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 Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. Safety 　 Regulation- 1 -Deterministicvs.Probabilistic/ Fukushima- July26,ThirdPeriod Hiroshi UJITA Tokyo Institute of Technology 1  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. 2 Quy chế và an toàn • Therearegrowingtendencyintheorganizationalproblemandalsotheimpactontheenvironment, duetowidespreadandcomplextargetsystem. • ShiftfromprescriptiveRegulationtoNormativeRegulation. • Thelegalsystemchangesfromresultstheorytoacttheory(backgroundtheory,proceduretheory, frameworktheory). • Theshiftfromthepunishmentduetoaccidentoccurtothepunishmentduetonottomakethe mechanismtopreventtheaccident. • AsforthePerformanceStandardRegulationintheU.S.,Risk-InformedPerformance-Based Regulationhasbeenadoptedbasedontherisktheory. • AsfortheRegulatoryorganization,SafetyandEnvironmentalRegulatoryAuthorityshouldbe establishedasintheCabinetOffice,withunifiedlookthroughouttheorganizationand independenttotheotherauthorities.CreateanInstituteforEnvironmentandSafetyand EnvironmentandSafetyAdvisoryCommitteetodeveloppolicies.  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. 3 LawandSafety • Recently,frequentoverstuffedcorporatescandalsandaccidents. • Responsiblepersonwillfulnegligence,thatisinactionbytheostrichfashion “hadbeenpredictedwhiledidnotconsider,”istheworst. • Sincethelawhasbeendesignedfororganizationalaccidentprevention primarily,itworksbycombiningbothtechnicalandlegalmeasurestoimprove safetymeasures. • Inaddition,economicandsocialsanctionsandprocedureandframeworktheory, etc.arealsorequired. • Asforthesocialandeconomicsanctionsagainstorganizationalaccidents, punitivecompensationsystemshouldalsobeconsidered.  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. • Preventingdamage • Failureexpansionmitigation:autonomouscharacteristic,inherentsafety (intrinsicallysafety) • Accidentprevention:afail-safe,fool-proof,redundancy,diversity • Accidentexpansionmitigation:confinement,controlrelease • Environmentaleffectsmitigation:evacuation – Focusonpreventingdamage,expansionmitigation,oraccident preventiontotheforefront – Increasedattentiontoback-upsystems,ifithasalargeenoughimpact ontheenvironment 4 DefenseinDepthforthesafetydesign  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. • Deterministicapproach: • Safetyassessmentforeachbarriertodefenseindepth – Themostsevereeventisassumedtorepresentthetypicalevent,whilethe initiatingeventsareconsideredandclassifiedbybehavior(DesignBasis Accident) – Inadditiontothis,assumingthatfailureofoneofthemostimportantsafety- relatedequipment(SingleFailureCriteria), – Wemayguaranteethesafetybasedontheevaluationthatwecanstillhave enoughsafetyonthatseverehypothesis. – SingleFailureCriterionfailure • LOCA,LossofCoolantAccident,therealitywillnothappen(NRC) • Transientisthemostlikelyevent(ReactorSafetyStudy1975,TMI Accident1979) 5 SystemSafetyEvaluation1  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. • Probabilisticapproach: • Overallsystemsafetyassessmentbasedontheconceptofrisk – Easilysecuredcoverageofeventsintheprocessofconsideringtheprobability – Rationaldecisionsduetothepresenceofriskevaluationcriteria -SafetyGoals:aquantitativediscussion“howsafeissafeenough” – Determinationofquantitativesafetytrendthroughoutthelifecycle – Evaluationofsafetymeasuresimplementedashardwareattheinitialsystem construction – Evaluationofdailysafetyfromenteringthecommercialoperation • Determininginspectionfrequency,acceptablewaitingtime,etc.areinherently risk-based • Chemicalplants:extensionoftimespanofperiodicinspection;1yearto2years – Eventsoflargeuncertaintiesanddifficulttopredictcanbequantifiedasanexpert judge • Seismic(Tsunami)riskassessment,humanreliabilityassessment 6 SystemSafetyEvaluation2  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. 7 Themethodologyforsafety DeterministicApproachUseBothApproachesProbabilisticApproach DesignMethod231 ManagementMethod122 EvaluationMethod243   4:Excellent3: Good2:Fair1:Poor  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. • (Successpathmethod–MissionCritical;Space,Missile) • PRA(ProbabilisticRiskAnalysis)SafetyCritical – ETA/FTA(EventTree/Faulttreeanalysis) – HRA (Human Reliability Analysis) – CMF (Common Mode Failure) Analysis • QRA(QuantitativeRiskAnalysis) – HSE(Health&SafetyExecutive) – ISO(InternationalStandardOrganizations) • FMEA(FailureMode&EffectAnalysis) • HAZOP(HazardousOperabilityStudy) 8 Methodologyofrisktheory  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. Study of internal initiating event Analysis of the accident sequences leading to core damage Analysis of the accident sequences leading to loss of containme nt function Analysis of core damage accident progressi on phenome na Core Damage Frequency Source term to atmosphere Analysis of public exposure to atmospheric dispersion risk Study of external initiating events Accident mitigation system reliability analysis Human reliability analysis Occurrence frequency of each phenomenon Frequency of containment function Loss Level1 PSA Level2 PSA Level3 PSA ProbabilisticRisk(Safety)Assessmentprocedure 　 9 Fukushima Daiichi Accident  Nuclear Power Engineering at Electric Power University Copyright © 2011 Tokyo Institute of Technology All Rights Reserved. 　　 