ML18026B097

Mitigating Strategies for Beyond-Design-Basis External Events

ML18026B097
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Issue date:	01/26/2018
From:	Eric Bowman Beyond-Design-Basis Management Branch
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Andrukat D
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ML18026B126	List: ML18026B088 ML18026B097 ML18026B110
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Mitigating Strategies for Beyond-Design-Basis External Events Eric BowmanSpecial Advisor, Beyond-Design-Basis Management

Background

On March 11, 2011, a major earthquake struck off the coast of Honshu, resulting in a

large tsunami that caused widespread

devastation and significantly affected the

infrastructure and industry in the

northeastern coastal areas of Japan. This

led to damage to the nuclear fuel at Fukushima Dai-ichi Units 1, 2 and 3.

2 NTTF Tier 1 Actions*Order EA-12-049 on Mitigating Strategies*Order EA-12-050 (now EA-13-109) on BWR Vents

• Order EA-12-051 on Spent Fuel Pool Instruments

• Seismic and Flooding Walkdowns

• Seismic and Flooding Re-evaluations

• Staffing and Communications Assessments 3

Principles for Mitigating StrategiesIn examining the operating experience at Fukushima Dai-ichi, the NRC noted that many of the post-9/11 strategies in the U.S. may have helped lessen the effects of the event. The NRC also noted that strategies similar to these were attempted by the operators at Fukushima Dai-ichi during the event.Major differences exist between the localized damage assumptions of the post-9/11 strategies and the widespread damage in the operating experience in Japan.

4 Order EA-12-049 March 12, 2012 Licensees or construction permit holders shall develop, implement, and maintain

guidance and strategies to maintain or

restore core cooling, containment and spent

fuel pool cooling capabilities following a

beyond-design-basis external event.

5 Order EA-12-049 Continued*Simultaneous loss of all ac power and loss of normal access to the ultimate heat sink*Adequate capacity to address challenges to core cooling, containment, and spent fuel pool cooling capabilities at all units on a site*Reasonable protection of associated equipment

• Capable of implementation in all modes

• Procedures, guidance, training, and acquisition, staging or installing of equipment 6

NEI 12-06 Site Assessment Process 7

8 BWR FLEX Baseline Capability SummarySafetyFunctionMethodBaselineCapabilityCoreCoolingReactorCoreCooling

• RCIC/HPCI/IC

• DepressurizeRPVforInjection withPortableInjectionSource

• SustainedSourceofWater

• Useofinstalledequipmentforinitialcoping

• Primaryandalternateconnectionpointsfor portable pump

• MeanstodepressurizeRPV

• Useofalternatewatersupplytosupportcoreheat removalmakeupKeyReactorParameters

• RPV Level*RPVPressure

• (Re-)Poweredinstruments

• Otherinstrumentsforplant-specificstrategiesContainmentContainmentPressureControl/HeatRemoval

• ContainmentVentingor AlternativeContainmentHeat Removal

• Reliable,hardenedvent(perEA-12-050forMkIandII)orothercapability.ContainmentIntegrity(BWRMarkIIIContainments Only)*Hydrogenigniters

• Re-poweringofhydrogenigniterswithaportable powersupply.KeyContainmentParameters

• ContainmentPressure

• SuppressionPoolTemperature

• SuppressionPoolLevel

• (Re-)PoweredinstrumentsSFPCoolingSpentFuelCooling

• MakeupwithPortableInjectionSource*Makeupviahosesdirecttopool

• MakeupviaconnectiontoSFPmakeuppipingor othersuitablemeans

• Sprayviaportablenozzles S F P P ara m e t er s*S F P L e v el*P e r EA 12-051 9 Example BWR Licensee Flow Diagram 10 PWR FLEX Baseline Capability SummarySafetyFunctionMethodBaselineCapabilityCoreCoolingReactorCoreCooling&Heat Removal(steam generators available)*AFW/EFW*DepressurizeSG forMakeupwith Portable InjectionSource

• SustainedSourceofWater*Useofinstalledequipmentforinitialcoping*Connectionforportablepumpto feedrequiredSGs*Useofalternatewatersupplyto supportcoreheatremovalRCSInventoryControlandCore HeatRemoval(shutdownmodes withsteam generatorsnot available)*LowLeakRCPSealsand/orRCShigh pressure makeup*AllPlantsProvideMeansto Provide BoratedRCSMakeup*Low-leakRCPsealsand/orprovidingon-sitehighpressureRCS makeupcapability*Diversemakeupconnectionsto RCSforlong-termRCSmakeup andshutdownmodeheatremoval*Sourceofboratedwater*LetdownpathifrequiredKeyReactorParameters*SGLevel*SGPressure*RCSPressure

• RCSTemperature*(Re-)PoweredinstrumentsContainmentContainmentPressureControl/HeatRemoval*ContainmentSpray*Connectionpointoncontainmentsprayheaderforuse with portablepumporalternatecapabilityoranalysisdemonstrating thatcontainmentpressure controlisnotchallenged,e.g.,MAAP analysis.ContainmentIntegrity(IceCondenserContainmentsOnly)*Hydrogenigniters*Re-poweringofhydrogenigniterswitha portablepowersupply.KeyContainmentParameters*ContainmentPressure*(Re-)PoweredinstrumentsconsistentSFPCoolingSpentFuelCooling*MakeupwithPortableInjectionSource*Makeupviahosesdirectto pool*Makeupviaconnectionto SFPmakeuppipingorothersuitable means*Sprayviaportablenozzles SFP P a r a m ete r s*SFP L e v e l*P er E A 12-051 11 Example PWR Licensee Flow Diagram Additional Mitigating Strategies Characteristics*Strategies based on plant-specific analyses*Time constraints identified with basis to show they can be met*Ability to use portable pumps for RPV/RCS/SG makeup

• Spare equipment

• Maintenance and Testing

• Training 12 Off-site Resources*Licensees have set up off-site resource centers to provide additional equipment

and supplies*24 hour delivery time

• Transportation by road or by air 13 National SAFER Center Locations 14 Alternative Approaches NEI 12-06 provided one acceptable approach. Others that have been proposed

include:*Additional hardened generators

• Repowering installed pumps

• Other minor differences from NEI 12-06 15 MBDBE Rulemaking*Integrated Response Capability in new 10 CFR 50.155*Adds requirements for reevaluated seismic and flooding hazard mitigation*Specifies removal of requirements during decomissioning 16 Risk Credit for Mitigating Strategies*U.S. Power Reactor Licensees are in the process of incorporating mitigating strategies in their Probabilistic Risk

Assessments of as built, as operated

plants*Degree of risk reduction varies based upon site and plant configurations 17 BibliographyDocumentAccession No.SECY-11-0093ML11186A950 Order EA-12-049ML12054A736 NEI 12-06, Revision 0ML12242A378 JLD-ISG-2012-01, Revision 0ML12229A174 NEI 12-06, Revision 2ML15348A015 JLD-ISG-2012-01, Revision 1ML15357A163 MBDBE RulemakingSECY-16-0142 18