredtoasthestresstests.

GiventhattheECstresstestsonly focusonNPPs,HMChief InspectorofNuclear Installationsdecidedtoextend the stress tests process to all other licensed nuclear installationswithin theUK. These licensednuclear installations are designated as nonpower generating nuclear facilities (NPGNF) in this report.SeveralothercountrieswithintheEuropeanUnionhavealsoplannedtoapplythestresstestsprocesstosomeNPGNF.

Stresstestsrequirements

The ENSREG specification defines the stress tests as a targeted reassessment of the safetymargins ofnuclear power plants in the light of the eventswhich occurred at Fukushima; namely extreme naturaleventschallengingplant safety functionsand leading to severeaccidentsand theneed to invoke severeaccidentmanagement procedures. The ENSREG requirements were defined for NPPs only and do notincludeothernuclear installations,andONRrecognisesthatsomeaspectsofthestresstestsspecificationmaynotapplytoeveryNPGNFinastraightforwardmanneror,insomecases,atall.

Thestresstestsrequirementsessentiallyfollowadefenceindepthapproachlookingfirstlyatthedesigntopreventearthquakes,floodandextremeweathercausingsafetyproblemsatsites.Irrespectiveofhowgoodthesepreventativemeasuresmightbe, the stress tests then call fora systematicexaminationof lossofelectricalsuppliesandlossofcoolingcapability.Again,nomatterhowrobustthesesystemsare,thestresstests specification goes on to require consideration of severe accidents and themanagement of thesesevereaccidents.Theprincipalaimforallthelevelsofdefenceindepthrepresentedinthestresstestsistoidentifyanyadditionalmeasuresorprovisionstoenhancesafety.Thisaim isentirelycompatiblewiththephilosophyofcontinuousimprovementembeddedwithintheUKregulatorysystem.

Rangeandnatureofnonpowergeneratingnuclearfacilities

ThefacilitiescapturedwithinthescopeoftheNPGNFstresstestsvary intermsofthenatureofactivitiesundertaken, the hazards associatedwith those activities and the potential hazardous consequences atthosefacilities.Forexample,thisreportcoverstheSellafieldnuclearsite,oneofthebiggestgroupingsofnuclear installationswithinEurope,aswellassmall licensedsiteswhichareclose tocompletionof their


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decommissioningactivities.Additionally,NPGNF include facilitiesdedicatedtothe fuelcycle, installationstosupport thenucleardeterrent,andconventionalnuclearsubmarinesandsites forradioactivematerialstorage.

Certainof the sites in theDefenceNuclearProgrammearemanagedby theMinistryofDefence (MoD)itself and activities there are exempted from some parts of civil regulation.Wherever exemptions ordisapplicationsofcivil legislationexist,theDefenceNuclearSafetyRegulator(DNSR)overseesasystemofregulationofthoseMoDdutyholderswhodirectlycontrolnuclearactivities.DNSR iscarryingout itsownassessment,equivalenttotheFukushimastresstests.Inthisreport,ONRhasonlyconsideredthoseaspectsofthedefencenuclearprogrammethatarecarriedoutbylicenseesandtheimplicationsfornuclearsafetyregarding those activities and facilities to which the Nuclear Installations Act 1965 and Radiation(EmergencyPreparednessandPublicInformation)Regulations2001(REPPIR)apply.

ConductofthestresstestsandONRreview

TheNationalReporton EuropeanCouncil StressTests forUKNuclearPowerPlantswaspublishedon4January2012.This current report is the finalUK stress tests report andpresents the results from thestresstestsasappliedtoUKNPGNF.Incarryingoutthestresstests,andindependentregulatoryreviewofthosestresstests, it isrecognisedbyONRand theUKnuclear Industry thatasustainedhighstandardofnuclearsafetyrequirestheapplicationoftheprincipleofcontinuousimprovementandthatextendingthescope of the stress tests to NPGNF provides an important opportunity to look for additional safetyenhancementsatthesesites.

Asnotedabove,thestresstestsrequirementshavebeenspecificallytargetedbyENSREGatNPPsandsomeof the requirements,whichare focussedon reactors,donotnecessarilyapply readily toother typesofnuclear installation. This is particularly so on siteswhere nuclear hazards, in terms of the potential forreleases of radioactivity, are at amuch lower level than onNPPs. TheNPGNF licensees andONR havefollowed thestructureandcontentsof thestress testsreportasdefinedbyENSREGas faraspossible inorder tokeepconsistencybetweenNPPandNPGNFstress tests.Theoriginalrequirementsstructurehashadtobeamendedslightlytoavoidfocusingonscenarioswhichhardlyapply,ordonotapply,toNPGNF.AlthoughtheNPPstresstestsprocessisnotalwaysappropriateforassessingNPGNFresilience,thesafetypurposeisidentical:restrictingradioactivereleasessofarasreasonablypracticable.

Incommonwith theearlierNPPstress tests, theNPGNFstress tests reportshavebeenpreparedby thelicenseesandsubmittedtoONRfor independentregulatoryreview.However,unlikeONRsNationalFinalReportforUKNPPs,theNPGNFstresstestsreportisapurelyUKinitiativeandwillthereforenotbesubjectto peer review by an ENSREG team. Nevertheless, the NPGNF stress tests have followed the ENSREGspecificationasfaraspossible,andONRhasreviewedthereportsusingthesameprinciplesandstandardsas for theONRsNational FinalReport forUKNPPs.Consequently it is judged thatany relevant furtherlearningresultingfromtheENSREGpeerreviewcanbetranslatedtoNPGNF.

ForNPGNFwithrelativelysmallnuclear inventories,ONRhas introducedaspecificsectiondedicatedtoamorelimitedtreatmentforthelowesthazardsites,inaccordancewiththeproportionalityprinciple.Thisisjudgedreasonableassuchsitesare incapableofgivingrisetosignificantoffsitedoses,even iftheworstwastohappenwithoutthebenefitofanyprotectionormitigationmeasures.

Conclusionsandfindings

ONR confirms in this report thatUK licensees have submitted stress tests reviews in linewith ENSREGspecification.DuetothenumberandthesizeoftheinstallationsatSellafield,thelicenseeSellafieldLtdhas,inagreementwithONR,focussed itsstresstestsreportonthe20main installationsonsite.FurtherworkonwiderresiliencechallengesisunderwayandisexpectedtobetransmittedtoONRduringthesummerof


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2012. It is likely that all Sellafield installationswillbe coveredby the improvements and theprovisionsalready identified or implemented onsite after completion of the stress tests. Nevertheless, ONRwillexaminetheworkonwiderresilienceissuesindetailtoensurethatanypotentialadditionalmeasuresareproperlyconsidered.AsfarasthelegacyfacilitiesatSellafieldareconcerned,RecommendationFR2ofHMChiefInspectorsreportremainsparamountwiththefocusbeingonhazardreduction.

Neitherthereviewsundertakenbythelicenseesforthestresstests,northeearliernationalreviews,haveindicatedany fundamentalweaknesses in thedefinitionofdesignbasiseventsor the safety systems towithstandthemforUKnuclearinstallations.ThiswasalsoaconclusionofHMChiefInspectorsfinalreport(Ref.2).

Thestresstestsprocessasappliedbylicenseeshasbeenrobustandchallengingforthedesignbasisevents.Forbeyonddesignbasisevents,theprocesshasalsobeenchallengingdue,inpart,tothenovelapproachprescribedbyENSREG.Furtherworkwillbeneededbysomelicenseestoachieveaconsistentstandardforanalysisofbeyonddesignbasisexternalhazardsandbeyonddesignbasissevereaccidentmanagement.Inaddition we are aware of relevant work that has already been carried out by licensees, but was notincludedintheirstresstestsreports.

The lessonstobe learnedpresented intheONRreportsandtheECstresstestsassessmentssharemanycommon themes. Through them both, the licensees have identified a significant number of potentialimprovementstoenhancetheirresilienceinpotentialemergencysituationsfollowingevents,orsequencesofeventsbeyondthetraditionaldesignbasis.Thepotentialimprovementsidentifiedalsoseektoenhancemarginassessmentmethodswith theaimofproviding furtherconfidence inthedesignandoperationoftheplants.There isalsopotential for improving the typeornumberof safetymeasureswhich, in turn,shouldincreasetheoveralldefenceindepth.

The listof further studies andpotential resilience enhancements,which are termedConsiderations, areprovidedinAnnexes2to5;typicalexamplesinclude:

Floodresilienceenhancements.

Sitepowerdistributionnetworkresilienceenhancements.

Provisionofimprovementstoemergencybackupequipment.Thisequipmentmayinclude:

Dieselgeneratortoprovidebackuptoemergencycentres.

Meansofsafelyaccessingthesiteintheeventofflooding.

Meansofmovingemergencysupportequipmentinaccidentconditions.

Emergencycommandandcontrolfacilitiesincludingcommunicationsequipment.

Emergencyresponse/recoveryequipment

FurthertotheConsiderationsidentifiedbythelicensees,ONRhasraisedanumberofStressTestsFindings(STF)which are detailed in the table below. Some of these findings reinforce or extend Considerationsidentifiedby the licenseeswhileothersareadditional to them. Itshouldalsobenoted that the findingsraisedinthisreportgenerallyrelatetomorespecificaspectsorelementsofthebroaderrecommendationsalready raisedbyHMChief InspectorofNuclear Installations.A tablemapping licenseesConsiderations,HMChiefInspectorsrecommendationsandONRsSTFsisincludedinthereporttoshowhowtheyrelatetooneanother(seeAnnex6).

Thereare15differentlicenseesandonepotentiallicenseeconsideredinthisreport.Fiveofthemoperatesites,whichONRhas judgedtobe lowerhazard,giventhenuclearmatter inventory,these licenseesare:ImperialCollegeofScienceTechnologyandMedicine,StudsvikLtd,LowLevelWasteRepositoryLtd(LLWR),ResearchSitesRestorationLtd(RSRL)andGEHealthcare(GEHC).Inaddition,therearenoONRstresstestsfindingsontheCapenhurstsiteoperatedbySellafieldLtd.


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Themajorityofthefindingsrequirethelicenseestoundertakesomefurtherreviewsfollowingstressteststhemes.ThenumberoffindingsraisedforeachNPGNFlicenseeisalsovariable.However,inbroadtermsitis fair to say that themajority of findings are aimed at severe accidentmanagement and the backupcapabilityforkeysystemsorfunctions.Therearealsoanumberoffindingsrecommendingthatbetter,ormore extensive, assessment of the seismic hazard, flooding and extreme weather events may beappropriate.