Level1PSA 　 Initiating Event Success Criteria Plant Survey HumanError Dependent Failure Uncertainty 　　 study Sensitivity 　　 analysis ComponentFailureRate Model (Coredamage frequency) Accidentsequence quantification FaultTree EventTree Phenomenapropagationscenario 10 [...]... for 52 Plants in Japan 10 10 -4 PSA Result of Internal Event in  Normal Operation for 52 Plants  shows to be less than  performance goal Index 2: Containment Failure Frequency 1 0-5 1 0-6 Index 1: Core Damage Frequency   -3 BWR PWR 1 0-7 1 0-8 1 0-9 1 0-1 0 1 0-1 0 1 0-9 1 0-8 1 0-7 1 0-6 CDF (1/(r.y)) 1 0-5 1 0-4 NISA, PSA Methodology After Accident  Managemant Published (Oct.2004)  1 0 -3 Copyright © 2011 Tokyo Institute... Explosion Melt- Concrete Interaction Copyright © 2011 Tokyo Institute of Technology All Rights Reserved 17 Nuclear Power Engineering at Electric Power University 100   FP release and accident  propagation are  categoraized by same way 1 0-1 Source Terms (-) Radioactive Release  to Atmosphere Group 1 & Group 5 Group 3 Group 3. & Group 3 &Group 4 Group 5 1 0-2 Group 2 Group 2 & Group 4 -3 10 1 0-4 1 0-5 1 0-6 FP release will decrease ... time to PCV failure to core  melt initiation prolonged 1 0-7 -1 0 0 10 20 30 Time to PCV Failure from Core Melt Initiation (h) Failure location Xe CsI Sr Drywell × ● ○ Gas space in wetwell + ▲ △ Bottom of wetwell (liquid part) ＊ ■ □ Copyright © 2011 Tokyo Institute of Technology All Rights Reserved 18 Nuclear Power Engineering at Electric Power University Level3PSA 　 Level2 PS A Source Term Release tendency  ...  =A*B1+A*B2 AND gate   (Minimal Cut set) Safety Function A Loss Safety Function B Loss OR gate P(A+B+C) =P(A)+P(B)+P(C) -P(AB)-P(BC)-P(CA) +P(ABC) Safety Function B1 Loss Safety Function B2 Loss P(ABC) =P(A)P(B)P(C) Copyright © 2011 Tokyo Institute of Technology All Rights Reserved 13 Nuclear Power Engineering at Electric Power University Level1PSA: Fault tree (FT) Low Pressure Core Injection System... exceptional circumstances. This has been greatly assisted by highly professional back-up support,  especially the arrangements at J-Village to secure the protection of workers going on sites • The Japanese Government’s longer term response to protect the public, including evacuation, has  been impressive and extremely well organized. A suitable and timely follow-up programme on public  and worker exposures and health monitoring would be beneficial • The planned road-map for recovery of the stricken reactors is important and acknowledged. It will ... Electric Power University IAEA International Fact Finding Expert Mission of the Nuclear Accident following the Great East Japan Earthquake and Tsunami Tokyo, Fukushima Dai-ichi NPP, Fukushima Dai-ni NPP and Tokai NPP,  Japan, 24 May- 1 June 2011, Preliminary Summary   • The Japanese Government, nuclear regulators and operators have been extremely open in sharing  information and answering the many questions of the mission to assist the world in learning lessons to ... conducted for energy prediction during the 21st Century in the world.  Taking the effort for energy-saving as major premise, carbon-sequestration for fossil fuel, renewable  energy and nuclear energy should be altogether developed, which means energy best mix is achieved,  under the CO2 constraint around 450ppm atmosphere.  Nuclear phase-out scenario, in which new nuclear plant construction is prohibited, is possible even ... Electric Power University IAEA International Fact Finding Expert Mission of the Nuclear Accident following the Great East Japan Earthquake and Tsunami Tokyo, Fukushima Dai-ichi NPP, Fukushima Dai-ni NPP and Tokai NPP,  Japan, 24 May- 1 June 2011, Preliminary Summary   • The tsunami hazard for several sites was underestimated. Nuclear designers and operators should appropriately  evaluate and provide protection against the risks of all natural hazards, and should periodically update these ... May 9th, 2011, Technical Analysis Subcommittee, Committee for Nuclear  Safety Investigation, Atomic Energy Society of Japan - Summary of Strongly Recommended Actions   1. Hardware preparation to protect the safety System, Structure and Components (SSC) from tsunami 2. Preparation for variety of power sources, such as air‐cooled gas turbine system 3.  Consideration and preparation for variety of cooling systems in addition to seawater cooling system... Copyright © 2011 Tokyo Institute of Technology All Rights Reserved 23 Nuclear Power Engineering at Electric Power University Energy issue and role of nuclear energy after the  Fukushima Daiichi Accident • •   • • • • • Premise here is that "Global warming is an invariant problem!“ –  "Energy security is also an invariant problem!"  The long-term energy demand and supply simulation to minimize the total energy system cost was  . 3. & Group 5. 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 -1 0 0 10 20 30 Source Terms (-) Time to PCV Failure from Core Melt Initiation (h) Group 3. & Group 4. Group 3. Group 2. & Group. Reserved. 13 Faulttreeanalysis (EachfunctionofDefenseinDepth) SafetyFunctionSLoss SafetyFunctionB2LossSafetyFunctionB1Loss SafetyFunctionBLossSafetyFunctionALoss ANDgate ORgate P(A+B+C) =P(A)+P(B)+P(C) -P(AB)-P(BC)-P(CA) +P(ABC) P(ABC)=P(A)P(B)P(C) S=A*B =A*B1+A*B2 (MinimalCutset)  Nuclear Power Engineering. Tokyo Institute of Technology All Rights Reserved. Safety 　 Regulation- 1 - Deterministicvs.Probabilistic/ Fukushima - July26,ThirdPeriod Hiroshi UJITA Tokyo Institute of Technology 1  Nuclear