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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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