Toavoidanyconfusionwiththe19STFsalreadyraisedfortheNPPs(Ref.10),whicharenumberedSTF1toSTF19,thelistofSTFsbelowstartsatSTF20.Itcontains75STFs.Therelativelylargenumberoffindingsincomparison to ONRs National Stress Tests Final Report for UK NPPs is a reflection of the number oflicenseesinvolvedandthediversenatureofthefacilitiestheyoperate.Itisalsofairtosaythatthelevelofdetailinthestresstestsreportsvariesandthishashadsomeinfluenceonthenature,contentandnumberof STFs.Of the STFs identified in this report two are generic, 25 cover Sellafield Ltd, 33 cover the fivedefence licensees AtomicWeapons Establishment (AWE), RollsRoyceMarine Power Operations Ltd(RRMPOL), BAE SystemsMarine Ltd (BAESM), Devonport Royal Dockyard Ltd (DRDL) and Rosyth RoyalDockyardLtd(RRDL);sixarededicatedtoDounreaySiteRestorationLtd(DSRL),threetoSpringfieldsFuelLtd,twotothedefuelledreactorsofMagnoxLtd,twotoUrencoUKLtd,onetoResearchSiteRestorationLtd (RSRL)andone isaddressedtoEDFEnergyNNBGenerationCompanyLtd (NNBGenCo) inrelationtothepotentialfuturelicensedsiteatHinkleyPointC.

TheSTFsbeloware framed in the contextof continuous improvement,and the conclusionofHMChiefInspectorsreportstatingthatONRseesnoreasontocurtailtheactivitiesofnuclearinstallationsintheUKremainsvalid.

Table0:ONRsStressTestsFindings

FindingNo.

ONRsStressTestsFindings

STF20 SellafieldLtd,AWE,RRMPOL,BAESM,DRDL,RRDL,MagnoxLtdandNNBGenCoshouldprovideONRwiththedecisionmakingprocesstobeappliedtotheirConsiderationsalongwithareportwhichdescribesthesentencingofalltheirConsiderations.ThereportwillneedtodemonstratetoONRthattheconclusionsreachedareappropriate.

STF21 SellafieldLtdshouldconsiderfurtherandprovidemoredetailsonhowemergencyarrangementstodealwithasitewideextremeeventwouldanticipateandadapttochallengingcriticalityevents.

STF22 SellafieldLtdshouldestablishifthereisanythingreasonablypracticablethatcanbedonetoprovide/strengthentheprovisionofbasicplantinformation(e.g.inventorylevelandtemperature)during/followinganextremeeventonsiteaffectinghighhazard/highriskfacilities.

STF23 SellafieldLtdshouldtakenoteofNNPfindingSTF2[Ref.10]andparticipateinthereviewasnecessarywheretheseismicityoftheareaaffectingthesiteisunderconsideration.

STF24 SellafieldLtdshouldreviewtheinformationusedtoinformtheseismicdamageassessmentconclusionsinlightofmorerecentexperienceanddetailedanalysiscompletedforperiodicsafetyassessmentstoconfirmexpectedwithstandcapacityforfacilitieswithsignificantinventories.

STF25 SellafieldLtdshouldcompletefurtherworktoassesstheextentofseismicdamagetolocalinfrastructure.Thisworkshoulddemonstratetheextenttowhichlocalservicescanfunctionfollowingconnectionoftemporarypowersupply.

STF26 AWEshouldconsiderreassessingthenuclearsafetyimplicationsofconsequentialevents,suchaswateringress,multifacilityfiresandlossofemergencycontrolandcoordinationcentres,followingasignificantseismiceventtoestablishwhetherfurthermeasuresareneededtoreducetheassociatedrisks.


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FindingNo.


STF27 RRMPOLshouldconsiderreviewingwhetherthefailureofthefourbuildingsidentifiedinitssubmission,whensubjectedtoadesignbasisearthquake,couldunderminethehigherseismicwithstandoftheequipmentthosebuildingscontain.

STF28 RRMPOLshouldconsiderreviewingwhatimprovementscouldbemadetoimprovetheseismicwithstandofequipmentwithintheproductionfacilitythatcouldhaveanimpactonradiologicalrelease.

STF29 BAESMshouldconsiderreviewingwhetherthereareanyfurtheroptionsforminimisingthepotentialforphysicalimpactsduringaseismiceventonradioactivecomponentsduringconstructionactivities.

STF30 BAESMshouldconsiderreviewingtheseismicwithstandcapabilityofthedocksillsandtheirimpactforeventsexceedingthe1in100yearreturnperiod,whenthedockwallsarepredictedtohavefailed.

STF31 BAESMshouldconsidertheprovisionofahardenedrobustemergencycontrolcentreorproposeformalisedalternativearrangements.

STF32 DRDLshouldconsiderassessingthepossibleeffectsoffirefollowingaseismicevent.

STF33 SellafieldLtdshouldconsidertherangeofbeyonddesignbasisearthquakesthatcouldchallengecontainmenttodemonstratetheextentofrobustnessoffacilities.Thereviewcanbebasedonreasonedengineeringjudgementanddemonstrationofductileresponseratherthanrepeatedanalysis.

STF34 UrencoUKLtdshouldconsidertheimpactonresourcesrequiredtorespondtocombinationsofmoreextremeeventsthatmightdelayorpreventemergencyactions.Thisreviewshouldexaminetheeffectofconcurrentcriticalityonabilitytoaffectsaferescueofinjuredpersonnelandthevalidityofassumptionsoncapabilitytomitigateasevereaccidentpropagating.

STF35 BAESMshouldconsiderexpandingitsproposedassessmentoftheimpactofacredibletsunami,toconsidertheeffectsofanearthquakeexceedingthedesignbasisearthquakefortheplantsandconsequentfloodingexceedingthedesignbasisflood.

STF36 RRMPOLshouldconsiderassessingthechallengersfromincreasedseismicallyinduceddamageonsiteandoffsiteandthelimitationsthatimposesonexternalsupportandpossibleconsequencesofseismicallyinducedfire.

STF37 SellafieldLtdshouldcompletefurtherworktoidentifypotentialfailuremechanismsfollowingbeyonddesignbasisseismicevents,includingthepossibilityforsuddencollapseandcliffedgefailureofsafetyfunction.

STF38 SellafieldLtdshould,inlightofadvancesinrivermodellingmethodologies,climatechangeinformationandtheknownerosionoftheriverbed,reassesstheflowcapacityofthechanneloftheRiverCaldertobetterinformtheassessmentofriskofflood.

STF39 BAESMshouldconsiderassessingtherateofwaterlevelriseandflowrateoffloodwatersforthesitetodetermineifthereisanyerosionofsafetymarginsduringadynamicfloodevent.

STF40 DRDLshouldreviewitssafetycasestoconfirmthattheeffectofrapidfloodingofthedockfromafailureofthewatertightboundaryisconsidered.

STF41 AWEshouldconsiderreassessingthesitefloodmodeltodeterminethepotentialerosionofsafetymarginsresultingfromlossofthedrainagenetworks.

STF42 DSRLshoulddemonstratetoONRtherationalewithwhichithasconsideredthemobilityofwasteinventoriesinfloodingeventswhenprioritisingtheorderwithwhichhazardreductionactivitiesareplannedwithinitsdecommissioningstrategy.

STF43 AWEshouldconsiderassessingthenuclearsafetyimplicationsofconsequentialeventsincludingprogressivelossofstructures,systemsandcomponentsfollowinganextremefloodingeventtoestablishwhetherfurthermeasuresareneededtoreducetheassociatedrisks.


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FindingNo.


STF44 BAESMshouldconsiderprovidingfurthersubstantiationoftheclaimthatthereisa1.5mmarginofsafetybeyondthedesignbasisfloodevent.

STF45 RRMPOLshouldconsiderassessingaspectsofextremeweatherotherthansnowandwind,suchashighandlowtemperatureandhumidity,rainfallandlightning.

STF46 RRMPOLshouldconsiderreassessingthedesignbasisforextremeweatherevents.

STF47 MagnoxLtdshouldcarryoutareviewofthedesignbasisandmarginsavailableagainstexternalhazardsateachdecommissioningsitetoensureadequateprovisionsareinplacethroughoutthedecommissioningprocesscommensuratewiththeremainingradiologicalhazardpotential.

STF48 RRMPOLshouldconsiderreviewingtheutilisationfactorsandcriteriausedforassessingstructuralperformanceinextremeweather.

STF49 AWEshouldconsiderassessingthenuclearsafetyimplicationsofconsequentialeventsincludingprogressivelossofstructures,systemsandcomponentsfollowinganextremeweathereventtoestablishwhetherfurthermeasuresareneededtoreducetheassociatedrisks.

STF50 SellafieldLtdshouldcompleteareviewofthepossibleimpactofextremeweatherconditionsonservicenetworksandtemporaryserviceconnectionpointstoensuresecurityofsupplyandconfirmfunctionalityofconnectionpoints.

STF51 SellafieldLtdshouldundertakeregularloadforecastinginordertoidentifylikelyshortfallsintheprovisionsfornormalandbackupelectricalsupplyingoodtimetoplananddelivereffectiveremedialactionsandhenceavoidmaterialshortfallsoccurring.

STF52 SellafieldLtdshouldensurethatthelearningfromitsresiliencereviewregardingvitalsiteloadsisembeddedintofutureperiodicreviewsofsiteelectricalrequirementsandtakenintoconsiderationinthemanagementofchangeprocesswheneversiteelectricalloadsaretobemodified.

STF53 SellafieldLtdshouldcompleteitsreviewofresilience,includingtheneedforsuitableeventqualifiedmobiledieselalternatorconnectionpoints,andshouldundertakeimprovementswherethesewouldfacilitatethereconnectionofsuppliestoidentifiedessentialequipment.

STF54 SellafieldLtdshouldcontinuetoidentifyandaddresspotentialvulnerabilitiesintheprovisionofelectricalsuppliestosystemsthatmaynothaveanexplicitnuclearsafetyclaiminfacilitysafetycasesbutwhoselosscouldseverelyhindersiteemergencyarrangementfollowingasevereevent.

