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Debris Effects in Long-Term Post-LOCA PWR Cooling. Graham WALLIS American Nuclear Society Northeastern Meeting October 23 2013 . Short-Term Cooling. 1960 “No need for ECCS” 1971 Public Hearing Creati o n of NRC LOFT RELAP TRAC 10CFR 50.46 Appendix K PCT<2200F

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Debris effects in long term post loca pwr cooling

Debris Effects in Long-Term Post-LOCA PWR Cooling

Graham WALLIS

American Nuclear Society Northeastern Meeting

October 23 2013


Short term cooling
Short-Term Cooling

  • 1960 “No need for ECCS”

  • 1971 Public Hearing

  • Creation of NRC

  • LOFT RELAP TRAC

  • 10CFR 50.46 Appendix K PCT<2200F

  • Realistic/uncertainty 95/95 confidence


Long term cooling
Long-Term Cooling

  • As important as short-term cooling

  • Water sources:

    • Inside containment

    • Outside containment

    • Recirculation

  • Fukushima

    • External water source. Hundreds of storage tanks


  • Gsi 191
    GSI-191

    • 1992 Barsebäck BWR event

    • 1996 GSI-191 “Assessment of Debris Accumulation on PWR Sump Performance”

    • Utilities required to demonstrate effective long-term cooling

    • No predictive codes

    • Prototypical tests


    Sump strainers
    Sump Strainers

    • NRC allowed strainers to be 50% blocked

    • Some were “the size of a garbage can”. 10s of square feet of surface.

    • ACRS presentation “30-50 pickup loads of debris from a large break LOCA”.

    • Utilities have installed strainers with 1000s of square feet of surface


    Functional requirements
    Functional Requirements

    • Protect downstream devices, particularly the core

    • Work for all LOCAs

    • Head Loss not to exceed allowable pump NPSH


    Protecting the core
    Protecting the Core

    • Spacers and grids. Complex shapes with small spaces may trap particles and fibers.

    • Tests desirable before designing strainers.

    • Tests are still underway after installing strainers.


    Loca debris
    LOCA Debris

    • Fiberglass. Wide range of lengths.

    • Particles. Paints, coatings, insulation (CalSil), latent debris.

    • Chemicals. Hot acidic jet. Long residence in sump at high pH. AlOOH.


    Comparison with short term cooling
    Comparison with Short-term Cooling

    • Because of the variety of debris constituents the development of a knowledge base and predictive techniques differs from the short-term case in which the medium was water alone.

    • Relating head loss and bypass tests to reality is tenuous and risky.

    • Numerous surprises and anomalous results from tests.


    Effects on head loss and bypass
    Effects on Head Loss and Bypass

    • Fiberglass and CalSil prepared in blenders.

      • Specifying amounts is inadequate. Size matters. More may be better.

      • Size spectra. Micron-sized particles.


    Some effects
    Some Effects

    • Flow history

    • Arrival sequence

    • Sump, Pumps

    • Surrogates


    Tests
    Tests

    • Should be realistic. Uncertain what may be “conservative”.

    • Prototypical tests

    • Use of single module (fuel assembly) tests to predict multi-module (core) performance


    Alternative approaches
    Alternative approaches

    • Change injection location

    • Backflushing

    • Bypass or control rod flow paths

    • Other, such as removing all fiberglass and CalSil

    • Risk-inform using PRA?


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