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HTGR Safety Analysis and Tests in the U.S.

HTGR Safety Analysis and Tests in the U.S. Syd Ball Oak Ridge National Laboratory – USA IAEA Workshop on HTGR Safety & Market Potential Beijing, China September 27–30, 2004. Safety Testing on U.S. HTGRs was “Limited”.

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HTGR Safety Analysis and Tests in the U.S.

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  1. HTGR Safety Analysis and Tests in the U.S. Syd Ball Oak Ridge National Laboratory – USA IAEA Workshop on HTGR Safety & Market Potential Beijing, China September 27–30, 2004

  2. Safety Testing on U.S. HTGRs was “Limited” • U.S. has had no “big” HTGR experiments since Peach Bottom-1 and Fort St. Vrain • Peach Bottom: Fuel performance & fission product release-transport data (normal operation) • FSV: Reactivity transient tests (planned); several loss of forced circulation (LOFC) “tests” (unplanned)

  3. FSV Rod-Jog Tests Showed Point Kinetics Model to be Adequate

  4. Comparison of Nuclear and Physical Dimensions Relative Physical Dimensions Relative Nuclear Dimensions GT-MHR 600 MW(t) LWR 3000 MW(t) GT-MHR 600 MW(t) LWR 3000 MW(t) M-274(30) 8-21-01

  5. GRSAC – Graphite Reactor Severe Accident Code • GRSAC based on ~30 years of development at ORNL • Sponsored by NRC/DOE — (ORECA/MORECA codes) • Detailed accident modeling for gas-cooled reactor system • 3-D core thermal hydraulics (~3000 nodes) • Optional neutronics (point kinetics) for ATWS accidents • Graphite (and metal fuel/clad) oxidation model options • Fuel failure & fission product release options; can give input to a Puff weather code (HPAC) • Adaptations to GT-MHR & PBMR • Extensive validation vs. other codes & experiments • User-friendly model building • Interactive screens for inputting design data, output graphics • Smart front end input checking; on-line help, documentation • Fast run times (~ 8000 X real time for non-ATWS accidents on PC)

  6. Example PBMR Pressurized LOFC + ATWS

  7. MORECA Code: MHTGR PLOFC-ATWS with Blower Restart (SCS @ 25%) After 3 Days Shows Effect of Selective Undercooling

  8. FSV LOFC Accidents: Good V&V

  9. The Air Ingress Accident: Oxidation Occurs Mostly in the Bottom Reflector (KFA Experiment)

  10. GRSAC: PBMR Air Ingress with Single Break

  11. MHTGR Air Ingress Accidents – Conclusions • Core oxidation is limited even for VERY low probability accidents: • Single & double break scenarios, ~low rates • Core flow resistance is limiting • For underground silos, available oxygen would be limited (air-cooled RCCS??) • Oxidation rate equations determine where, not how much, graphite is oxidized; some fission product release?

  12. Conclusions • Core T/H models have considerable V&V support • Point kinetics probably valid for “mild” ATWS transients (? For VERY tall cores) • Selective undercooling a danger in ATWS • Air ingress accidents VERY unlikely, & not show-stoppers, (probably)

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