STF55 DSRLshouldidentifyandaddresspotentialvulnerabilitiesintheprovisionofelectricalsuppliestosystemsthatmaynothaveanexplicitnuclearsafetyclaiminfacilitysafetycasesbutwhoselosscouldseverelyhindersiteemergencyarrangementfollowingasevereevent.

STF56 RRMPOLshouldconsiderreviewingitsstrategyfordemonstratingthecontinuingsafetyoftheplantpostincident,includingaconsiderationofpowerrequirementsforinstrumentation(e.g.criticalitydetectionsystems).

STF57 BAESMshouldconsiderwhetherfurthermeasuresarenecessarythatmayimprovetheavailabilityofelectricalpowersuppliesonsiteunderafullrangeoffaultscenarios.Thisshouldincludeareviewoftheadequacyofbackupelectricalsuppliesonsitethatwouldsupportthemanagementandoperationofanemergencyincident.

STF58 NNBGenCoshouldconsiderfurthertheabilityofthesitetorespondtothepartialorcompletelossofelectricalsuppliesandtheautonomytimesofsystemswithoutoffsitesupport.

STF59 SellafieldLtdshouldexplorethepracticalityandrequirementsofpumpingwaterfromtheseaandotherwatersourcessuchaslocalriverstowhereitmightbeutilised,andestablishifthiscouldindeedbedoneinextremiswiththesystemscurrentlyavailableonsite.


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FindingNo.


STF60 BAESMshouldconsiderreviewingthearrangementsthatensuresuitablesystemsarealwaysavailablecommensuratewithexpectedlevelsofdecayheat,andthatresources(fuelandwater)areavailableonboardandonshoreforreplenishmentwherenecessary.

STF61 DSRLshouldreviewtheeffectivenessofexistingonsitecommunicationarrangementswhichhavenotbeensubjecttofullevaluationduringthestresstestsprocess.

STF62 DSRLshouldcoordinatewiththeHighlandCounciltoreviewtheadequacyofexistinglocalreceptioncentresdetailedinitsoffsiteplan.

STF63 SpringfieldsFuelsLtdshouldevaluatereasonablypracticablestructuralimprovementstoitsdesignatedemergencycontrolcentre,takingintoaccountreasonablyforeseeableaccidentsthatmayhinderitsavailability.

STF64 SellafieldLtdshouldreviewthesevereaccidentguidelinestakingintoaccountimprovementstotheunderstandingofsevereaccidentprogression,phenomenaandtheequipmentavailabletomitigatesevereaccidents(inlinewithSTF16).

STF65 SellafieldLtdshoulddevelopandrehearseemergencyexercisescenarioscoveringbeyonddesignbasiseventsandsevereaccidentconditions.

STF66 SellafieldLtdshouldextenditsreviewoftheresilienceofthebackupsuppliesinsupportofthesitedatanetworkandassesstheresilienceofthesitecommunicationsystemtodesignbasisnaturaleventsandsevereaccidents.

STF67 SellafieldLtdshouldextenditsreviewofavailabilityofexternalresourceandreviewitsinplantcommunicationsystemsusedbysitefireandrescueteams(e.g.radios)toensurethereiscompatibilitywithequipmentusedbyexternalemergencyservices,especiallyatidentifiedradioshieldedareas.

STF68 SellafieldLtdshouldextenditsprogrammefordevelopmentofsevereaccidentmanagementstrategiestoitsstrategicnonnuclearsupportfacilitiestoensureadequateinformationandsupportcanbeprovidedtotheSellafieldemergencycontrolcentreintheeventofasevereaccident.

STF69 GiventheextentoftheSellafieldsiteandtheneedforcountermeasuresonthesiteintheeventofanaccident,SellafieldLtdshouldemployallreasonablypracticablemeanstoensureweatherforecastinformationcanbemadeavailabletoitsemergencycontrolcentre/strategicmanagementcentresothattimelyadvicecanbeprovidedonsite.

STF70 SellafieldLtdshouldtakecognisanceofSTF14[Ref.10],andconfirmtheextenttowhichresilienceenhancementsaretobemadetoexistingequipmentandsystemsthatarecurrentlyinstalledacrossthesite.Informationshouldbeprovidedontheequipmentandsystemsthatmaybeaffectedandthenatureoftheresilienceenhancement,includingthemobilebackupequipment.

STF71 SellafieldLtdshouldfurtherassesstheavailabilityandoperabilityofelectronicpersonaldosimetersinaprolongedstationblackout,inconditionsassociatedwithdesignbasisnaturaleventsandinsevereaccidents.

STF72 SellafieldLtdshoulddevelopastrategyforincorporatingallreasonablypracticablemeasuresidentifiedaspartofitsresilienceevaluationprocessinitsprogrammeforenhancingitsemergencyresponsecapability.

STF73 DSRLshouldextenditsproposedreviewofresiliencetolonglivedeventstakingduecognisanceoftheimpactofwidespread(offsite)disruptiontolocalandnationalinfrastructure,continuingtocoordinatewithNuclearEmergencyArrangementsForum.

STF74 DSRLshouldfurtherconsiderhowthesitemightobtaintechnicalsupportfromthewiderindustryintheeventofasevereaccident.


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FindingNo.


STF75 Alldefencelicensees(AWE,RRMPOL,BAESM,DRDLandRRDL)shouldconsidertheapproachtakenbyseveralcivilianlicenseesofusingbeyonddesignbasiscontainersthatcontainarangeofequipmentandmaterialsthatcouldbebeneficialwhenrespondingtoabeyonddesignbasisaccident.ThisfindingisofasimilarnaturetothatraisedintheONRNationalStressTestsFinalReportforUKNPPs(STF15).

STF76 AWEshouldreconsidertheprovisionofsuitablecontingenciesinitsemergencyresponsetoextremeexternaleventsifaggravatingfactors,whichmayimpedeaccidentmanagement,arerealised.Thesefactorsincludeimpairedroadaccesstoboththesitesthemselvesandtoindividualfacilitiesonsite,lossofavailabilityofcoordinationandcontrolcentresandlossofcommunication.

STF77 AWEshouldconsidercollatingrequirementsplacedonthesitewideinfrastructureandemergencyarrangementsbyindividualfacilitysafetycasesandconsiderthedemandsthatmaybeplacedontheorganisation,infrastructureandresourcesshouldaresponseberequiredattwoormorefacilitiessimultaneously,orwithinthesameincident.AWEshouldconsideridentifyingotherfactorsthatmayimpairtheemergencyresponseanddevelopsuitablecontingenciestoensurethatthelogisticsoftheemergencyresponsearerobust.

STF78 AWEshouldconsiderreviewingtheonsiteandoffsitedoseconsequencesofbeingunabletofollowitsstrategyofmakingsafeandevacuatinghighhazardfacilitiesinresponsetoextremeexternalevents.

STF79 RRMPOLshouldconsiderreviewingthestresstestsrequirementswhenthemanufacturingsiteregenerationprojectandmodificationstotheNeptunefacilityaresufficientlymature.

STF80 RRMPOLshouldconsiderreviewingtheresilienceofBronzeCommandstoseismiceventsorproposealternativearrangements.

STF81 RRMPOLshouldconsiderreviewingitsemergencyarrangementsforcoincidentevents.

STF82 DRDLshouldconsiderenhancingthewithstandoftheforwardcommandpoststofloodingandtheDevonportaccidentcontrolcentretoseismiceventsorproposeformalisedalternativearrangements.

STF83 MagnoxLtdshouldreview,updateandissuerevisedsevereaccidentguidelinesinthelightofchanginghazardatdecommissioningsites;theguidelinesshouldincludehumanperformance/welfareissuesandavailabilityofequipmentlocatedinbeyonddesignbasiscontainers.

STF84 UrencoUKLtdshouldreviewitsexistingemergencyplanstoensurethat,inrelationtotheresponsetoacriticalityaccident,theplansincorporatefurtherdetailstosupporttheprincipleofextendibilityforoffsiteresponseandcontrolofreactivitythroughtheuseofneutronpoisonsifpracticable.

STF85 SpringfieldsFuelsLtdshouldconsiderwhetherthesecuringofneutronpoisonsisareasonablypracticableimprovementtoemergencypreparednessfollowingarepeatingcriticalityincident.

STF86 SellafieldLtdshouldundertakesafetymarginanalysisinordertodeterminerelativewithstandofcontainmentstructurestoabeyonddesignbasisoverpressure.

STF87 SellafieldLtdshouldconsider,inmoredetail,theconsequencesoffirecoincidentwithcriticalityandthecapabilityofSellafieldsitetorespondtotheseevents.

STF88 SpringfieldsFuelsLtdshoulddemonstratehowitsonsiteandoffsiteplanscaterforwidespreaddispersionofuranicmaterial(inoxideformanduraniumhexafluoride)predicatedonconcurrentseismic/hydrogendetonationevents

STF89 DRDLshouldconsiderreviewingitscapabilityforsevereaccidentmanagementincasesofsimultaneouscoredamageaccidents.

STF90 AWEshouldconsiderreviewingthethreatposedtocontainmentsystemsfromfirehazardsandthepotentialdoseconsequencesforonsiteandoffsiteriskgroups.AWEshouldconsider,withinitsreview,thepotentialdoseconsequencesofanextremeeventleadingtoalossofcontainmentandaconsequentialfire.Inlightoftheassessedconsequencesforworkersandthepublic,AWEshouldconsideranyfurthermitigation,inadditiontothosemeasurescurrentlyinplace.


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FindingNo.


STF91 DRDLshouldconsiderreviewingitsresponsesrequiredintheeventofalossofshieldingofstoredfuel.

STF92 DRDLshouldconsiderreviewingthenuclearfuelandsourcemovementsonsitetodemonstratethecomprehensivenessoftheemergencyresponsemeasuresavailable.

STF93 RSRLshouldreviewtheavailabilityandcapabilitytodeploydieselandgeneratorsinordertosustainventilationofhydrogengeneratingintermediateandlowlevelradioactivewasteonthesite;thismaybeadequatelyaddressedthroughasuitabledeterministicargumentifonecanbemaderegardingminimalgenerationrateswhenintermediateandlowlevelwasteisinmatrixform.

STF94 ReportsontheprogressmadeinaddressingtheconclusionsofthelicenseesConsiderationsandtheONRfindingsshouldbemadeavailabletoONRonthesametimescaleasthatforHMChiefInspectorsrecommendations(June2012).Theseshouldincludethestatusofplansanddetailsofimprovementsthathavebeenimplemented.

