NRC Perspectives on Reactor Safety Course
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NRC Perspectives on Reactor Safety Course Special Features of BWR Severe Accident Mitigation and Progression. Appendix 2B-7 Module 3 Section 7 Module 4 Section 7. L. J. Ott Oak Ridge National Laboratory. BWR Severe Accident Studies Were Conducted at Oak Ridge National Laboratory 1980-1999.

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L. J. Ott Oak Ridge National Laboratory

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L j ott oak ridge national laboratory

NRC Perspectives on Reactor Safety CourseSpecial Features of BWR Severe Accident Mitigation and Progression

Appendix 2B-7

Module 3 Section 7

Module 4 Section 7

L. J. Ott

Oak Ridge National Laboratory


Bwr severe accident studies were conducted at oak ridge national laboratory 1980 1999

BWR Severe Accident Studies Were Conducted at Oak Ridge National Laboratory 1980-1999

  • Follow-on to NRC Severe Accident Sequence Analysis (SASA) Programs initiated late 1980

    • Response to Three Mile Island

    • PWR studies

      • SNL

      • INL

      • LANL

    • BWR studies ORNL

  • Evaluations of Owners Group Emergency Procedure and Severe Accident Guidelines for NRR


Bwr severe accident technology activities at ornl

BWR Severe Accident Technology Activities at ORNL

  • Accident progression

    • Event sequence

    • Timing

    • Code application and model development

  • Analytical support of experiments

    • Pretest planning

    • Posttest analyses

    • Diverse locations

      • ACRR (Sandia)

      • NRU (Chalk River)

      • CORA (Karlsruhe)

  • Accident management strategies

    • Preventive

    • Mitigative

  • Extension to advanced reactor designs


Predicted bwr severe accident response is different from that expected of a pwr in several aspects

Predicted BWR Severe Accident Response Is Different from That Expected of a PWR in Several Aspects

  • Much more zirconium metal

  • Isolated reactor vessel

  • Reduction in power factor in the outer core region

  • Effects of safety relief valve actuations

  • Progressive relocation of core structures

  • Importance of core plate boundary

  • Steel structures in vessel

  • Large amount of water in vessel lower plenum


Boiling water reactor contributors to core damage frequency nureg 1150

Boiling Water Reactor Contributors to Core Damage Frequency – NUREG-1150


Station blackout involves failure of ac electrical power

Station Blackout Involves Failure of AC Electrical Power

  • Loss of offsite power

  • Emergency diesel-generators do not start and load

Short-Term

Station Blackout

Immediate Loss ofWater Makeup

Long-Term

Station Blackout

Loss of Water Makeup Following Battery Exhaustion


The most probable bwr accident sequence involving loss of injection is station blackout

The Most Probable BWR Accident Sequence Involving Loss of Injection Is Station Blackout

Peach Bottom

Short-term5%

Long-Term42%

Grand Gulf

Short-term96%

Long-Term1%

Susquehanna*

Short-term52%

Long-Term10%

Station Blackout Core

Damage Frequencies

*From Plant IPE (NPE 86-003)


L j ott oak ridge national laboratory

If the Reactor Vessel Remains Pressurized, Relocating Core Debris Falls into Water above the Core Plate

Grand GulfShort TermStation Blackout without ADS Actuation


Release of debris liquids through penetration internals has been extensively analyzed

Release of Debris Liquids through Penetration Internals Has Been Extensively Analyzed

  • Control rod drive mechanism penetrations: secure

  • Vessel drain: very improbable

  • Instrument tube: most likely internal path


L j ott oak ridge national laboratory

The BWR Control Rod Drive Mechanism Assemblies Are Held in Place by Upper Stub Tube Welds; the Incore Instrument Tubes Are Supported by Welds at the Vessel Wall


The drywell floor area is small and the drywell shell is within ten feet of the pedestal doorway

The Drywell Floor Area Is Small and the Drywell Shell Is Within Ten Feet of the Pedestal Doorway


Inside the reactor pedestal at peach bottom

Inside the Reactor Pedestal at Peach Bottom


Lower drywell at browns ferry

Lower Drywell at Browns Ferry


Bwr evolution

BWR Evolution


Comparison of esbwr and abwr

Comparison of ESBWR and ABWR

  • Key parameters that increase core flow in ESBWR

    • Shorter fuel

    • Tall chimney

    • Unrestricted downcomer


Safety systems inside containment envelope

Safety Systems Inside Containment Envelope


Breakdown by initiating event

Breakdown by Initiating Event


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