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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. 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

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  1. Debris Effects in Long-Term Post-LOCA PWR Cooling Graham WALLIS American Nuclear Society Northeastern Meeting October 23 2013

  2. 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

  3. Long-Term Cooling • As important as short-term cooling • Water sources: • Inside containment • Outside containment • Recirculation • Fukushima • External water source. Hundreds of storage tanks

  4. 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

  5. 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

  6. Functional Requirements • Protect downstream devices, particularly the core • Work for all LOCAs • Head Loss not to exceed allowable pump NPSH

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Some Effects • Flow history • Arrival sequence • Sump, Pumps • Surrogates

  12. Tests • Should be realistic. Uncertain what may be “conservative”. • Prototypical tests • Use of single module (fuel assembly) tests to predict multi-module (core) performance

  13. 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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