Wayforward

ONR anticipates that the stress tests process will finish when the improved processes, plant andprocedures, resulting from theConsiderationsand stress tests findings,move into the licenseesnormalproceduresforchangeandreviewofsafetycases in linewithrelevantnuclearsite licenceconditions.AnImplementation Report, to be published by ONR in autumn 2012, will confirm progress towards thistransition and STF94 above requires the licensees to provide reports on the status of work onConsiderationsandstresstestsfindingsinJune2012.


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Contents0 INTRODUCTION........................................................................................................................................ 1

0.1 Background ...................................................................................................................................... 1 0.1.1 TheFukushimaEvents...................................................................................................................... 1 0.1.2 UKResponse .................................................................................................................................... 2 0.1.3 EuropeanCouncilResponse ............................................................................................................. 2 0.1.4 OtherInternationalResponses ........................................................................................................ 3

0.2 ENSREGRequirements ..................................................................................................................... 3 0.2.1 InitiatingEvents ............................................................................................................................... 4 0.2.2 LossofSafetyFunction .................................................................................................................... 4 0.2.3 SevereAccidentManagement ......................................................................................................... 5

0.3 RelevantAspectsofUKRegulatoryRegime..................................................................................... 5 0.3.1 LegalFramework ............................................................................................................................. 5 0.3.2 Licensing .......................................................................................................................................... 6 0.3.3 DesignBasis ..................................................................................................................................... 6 0.3.4 ExternalHazards.............................................................................................................................. 6 0.3.5 FaultAnalysis ................................................................................................................................... 7 0.3.6 SevereAccidentManagement ......................................................................................................... 7 0.3.7 PeriodicSafetyReview..................................................................................................................... 7 0.3.8 RadiationEmergencyPreparednessandPublicInformationRegulations....................................... 8 0.3.9 ContinuousImprovement ................................................................................................................ 8

0.4 LicenseesCoveredbytheScopeofNPGNFStressTests.................................................................. 8 0.4.1 DefenceLicensees ............................................................................................................................ 8 0.4.2 EDFEnergyNNBGenerationCompanyLtd(NNBGenCo)................................................................ 9

0.5 ProcessforStressTestsActivities .................................................................................................. 10 0.5.1 OverviewandTimeline .................................................................................................................. 10 0.5.2 LicenseeProcessesforProducingStressTestsReports.................................................................. 10 0.5.3 ONRsAssessmentProcess............................................................................................................. 11 0.5.4 ONRsReportingProcess................................................................................................................ 11

1 GENERALDATAABOUTTHESITESANDNPGNF .................................................................................... 13 1.1 BriefDescriptionoftheSiteCharacteristics .................................................................................. 14

1.1.1 MainCharacteristicsofUKNPGNF ................................................................................................ 19 1.1.2 DescriptionoftheSystemsforDeliveryofMainSafetyFunctions................................................. 34

1.2 SignificantDifferencesBetweenUnits........................................................................................... 46 1.3 UseofPSAasPartoftheSafetyAssessment................................................................................. 48 1.4 ONRsConclusion ........................................................................................................................... 51

2 EARTHQUAKES ....................................................................................................................................... 57 2.1 DesignBasis.................................................................................................................................... 57

2.1.1 EarthquakeAgainstWhichthePlantsAreDesigned ..................................................................... 57 2.1.2 ProvisionstoProtectthePlantsAgainsttheDesignBasisEarthquake.......................................... 65 2.1.3 PlantsCompliancewithTheirCurrentLicensingBasis.................................................................. 77

2.2 EvaluationofSafetyMargins ......................................................................................................... 80


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2.2.1 RangeofEarthquakeLeadingtoSevereNuclearMatterDamage................................................ 80 2.2.2 RangeofEarthquakeLeadingtoLossofContainmentIntegrity ................................................... 84 2.2.3 EarthquakeExceedingtheDesignBasisEarthquakeforthePlantsandConsequentFlooding

ExceedingDesignBasisFlood ........................................................................................................ 88 2.2.4 MeasuresWhichCanBeEnvisagedtoIncreaseRobustnessofthePlantsAgainstEarthquakes ..92

2.3 ONRsConclusion ........................................................................................................................... 95 3 FLOODING.............................................................................................................................................. 99

3.1 DesignBasis.................................................................................................................................... 99 3.1.1 FloodingAgainstWhichthePlantsAreDesigned.......................................................................... 99 3.1.2 ProvisionstoProtectthePlantsAgainsttheDesignBasisFlood ................................................. 110 3.1.3 PlantsCompliancewithTheirCurrentLicensingBasis................................................................ 119

3.2 EvaluationofSafetyMargins ....................................................................................................... 124 3.2.1 EstimationofSafetyMarginsAgainstFlooding........................................................................... 124 3.2.2 MeasuresWhichCanBeEnvisagedtoIncreaseRobustnessofthePlantsAgainstFlooding....... 127 3.2.3 ONRsAssessmentofEvaluationofSafetyMargins .................................................................... 130

3.3 ONRsConclusion ......................................................................................................................... 133 4 EXTREMEWEATHERCONDITIONS....................................................................................................... 137

4.1 DesignBasis.................................................................................................................................. 137 4.1.1 ReassessmentofWeatherConditionsUsedasDesignBasis ....................................................... 137

4.2 EvaluationofSafetyMargins ....................................................................................................... 145 4.2.1 EstimationofSafetyMarginaboveDesignBasisEventsAgainstExtremeWeatherConditions .145 4.2.2 MeasuresWhichCanBeEnvisagedtoIncreaseRobustnessofthePlantsAgainstExtreme

WeatherConditions ..................................................................................................................... 151 4.3 ONRsConclusion ......................................................................................................................... 153

5 LOSSOFELECTRICALPOWERANDLOSSOFULTIMATEHEATSINK..................................................... 156 5.1 LossofElectricalPower................................................................................................................ 156

5.1.1 LossofOffsitePower .................................................................................................................. 156 5.1.2 LossofOffsitePowerandLossoftheOrdinaryBackupACPowerSource ................................ 161 5.1.3 LossofOffsitePowerandLossoftheOrdinaryBackupACPowerSources,andLossof

PermanentlyInstalledDiverseBackupACPowerSources.......................................................... 163 5.1.4 LicenseeConclusionontheAdequacyofProtectionAgainstLossofElectricalPower ................ 165 5.1.5 MeasuresWhichCanBeEnvisagedtoIncreaseRobustnessofthePlantsinCaseofLossof

ElectricalPower ........................................................................................................................... 167 5.1.6 ONRsAssessmentofLossofElectricalSupplies .......................................................................... 169

5.2 LossoftheDecayHeatRemovalCapability/UltimateHeatSink ............................................... 174 SELLAFIELDLTDSELLAFIELDANDWINDSCALE........................................................................................... 174

5.2.1 DesignProvisionstoPreventtheLossofthePrimaryUltimateHeatSink,suchasAlternativeInletsforSeawaterorSystemstoProtectMainWaterInletfromBlocking.......................................... 174

5.2.2 LossofthePrimaryUltimateHeatSink ....................................................................................... 176 5.2.3 LossofthePrimaryUltimateHeatSinkandtheAlternateHeatSink .......................................... 178 5.2.4 ConclusionontheAdequacyofProtectionAgainstLossofUltimateHeatSink .......................... 179 5.2.5 MeasuresWhichCanBeEnvisagedtoIncreaseRobustnessofthePlantsinCaseofLossof

UltimateHeatSink....................................................................................................................... 180 5.2.6 ONRsAssessmentofLossoftheDecayHeatRemovalCapability/UltimateHeatSink............. 182


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5.3 LossofthePrimaryUltimateHeatSink,CombinedwithStationBlackout ................................. 184 5.3.1 TimeofAutonomyoftheSiteBeforeLossofNormalCoolingConditionoftheNuclearMatters185 5.3.2 ExternalActionsForeseentoPreventNuclearContainmentDegradation .................................. 186 5.3.3 MeasuresWhichCanBeEnvisagedtoIncreaseRobustnessofthePlantsinCaseofLossof

PrimaryUltimateHeatSink,CombinedwithStationBlackout .................................................... 187 5.3.4 ONRsAssessmentofLossofPrimaryUltimateHeatSinkCombinedwithStationBlackout....... 188

5.4 ONRsConclusion ......................................................................................................................... 189 6 SEVEREACCIDENTMANAGEMENT...................................................................................................... 192

6.1 OrganisationandArrangementsoftheLicenseetoManageAccidents...................................... 192 6.1.1 OrganisationoftheLicenseetoManagetheAccident ................................................................ 192 6.1.2 PossibilitytoUseExistingEquipment .......................................................................................... 199 6.1.3 EvaluationofFactorsThatMayImpedeAccidentManagementandRespectiveContingencies 205 6.1.4 ConclusionontheAdequacyofOrganisationalIssuesforAccidentManagement...................... 211 6.1.5 MeasuresWhichCanBeEnvisagedtoEnhanceAccidentManagementCapabilities ................. 213 6.1.6 ONRsAssessmentoftheOrganisationandArrangementsoftheLicenseetoManageAccidents

..................................................................................................................................................... 215 6.2 AccidentManagementMeasuresinPlaceattheVariousStagesofaScenarioofLossofthe

CoolingFunction .......................................................................................................................... 224 6.2.1 BeforeOccurrenceofFirstContainmentBarrierDamage ........................................................... 225 6.2.2 AfterOccurrenceofFirstContainmentBarrierDamage.............................................................. 226 6.2.3 AfterFailureoftheSecondContainmentBarrier......................................................................... 227 6.2.4 ONRsAssessmentofAccidentManagementMeasuresinPlaceattheVariousStagesofa

ScenarioofLossoftheCoolingFunction ..................................................................................... 228 6.3 MaintainingtheContainmentIntegrityafterOccurrenceofSignificantNuclearMatterDamage

(uptoNuclearMeltdown)............................................................................................................ 229 6.3.1 EliminationofNuclearMeltdowninHighPressure ..................................................................... 229 6.3.2 ManagementofExplosiveRisksInsidetheContainment ............................................................ 230 6.3.3 PreventionofOverpressureoftheContainment ......................................................................... 232 6.3.4 PreventionofReCriticality .......................................................................................................... 234 6.3.5 PreventionofBasematMeltThrough.......................................................................................... 235 6.3.6 NeedforandSupplyofElectricalACandDCPowerandCompressedAirtoEquipmentUsedfor

ProtectingContainmentIntegrity ................................................................................................ 236 6.3.7 MeasuringandControlInstrumentationNeededforProtectingContainmentIntegrity............. 237 6.3.8 CapabilityforSevereAccidentManagementinCaseofSimultaneousNuclearMeltdown

AccidentsatDifferentUnitsontheSameSite ............................................................................. 238 6.3.9 ConclusionontheAdequacyofSevereAccidentManagementSystemsforProtectionof

ContainmentIntegrity.................................................................................................................. 239 6.3.10 MeasuresWhichCanBeEnvisagedtoEnhanceCapabilitytoMaintainContainmentIntegrity

afterOccurrenceofSevereNuclearMattersDamage................................................................. 240 6.3.11 ONRsAssessmentofMaintainingtheContainmentIntegrityafterOccurrenceofSignificant

NuclearMatterDamage(uptoNuclearMeltdown).................................................................... 242 6.4 AccidentManagementMeasurestoRestricttheRadioactiveReleases ..................................... 245

6.4.1 RadioactiveReleasesafterLossofContainmentIntegrity........................................................... 245 6.4.2 AccidentManagementafterUncoveringoftheTopofNuclearMattersintheStorageFacility 247 6.4.3 ConclusionontheAdequacyofMeasurestoRestricttheRadioactiveReleases ......................... 248


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6.4.4 ONRsAssessmentofAccidentManagementMeasurestoRestricttheRadioactiveReleases ... 250 6.5 ONRsConclusion ......................................................................................................................... 253

7 ONRASSESSMENTOFLOWESTHAZARDSITESSTRESSTESTS............................................................. 258 7.1 ONRGeneralAssessmentofLowhazardNPGNFSites................................................................ 258 7.2 ONRSitespecificAssessments .................................................................................................... 261 7.3 ONRsOverallConclusionoftheStressTestsforLowhazardNPGNFSites ................................ 266

8 GENERALCONCLUSION ....................................................................................................................... 267 8.1 KeyProvisionsEnhancingRobustness ......................................................................................... 267 8.2 SafetyIssues................................................................................................................................. 268 8.3 PotentialSafetyImprovementsandFurtherWorkForecasted................................................... 268

ANNEX1: CHIEFNUCLEARINSPECTORSCONCLUSIONSANDRECOMMENDATIONS................... 270 ANNEX2: SELLAFIELDLTDCONSIDERATIONS................................................................................ 281 ANNEX3: DEFENCELICENSEESSTRESSTESTSCONSIDERATIONS.................................................. 284 ANNEX4: MAGNOXLTDSTRESSTESTSCONSIDERATIONS............................................................ 295 ANNEX5: NNBGENCOSTRESSTESTSCONSIDERATIONS .............................................................. 296 ANNEX6: OVERALLSUMMARYTABLEOFRECOMMENDATIONSORACTIONSINTHEUK ........... 298 9 REFERENCES......................................................................................................................................... 300 10 GLOSSARYANDABBREVIATIONS......................................................................................................... 303 11 CONTACTS............................................................................................................................................ 309


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0 INTRODUCTION1 This reportpresents theUK reporton the implementationof thestress tests toUKnonpower

generatingnuclearfacilities,alsodesignatedasNPGNFherein.

2 ThestresstestsaredefinedasatargetedreassessmentoftherelevantdesignbasesandsafetymarginsofNPPsinthelightoftheeventswhichoccurredatFukushima:extremenaturaleventschallenging the plant safety functions and leading to a severe accident. The stress testsrequirements have been set by the European Nuclear Safety Regulators Group (ENSREG)membersforNPPs.

3 Given that the European Council (EC) stress tests only focus onNPPs,HM Chief Inspector ofNuclear Installations decided to extend the stress tests process to all other licensed nuclearinstallationswithintheUK.

4 UKNPGNFlicenseeshavebeenadvisedbytheOfficeforNuclearRegulation(ONR)toundertakethestresstestsfollowingthespecificationsandguidelinesprovidedbyENSREGasappropriatetotheirfacilities.ThisreportdetailsthestresstestsasappliedtoUKNPGNF.

5 AlloftheUKlicenseeshaveundertakenprogrammesofworktocompleteallaspectsofthestresstestsandhaveprovidedcontributionstotheUKfinalreportwithintherequestedtimescales.Inordertofulfilthescopeofthestresstestsinameaningfulway,thelicenseesreportsnecessarilyinclude sensitive information regarding the systems necessary to ensure safety of the facility.ONRhashadfullandunfetteredaccesstoallofthisinformation.ONRandthelicenseeshavetobalancetherequirementtoprotectsensitiveinformationwiththerequirementtobeasopenandtransparentaspossible.Linkstopublished,summaryversions,ofalllicenseecontributionswillbeavailableontheONRwebsite.

0.1 Background6 AlloftheUKnuclearsitelicenseeshaveprocessestoassimilate,reviewanddisseminatelessons

learntfromsignificantevents,both intheUKandoverseas.Thesearrangementsarepartofthecontinuous improvement and operational experience (OPEX) feedback processes which arerequiredbyLicenceConditions(LC)imposedonalllicensees.

7 Themagnitudeandscaleof theeventsatFukushimaaresuch thatall the licensees respondedswiftlyandproactivelytoreviewsafetyattheirsites.Inaddition,theyhavebeenfullysupportiveandengaged inthewiderUKnuclear industryresponsesand international lessonsto learnfromtheseevents.

0.1.1 TheFukushimaEvents8 On11March2011 Japan suffered itsworst recordedearthquake,knownas theTohukuevent.

The epicentrewas 110miles east north east from the FukushimaDaiichi (Fukushima1) site.ReactorUnits1,2and3onthissitewereoperatingatpowerbeforetheeventandondetectionof the earthquake, shut down safely. Offsite power was lost and initially emergency dieselgenerator (EDG)powerwasused toprovideessentialposttripcooling.Less thananhouraftershutdown a massive tsunami from the earthquake inundated the site and destroyed the



capabilityfornearlyall*onsitegenerationofalternatingcurrent(AC)electricalpowerandlossofheatsinks.Sometimelater,alternativebackupcoolingwaslost.Withthelossofcoolingsystems,ReactorUnits 1 to 3 overheated. The overheated zirconium cladding reactedwithwater andsteam, generating hydrogenwhich resulted in several explosions causing damage to buildingstructures.Major releases of radioactivity occurred, initially to the atmosphere but later byleakagetosea.Theoperatorstruggledtorestorefullcontrol.

9 Thiswasamajornuclearaccident,ratedatanInternationalNuclearandRadiologicalEventScale(INES)level7(thehighestlevel).TheJapaneseauthoritiesinstigatedanevacuationzone,initially3kmbutlaterextendedto20km,anda30kmshelteringzoneandothercountermeasures.

0.1.2 UKResponse10 InresponsetotheFukushimaaccident,theUKopenedtheCabinetOfficeBriefingRoom(COBR).

The Government Chief Scientific Advisor chaired a Scientific Advisory Group for Emergencies(SAGE).HMChiefInspectorofNuclearInstallationsprovidedsignificantinputstobothCOBRandSAGE.TheRedgraveCourtIncidentSuiteinBootlewasstaffedbyONRfromearlyintheaccidentandforovertwoweeks itactedasasourceofexpertregulatoryanalysis,adviceandbriefingtocentralgovernmentdepartmentsandSAGE.

11 On14March,theSecretaryofStateforEnergyandClimateChangerequestedHMChiefInspectorofNuclear Installations to examine the circumstances of the Fukushima accident to seewhatlessonscouldbelearntfortheUKnuclearindustry.ONRsetupadedicatedprojectteamcoveringaspectsoftheFukushimaaccidentthatare likelytobe importantforlearning lessons.HMChiefInspector of Nuclear Installations also set up a Technical Advisory Panel (TAP) of externalindependentexpertstoadvisehimduringthiswork.

12 HM Chief Inspector of Nuclear Installations published his interim report on the events atFukushimaandtheimplicationsfortheUKnuclearindustryon18May2011(Ref.1).Thisreportcontained11conclusionsand26recommendations.HMChief InspectorofNuclear Installationspublishedhis final reporton11October2011 (Ref.2).This reportbuilton the findingsof theinterim report and added a further six conclusions and 12 recommendations. All of theconclusionsandrecommendationsfromboththesereportsarelistedinAnnex1.

13 HMChief InspectorofNuclear Installationsextended thestress tests requiredby theEC forallEuropeanNPPssee0.1.3belowtoincludeallUKlicensednuclearinstallations.

0.1.3 EuropeanCouncilResponse14 On24and25March2011,theEuropeanCouncildeclared,inrelationtocivilNPP,thatthesafety

ofallEUnuclearplantsshouldbereviewed,onthebasisofacomprehensiveandtransparentriskassessment (stress tests). European Nuclear Safety Regulators Group (ENSREG) and theEuropeanCommissionare invited todevelop,as soonaspossible, the scope andmodalitiesofthesetests inacoordinatedframework, in lightofthe lessons learntfromtheaccident inJapanandwith the full involvementofmember states,making fulluseofavailableexpertise (notablyfrom theWesternEuropeanNuclearRegulatorsAssociation (WENRA).Theassessmentswillbeconductedby independentnationalauthoritiesandthroughpeerreview;theiroutcomeandany

*One emergency aircooleddiesel generator remainedoperationalbut thisonly served reactor6, and eventuallyreactor5.



necessary subsequentmeasures thatwill be taken should be sharedwith the Commission andwithinENSREGandshouldbemadepublic.TheECwillassess initialfindingsbytheendof2011,onthebasisofareportfromtheCommission.TheEuropeanCommission istopresent itsfinalreporttotheECinJune2012.

15 ENSREGmembersagreedonthe initial independentregulatorytechnicaldefinitionofthestresstests andhow it should be applied toNPPs across Europe at theirplenarymeetingon 1213May2011. This was based on detailed work byWENRA. The final version of EC stress testsrequirementsonlyretainedNPPs.

0.1.4 OtherInternationalResponses16 HM Chief Inspector ofNuclear Installations led an International Atomic Energy Agency (IAEA)

highlevel teamof internationalnuclearexperts ina factfindingmission to Japan inMay2011andreportedbacktoaministerialconferenceoftheIAEAinJune2011.Areportonthemission(Ref.3)waspublishedshortlyafterwards.AcrucialinitialfindingofthemissionteamwasthatthetsunamiriskforseveralsitesinJapanhadbeenunderestimated.Italsoconcludedthatregulatorysystems should ensure that there are adequate arrangements for addressing extreme events,includingperiodicreviewofthosearrangements.TheECstresstestsarepartofthisprocess.TheIAEA has developed an action plan,which aims towiden the scope for lessons learned to allmemberstates.TheplanwasendorsedbytheIAEAatitsgeneralconferenceinSeptember2011.

17 The Japanese government has provided two reports on the accident to the IAEA: to theministerialconference,publishedinJune2011(Ref.4),andtothegeneralconference,publishedinSeptember2011(Ref.5).

18 An extraordinary reviewmeeting of the Convention on Nuclear Safety to review contractingpartiesprogressagainsttheactionplanwillbeheldinAugust2012.

19 TheUK has contributed to a significant number of other internationalmeetings and bilateraldiscussions relating to the Fukushima accident since March 2011, and this is expected tocontinue.ONRs staff, ledbyHMChief InspectorofNuclear Installations,playanactive role inthesemeetings.

0.2 ENSREGRequirements20 TheENSREGrequirements(Ref.6)areincludedinAnnex1oftheONRprogressreport(Ref.7).

21 ENSREGnotesthatlicenseeshavetheprimeresponsibilityforsafety,sotheyshouldperformtheassessmentsandtheregulatorybodyshouldindependentlyreviewthem.

22 The national regulatory bodies have been encouraged to take due account of the need foropennessandtransparencyandtomaketheirreportsavailabletothepublicwithintheboundsofsecurityand internationalobligations.ThisprincipleaccordswellwithONRsexistingopennessandtransparencyobjectives.ENSREGalsonotesthatitsreportsfromthepeerreviewprocessonNPPswillbemadepublic.

23 Asstatedpreviously,ENSREGrequirementshavebeendefinedforNPPsonlyanddonotincludeother nuclear installations. Hence, the structure and the technical rationale of theserequirementsarespecific tonuclear reactorsandassociated facilities (spent fuelponds).Someaspects of the stress tests requirements might therefore not apply to every NPGNF in astraightforwardmanner.



0.2.1 InitiatingEvents24 Theinitiatingeventsrequiredforreviewunderthestresstestsareearthquakes,floodingandbad

weather.Ineachcasethereviewconsidersthesizeandfrequencyofthedesignbasiseventandhow itwasdeveloped, alongwith a reviewofhow structures, systems and components (SSC)weredesignedorqualifiedtoresistthedesignbasisevent(s).

25 IntheUK,thelicenseesreviewedcompliancewiththeirsafetycasesinthefirstfewdaysaftertheFukushima event following a request fromONR.ONRmonitored thework undertaken by thelicensees.Thefindingsweregenerallypositive,althoughsomeminorissueswereidentified;thesewerequicklyresolvedbythelicensees.

26 The initiating event review for the stress tests must also consider how the safety marginsevaluationforeachSSCwascompletedandwhatconsequentialeffectsshouldbeconsidered.Theevaluation of safety margins includes a requirement for licensees to consider whatimprovements,ifany,couldbeappliedtoimprovemarginsandtoremoveorreducefurthertheprobabilityofcliffedgeeffects.

0.2.2 LossofSafetyFunction27 Thereare three connectedkey safety functions to servenuclear safetyatallnuclear facilities:

containment,controlandcooling.Controlcanbeofnuclearorchemicalreactionsandalongwithadequatecoolingensuresthatcontainment isnotbreached.Containmentcanbeofradioactivegases,aerosol,particulates,liquidsorsolidsandincludesshieldingtocontaindirectradiation.

28 Twokey lossofsafetyfunction fault sequencesmustbe reviewedduring the stress tests,bothseparatelyandincombination.Theseare:

Lossofelectricalpower.

Lossofultimateheatsink.

29 Theseevents,whichcouldleadtoalossofnuclearsafetyfunction,suchascooling,couldbeasaresultofseismicactivityorflooding,butotherexternalorinternalhazards,orfaultscouldalsobethe initiatorofthesesequences.This isrecognised inthetextoftheENSREGrequirementsandhas been considered by the licensees, where applicable. Thismeans that the impact of anyfindingswillhaveabroaderapplicationthanjustseismicactivity,floodingorextremeweather.

30 For lossofelectricalpower,progressive lossofsupplies isconsidered.Thisstartswitha lossofoffsite power (LOOP) this is always considered as a fault scenario in UK design basis andresilience isprovidedby a rangeofonsitepower generation and support facilities.Themoreseveresequencealsoconsidered forthestresstests isthe lossofalloffandonsiteACpowergeneration capacity; this is generally known as station blackout (SBO). In common with theinitiating events, an evaluation of safety margins is requested along with a review of whatimprovements,ifany,couldbeappliedtoimprovemarginsandtoremoveorreducefurthertheprobabilityofcliffedgeeffects.

31 Forlossofultimateheatsink,initiallythenormalcoolingsystemsareconsideredunavailable,andthenprogressivelossofalternativeandbackupcoolingsystems(BUCS)isreviewed.

32 For the final sequence, a loss of ultimate heat sink alongwith SBO is considered. This is anextreme fault conditionand the stress tests then look for informationonhow the faultwouldescalateintoasevereaccidentandthetimescalesinvolved.Areviewofpotentialmarginsandofimprovements, if any,which could be applied to improvemargins and to remove or reducefurthertheprobabilityofcliffedgeeffects,isrequired.



33 Itisworthnotingthatcomplementaryworkonelectricalsuppliesandcoolingsuppliesisalreadyunderway in theUKasaresultofRecommendations IR17, IR18, IR19and IR20 inHMChiefInspectorsreportonFukushima(Ref.2)(seeAnnex6).

0.2.3 SevereAccidentManagement34 TheENSREGrequirementsforsevereaccidentmanagementrecognisethatmostsevereaccident

management arrangements are there to mitigate the worst effects, not to prevent themoccurring.

35 The reviewasks for thekeymanagement features toensure control, coolingand containmentalong with instrumentation to confirm key parameters, and for the potential accidentmanagementmeasureswhichcouldbeappliedbythelicenseestobeconsideredinasystematicmanner.

36 The review also builds on learning from Fukushima about damage to the local and regionalinfrastructureandcommunications,andthepotentialforalongdurationofstandaloneactivityatthe site in the face of major regional disruption. As before, potential cliffedges are to beidentified, alongwith anypotential improvements that could improvemargins and removeorreducetheprobabilityofcliffedgeeffects.

37 RecommendationsIR24andIR25ofHMChiefInspectorsfinalreport(Ref.2)arerelevanthere.

0.3 RelevantAspectsofUKRegulatoryRegime0.3.1 LegalFramework38 IntheUK,thelegalframeworkfornuclearsafetyisestablishedprincipallythroughthe:

HealthandSafetyatWorketc.Act1974(HSWA74).

NuclearInstallationsAct1965(NIA65)(asamended).

39 UnderHSWA74employersareresponsibleforreducingrisks,sofaras isreasonablypracticable,to their workers and others, including the public. This responsibility is elaborated further inrelationtonuclearsitesbyNIA65,whichestablishesanuclearsitelicensingregime.Thepowertogrant a licence to use a site to construct and operate a specified nuclear installation, and itssubsequentregulation,isvestedintheHealthandSafetyExecutive(HSE),whichfurtherdelegatesthis authority to HM Chief Inspector of Nuclear Installations. This power includes attachingconditions in the interests of safety or radioactivewastemanagement. These conditions arelegallyenforceable.

40 European legislation in the form of EC Directives is transposed into the UK legal frameworkoutlinedabove.ThemostrecentEuropeanlegislationistheNuclearSafetyDirective,whichcameintoforceinJuly2011.

41 ONR isanagencyofHSE,and istheprincipalregulatorofthesafetyandsecurityofthenuclearindustryintheUK;itsindependenceissecuredlegallythroughHSWA74.ONRwasformedinApril2011fromthreeformerbodies:theHSENuclearDirectorate,UKSafeguardsOfficeandOfficeforCivilNuclearSecurity. Inaddition,ONRrecentlytookonthenuclearregulatoryfunctionsoftheDepartmentforTransport,byincorporationoftheRadioactiveMaterialsTransportTeam.



0.3.2 Licensing42 RegulationofthesafetyofnuclearinstallationsintheUKisthroughasystemofcontrolbasedon

a licensing regimewithinwhicha corporatebody isgranteda licence tousea site for specificactivities.ThisallowsONRtoregulatethedesign,construction,operationanddecommissioningofanynuclear installationforwhichanuclearsite licence isrequiredunderNIA65.Nuclearsitelicences are granted for an indefinite term and a single licencemay cover the lifetime of aninstallation.

43 NIA65allowsHMChief InspectorofNuclear Installations toattach toeachnuclear site licencesuchconditionsasONRconsidersnecessaryordesirableintheinterestsofsafety,orwithrespecttothehandling,treatmentordisposalofnuclearmaterials.ONRhasdevelopedastandardsetof36LCs,whichare (withminorvariations)attachedtoallnuclearsite licences. Inthemain,theyrequire the licensee tomakeand implementadequatearrangements toaddress theparticularsafetyareasidentified.TheLCsprovidetheprimelegalmeansforONRsdaytodayregulationofsafetyatlicensedsites.Theydonotrelievethelicenseeoftheresponsibilityforsafety.Theyaremostly, but not exclusively, nonprescriptive, setting goals that the licensee is responsible forachieving.

44 One of the requirements of the LCs is that the licensees produce an adequate safety case todemonstratethatfacilitiesaresafeinbothnormaloperationandfaultconditions.Thesafetycaseisafundamentalpartofthelicensingregimeatallstagesinthelifecycleofanuclearinstallation.Itestablisheswhethera licenseehasdemonstrated that itunderstands thehazardsassociatedwithitsactivitiesandhasarrangementstocontrolthemadequately.

0.3.3 DesignBasis45 ONRhasdevelopedandpublisheditsowntechnicalassessmentprinciples,whichitusestojudge

licenseessafetycases;thesearesetoutintheSafetyAssessmentPrinciplesforNuclearFacilities(SAP)(Ref.8).ThelatestversionoftheSAPs,publishedin2006,wasbenchmarkedagainstextantIAEAsafetystandards.InadditiontotheSAPs,moredetailedTechnicalAssessmentGuides(TAG) accessible atwww.hse.gov.uk/nuclear/tagsrevision.htm are available to ONR assessors toassist them in making judgements on licensees safety submissions. The SAPs / TAGs alsoincorporatetheWENRAreference levels.IntheareasrelevanttotheaccidentattheFukushimasite, theSAPsandTAGs setout regulatoryexpectations forprotectionagainsthazards suchasextremeweather, flooding,earthquakes, fire,explosionetc.,and for theprovisionofessentialservices.

46 SpecificSAPsandsectionsoftheSAPsdefineONRsexpectationsforthedevelopmentofadesignbasis.

47 DesignBasisAnalysis (DBA)providesa robustdemonstrationof the fault toleranceofa facilityandof theeffectivenessof its safetymeasures. Itsprincipalaimsare toguide theengineeringrequirementsofthedesignandtodeterminelimitstosafeoperation.Inthisapproach,theriskisnot quantified but the adequacy of the design and the suitability of the safetymeasures areassessedagainstdeterministictargets.

0.3.4 ExternalHazards48 ONRsregulatoryexpectationsforassessmentandanalysisofexternalhazards,suchasextreme

weather, floodingandearthquakes,aresetout indedicatedprincipleswithin theSAPs (Ref.8).These principles represent highlevel requirements for identification of the external hazardsthemselvesand the scopeofanalysisexpected for suchevents.TheseSAPsareaugmentedby

http://www.hse.gov.uk/nuclear/tagsrevision.htm



more detailed guidance contained inONRs TechnicalAssessmentGuide T/AST/13 (Ref.9).Aswellasprovidingmoredetailedguidanceonidentificationandanalysis,thetechnicalassessmentguidemakesitclearthatlicenseessafetycasesshouldincludeconsiderationofsupportservicessuchasaccessroads,watersupplies,firemainsandsitecommunications,pointingoutthattheyshouldbedesignedand routed so that in theeventofanexternalhazardoccurring, sufficientcapability remains to perform the required safety functions. The technical assessment guideincludesalloftherelevantWENRAreferencelevels.

0.3.5 FaultAnalysis49 Conservativedesign,defenceindepth,goodoperationalpracticeandadequatemaintenanceand

testingshouldminimisethelikelihoodoffaults.TheDBAshouldensurethatthefacilityhasbeendesignedtocopewithorwithstandawiderangeoffaultswithoutunacceptableconsequencesbyvirtueoftheplantsinherentcharacteristicsoritssafetyfeatures.

50 InadditiontoDBA,forcomplexfacilities,ProbabilisticSafetyAnalysis(PSA)mayalsobeusedtoconfirm that the overall risk presented by the facility lieswithin targets set by the licenseesthemselvesandbyONRintheSAPs(Ref.8).PSAcanalsohelpunderstandthepotentialstrengthsandweaknessesofthedesign,particularlyinlightofthecomplexdesignsandinterdependencies,andhelpsecurebalance.

51 DBA may not include the full range of identified faults because it may not be reasonablypracticable tomake design provisions against extremely unlikely faults. Itmay not thereforeaddresssevere,butveryunlikely, faultsagainstwhichthedesignprovisionsmaybe ineffective.Thisisaddressedbysevereaccidentanalysis.

0.3.6 SevereAccidentManagement52 Theprincipleofdefenceindepth requires that faultsequences leading tosevereaccidentsare

analysed and provisionmade to address their consequences. The analysis of severe accidentevents shouldbeperformedon abestestimatebasis to give realistic guidanceon the actionswhich need to be taken in the unlikely event of such an accident occurring. Severe accidentanalysismayalsoidentifythatprovidingfurtherplantandequipmentforaccidentmanagementisreasonablypracticable.

53 AlloftheUKNPPsandsignificantNPGNFinstallationshadDBA,PSAandsevereaccidentanalysisundertakenduringtheirdesignor inasubsequentPeriodicSafetyReview(PSR).Thestresstestsprocesseffectivelyundertakesatargetedreviewofspecificextremeexternalhazardswithlossofkeysystemsandhence,severeaccidentstudiesinasystematicmanner.

0.3.7 PeriodicSafetyReview54 IntheUKtheoperatorofanuclearinstallationisrequiredbyaspecificlicencecondition(LC15)to

periodicallyreview itssafetycasefortheplant.ThisPSRusuallytakesplaceeverytenyearsandrequirestheoperatortodemonstratethattheoriginaldesignsafetyintentisstillbeingmet.Thereassessment is performed against the latest safety standards, operational experience andtechnicalknowledge.Theoperatingexperienceoftheplantisalsoconsideredinthereview.IfthePSRidentifiesanyreasonablypracticablesafetyimprovements,thenitisalegalrequirementthatthese shouldbemadeby the licensee.ThePSR includesa reviewof the safetyof theplant inresponsetoeventssuchasearthquakes,floods,fireandexplosion.ONR independentlyassesseslicenseesPSRreportsusingitsSAPsandTAGs.



55 ThePSRsforeachsitetakeaccountofmodernstandardsandrecentresearchfindings.Overthelast two decades, a number of tsunami and flooding studies have been completed by theUKnuclear industryorhavebeen commissionedbyGovernment. Theoutputs from these studieshavebeenconsideredinthesubsequentPSRs.

0.3.8 RadiationEmergencyPreparednessandPublicInformationRegulations56 The requirements for the preparation of emergency plans are principally covered by the site

licence issued to a nuclear site underNIA65 and theRadiation (Emergency Preparedness andPublic Information)Regulations2001(REPPIR).Wherethere isapotentialforanoffsitereleaseof radioactivity that would require implementation of countermeasures, detailed emergencyplanning zones (DEPZ)areprovidedaround the installations.The requirements foraDEPZarestipulatedwithinREPPIR.

0.3.9 ContinuousImprovement57 This philosophy is at the core of the UK requirements for the nuclear industry through the

applicationoftheaslowasreasonablypracticable(ALARP)legalrequirement,andisthewayinwhichsustainedhighstandardsofnuclearsafetyarerealised.Itmeansthat,nomatterhowhighthestandardsofnucleardesignandsubsequentoperationare,thequestforimprovementmustnever stop. Seeking to learn from events, and from new knowledge and experience, is afundamentalfeatureofthesafetycultureoftheUKnuclearindustry.

58 AllUKnuclearsite licenseeshaveprocessestoassimilate,reviewanddisseminate lessons learntfrom significant events both in the UK and overseas. These arrangements are part of thecontinuousimprovementandOPEXfeedbackprocesseswhichareexpectedofalllicensees.

0.4 LicenseesCoveredbytheScopeofNPGNFStressTests59 Thisreportcoversmanylicensees,morethanfortheNPPstresstestsperformedtotherequestof

EC.Thelicenseesandassociatedlicensedsiteshavegenerallynocommoncharacteristics,asNPPoperatorsmaypresent;however,theymaybegatheredasnecessarybysimilarityofactivitiesorstage of plants in their lifecycle, as done within ONR, through several programmes(www.hse.gov.uk/nuclear/onrprogrammes.htm). The widescope covered has called on fourdifferentONRProgrammes, including theoneswhoreported inDecember2011onstress testsforNPPs.

60 Thereare16NPGNFlicenseescoveredinthisreport,includingfiveofthemdedicatedtodefenceactivitiesdescribedbelow,andtwoofthemrelatedtoformerorfutureNPPs.

0.4.1 DefenceLicensees61 TheMinistryofDefence(MoD)isresponsibleforaNavalNuclearPropulsionProgramme(NNPP)

andNuclearWeaponsProgrammeforthepurposesof:

Producingandmaintainingnuclearweapons.

Buildingnewnuclearpoweredsubmarines.

Provingandunderwritingthedesignandperformanceofsubmarinenuclearreactorsandfuelassemblies.

http://www.hse.gov.uk/nuclear/onr-programmes.htm



Producingthefuelandcoreforsubmarinenuclearreactors.

Maintainingandrefuellingnuclearsubmarines.

62 MoDMinistersaccounttoParliamentonnuclearsafetymattersonallthesesites.

63 CertainofthesitesintheDefenceNuclearProgrammeareownedandmanagedbytheMoDitselfandactivitiesthereareexemptedfromsomepartsofcivilnuclearregulationdueeithertocrownimmunityor the formaldisapplicationofparticular legislation, including theexclusionofNIA65fromnuclearreactorscomprisedinameansoftransport(i.e.submarines).MoDisnotexemptedfrom HSAW74, the Ionising Radiations Regulations 1999 (IRR) or REPPIR and ONR regulatesactivitiesonthosesitesthataredirectlyoperatedbytheMoDundertheseandotherlegislation.

64 Withinthisreport,thedefencelicenseesareAtomicWeaponsEstablishment(AWE),RollsRoyceMarine PowerOperations Ltd (RRMPOL), BAE SystemsMarine Ltd (BAESM), Devonport RoyalDockyardLtd(DRDL)andRosythRoyalDockyardLtd(RRDL).

65 TheremainderofthesitesintheDefenceNuclearProgrammearemanagedbytheprivatesector,contractedtoprovidenuclearservicestotheMoDthroughavarietyofcommercialarrangementstheserangefromtheGovernmentowned,contractoroperated(GOCO)sitesatAWEthroughtosites thatareprivatelyownedandmanagedsuchasBAESystems inBarrowandRollsRoyce inDerby. The generality of activities on these sites falls under the remit ofNIA65 and the sitesconcernedarethereforelicensedbyONR,albeitduetospecificdisapplicationofNIA65ONRdoesnot in any case regulate the design of submarine nuclear reactors, nor the design of nuclearweapons.

66 WhereverexemptionsordisapplicationsofcivillegislationexistitisMoDpolicytoensure,wherereasonablypracticable,thatstandardsareat leastasgoodasthoserequiredbycivilregulation.TheDefenceNuclearSafetyRegulator (DNSR)providesassurance to theSecretaryofState forDefence, through theDefenceNuclearSafetyBoard, that standardsofnuclearand radiologicalsafetyareappropriatelymaintainedfortheparticularsitesandactivitieswheretheexemptionsand disapplications apply. To this end DNSR oversees a system of Authorisation of MoD'sdutyholderswhodirectlycontrolnuclearactivitiesDNSR'sAuthorisationsystemcloselyparallelsONRs Licensing system. The formal basis of the relationship is covered in a MoD / HSEAgreementandanassociatedLetterofUnderstandingwhichdescribestheworkinglevellogisticsandjointregulatoryframework.

67 DNSR, forMoD, is carryingout itsown assessmentofAuthorisee responses equivalent to theFukushima stress tests.DNSR isobliged to consider thenuclear safety implications relating todesignoftheMoD'snavalreactorplant(NRP)anddesignoftheMoD'snuclearweapons,whichfalloutsidetheregulatoryviresofONRduetodisapplicationofNIA65fortheseaspects.Thus,inthisreport,ONRonlyconsiderstheresponsesfrom licenseesand implicationsfornuclearsafetyregardingthoseactivitiesandfacilitiestowhichNIA65doesapply.

68 ONR has assessed the source submissions and supporting source material supplied by thedefencelicenseesandhasreturnedallsuchinformationbacktothelicensee.Thisreportpresentsasummaryoftheirsubmissionsattheappropriatesecurityclassificationforthisreport.

0.4.2 EDFEnergyNNBGenerationCompanyLtd(NNBGenCo)69 NNBGenCoisnotcurrentlyanuclearlicensee;ithasappliedtobecomethenuclearsitelicensee

fortheproposednuclearlicensedsiteofHinkleyPointC.TwoUKEPRNPPsareproposedtobeconstructedatHinkleyPointC.ItwasdecidedtocovertheNNBGenCoHinkleyPointCsiteintheNPGNF report because currently no nuclearrelated construction has been undertaken onsite



andas such itdidnotmeet theENSREG requirement for inclusion in thenational final reportdedicatedtoNPPs.

0.5 ProcessforStressTestsActivities0.5.1 OverviewandTimeline70 The assessment process was required to commence in June 2011 and the licensees were

informedofthisbyONR.

71 ThenextmajorstepwasforthelicenseestosubmittheirstresstestsprogressreportsbytheendofOctober2011 thiswas completed ina timelymanner.ONRhas reviewed the informationsuppliedandproducedtheUKProgressReport(Ref.7)on6December2011.

72 The licenseescontinuedworkontheirmainstresstestsreportsandsubmittedthemtoONRbytherequireddateof31December2011(Refs11to27h).

73 ONRassessedthisinformation,andpublishedtheUKRegulatorsReportthisreport.

74 To help the Fukushima response, activitiesmove from a unique reactive process into normalregulatory business, which can then be regulated within the existing tried and testedarrangements.Thelicenseeshavebeenaskedtoproducefurtherreportsinthesummerof2012respondingtoHMChiefInspectorsfinalreportrecommendationstoprovideanupdatetotheirstress testsreportsand toproduceaconsistent,combinedoverallworkprogramme.ONR thenintendstoproduceanImplementationReportaboutayearafterHMChiefInspectorsfinalreporttoprovideanupdateonprogressinimplementingthelessonsfortheUKsnuclearindustry.

0.5.2 LicenseeProcessesforProducingStressTestsReports75 IntheUK,inlinewiththegoalsettingnonprescriptiveapproachtoregulation,thelicenseeswere

expected toprepare the informationand the initialassessments foreach site.TheoutputhasbeenassessedbyONR toconfirm that it isappropriateand that the licenseeshaveadequatelyconsideredthesafetymarginsandhowtheymightbeextended.

76 The approach adopted bymany licensees was to apply the arrangementsmade under LC15(periodicreview)tocarryoutareviewandreassessmentofsafetyandsubmitareporttoONR.This provided a structured framework for the review activities and gave clarity of roles andfunctionswithin the licensees arrangements for thepreparation, review and reassessmentofsafetycaseinformation.

77 Thekeyoutputsfromthestresstestsprocess,beyondthereportsthemselves,aretheareasofpotential improvement.Wherepotential improvements toprocessesor equipmenthavebeenidentifiedby the licensees, theyhave reported themasConsiderations.TheseConsiderationsdonotrepresent finalor formalcommitmentstomakespecific improvements.Rathertheywillbe taken forwardby the licensees forexaminationbyadecisionmakingprocess todeterminewhich of the potential improvements isALARP, andwhich should therefore be implemented.Licenseesmay still choose to implement improvementswhich are not required tomeet theALARPprinciple,perhapsforcommercialorpublicrelationsreasons.Thedecisionmakingprocessandhow it isappliedand the timescales for implementationof those improvementswhichareadoptedareclearlyareasofinteresttoONR.Licenseeswillberequiredtojustifyanydecisionnottoadoptaparticularmeasure,inlinewithONRsnormalregulatoryprocess.



0.5.3 ONRsAssessmentProcess78 ONRappliesa targetedsamplingprocess toalmostallof itsactivities. In thecaseof thestress

tests reports submitted by the licensees, a team of specialist inspectors has assessed specificsectionsofreportsandlookedathowtheyhavebeenappliedgenericallyacrossthesites.ONRsdetailed assessment has covered all of the key discipline areas of external hazards seismic,flooding andweather aswell aselectrical and system fault studies and severe accident andemergencyresponsetopicareas.

79 By using a variety of approaches to inspection and assessment,ONR has developed a broadunderstanding of how the stress testswere applied aswell as how they are reported by thelicensees.ONR has confirmed that the licensees havemet the ENSREG requirements for thestresstestsand itsreporting,buttakingawiderviewofhowthestresstestshavebeenappliedhas given ONR a much greater understanding of the particular strengths and weaknessesreportedbythelicensees.

80 During thedevelopmentof stress tests reports,ONRs teamof specialist inspectors interactedwithlicenseesinavarietyoftechnicalmeetingsandinspections;thisapproachsecuredassurancethat licenseearrangementsforassessmentaccordedwithENSREGexpectations (insofarastheywererelevanttotheirrespectiveoperations).ONRsassessmentoflicenseesstresstestsreportshasresulted inanumberofstresstestsfindingsasdetailed intheExecutiveSummary.SomeofthesefindingsreinforceorextendConsiderationsidentifiedbythelicensees;othersareadditionaltothosealreadyidentified.

81 This report details a number of topics identified by some licensees during their respectiveassessments that require further consideration for potential areasof improvement. These arelistedasConsiderations.ONRhasastronginterestinthedecisionmakingprocessappliedbythelicenseestotheirConsiderations,andthefirststresstestsfindingistoensureONRretainsaclearviewoftheprocessanditsoutputs.

STF20: Sellafield Ltd, AWE, RRMPOL, BAESM, DRDL, RRDL,Magnox Ltd and NNB GenCoshould provide ONR with the decisionmaking process to be applied to theirConsiderations along with a report which describes the sentencing of all theirConsiderations. The reportwill need to demonstrate toONR that the conclusionsreachedareappropriate.

82 It should be noted that the findings described in this report are supplementary to therecommendationsraised inHMChiefInspectorsreports inthattheygenerallyrelatetospecificaspects of those recommendations. They are also supplementary to the findings andConsiderationsraised inONRsNationalStressTestsFinalReportforUKNPPs(Ref.10).Theydonotsupersedeanyexisting issuesornecessary improvements identifiedbyONRvia thenormalregulatoryengagementprocesses.Commitmentsaredistinguishedfromstresstestsfindings,andConsiderations,inthatONRhasalreadyreceivedawrittenundertakingforresolutionofaqueryorissue.

0.5.4 ONRsReportingProcess83 ONRhasfollowedthestructureandcontentsofthestresstestsreportasdefinedbyENSREGas

faraspossible.

84 ThestructuregenerallyhasadescriptionoftheinformationprovidedbythelicenseesfollowedbyONRs view of that information. This should allow the reader to be clear when a point orcommentistheinformationsuppliedbythelicenseesorwhenitistheviewoftheRegulator.



85 AdraftofONRsreportwascriticallyreviewedbytheTAPwhichwassetuptoprovideHMChiefInspector of Nuclear Installations with independent advice following the Fukushima events.AdvicefromtheTAPhasbeenconsideredindetailandthereportamendedaccordingly.



1 GENERALDATAABOUTTHESITESANDNPGNF86 ThelocationsofUKNPGNF(asdefinedbyexclusionfortheECstresstests)areshownonthemap

below(Figure1).Italsoshowsthe locationofoneproposednuclearpowerstationsite(HinkleyPointC)forwhichanapplicationforanuclearsitelicencehasbeenreceivedbyONR;authorisedsitesoftheMoDarealsoshownonthemap.

Figure1:MapofnonPowerGeneratingNuclearFacilities



1.1 BriefDescriptionoftheSiteCharacteristics

SellafieldLtdSellafieldandWindscale

87 The Sellafield nuclear licensed site is owned on behalf of HerMajestys Government by theNuclear Decommissioning Authority (NDA), and is operated by the sitelicensed companySellafieldLtdundertheshareholdingoftheNuclearManagementPartners.Sellafieldisacomplexanddiversesitewhichincludesdecommissioningreactors,spentfuelstorageponds,reprocessingplants, waste treatment plants and waste storage plants. The site, which currently employsapproximately10,000fulltimeequivalentstaff, is locatedontheWestCumbriancoastadjacentto the Irish Sea on the western outskirts of the Lake District National Park and within thecatchments of the Rivers Calder and Ehen. The sitelicensed boundary encompasses anapproximateareaof276hawithintheCopelandDistrictofthecountyofCumbria.ThemajorlocaltownsofWhitehaven,WorkingtonandBarrowareapproximately14kmtothenorth,25kmtothenorthand38kmtothesoutheastrespectively.Thereareabout200people livingwithin2kmofthesite:thenearestsettlementofanysizeisSeascale2.5kmdistant,withapopulationofabout1800.TheSellafieldsiteisaccessedviafourprincipalpedestrian/vehiculargatesallleadingfromthenorthsouthA595singlecarriagewaywhichpasseswithinapprox.1.5kmoftheSellafieldsitenearCalderbridge.TheCumbriancoastaltrainlinehasarequeststopatSellafieldstation.

88 Thesitetopographicalrangeis9to48maboveordnancedatum(AOD).

SellafieldLtdCapenhurst

89 The Sellafield Ltd Capenhurst site is located approximately 10km to the north of Chester,approximately6kmsouthwestoftheRiverMerseyand6kmnortheastoftheRiverDee.Thesiteis generally flatwith a slight incline to the easternboundaryof the site. The site topographicrangeis35to40mAOD.ThelicenceholderisSellafieldLtd,whooperatesthesiteundercontractwith theNDA.Currently thereare two separate licenseeswithin theCapenhurst siteboundary(Sellafield Ltd andUrencoUK Ltd) both licenseesmaintain close association for a number ofservices,includedaccidentmanagement.Currently,aSiteIntegrationProjectisbeingcarriedout

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