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Accident Management Issues within the ARTIST Project

Accident Management Issues within the ARTIST Project S. Güntay, A. Dehbi , D. Suckow, J. Birchley Laboratory for Thermal-Hydraulics Paul Scherrer Institut Villigen, Switzerland OECD Workshop o n the Implementation of Severe Accident Management Measures Villigen , Switzerland

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Accident Management Issues within the ARTIST Project

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  1. Accident Management Issues within the ARTIST Project S. Güntay, A. Dehbi, D. Suckow, J. Birchley Laboratory for Thermal-Hydraulics Paul Scherrer Institut Villigen, Switzerland OECD Workshop on the Implementation of Severe Accident Management Measures Villigen, Switzerland September 13, 2001

  2. Motivation behind ARTIST Project • ARTIST: Aerosol Trapping in Steam Generator • No credit given for FP retention in secondary side of a SG. • Up to now: only one large scale SGTR experiment at Westinghouse: droplet carryover in DBA-type accident. • Theoretical & laboratory-scale separate effect experiments: evidence of high aerosol removal in SGTR due to: • Turbulent deposition inside ruptured tube • Inertial & turbulent impaction on secondary structures • Thermophoresis between hot gas and colder walls • Condensation-diffusiophoresis in water pool

  3. Location DF Uncertainty Inside 0.3 m tube  3 Not known  Inside 1 m tube  10  Not known  In SG break stage  10-60  Not known  In SG far field bundle  3-10  Not known  Separator  Not known  Not known  Dryer  Not known  Not known  Flooded bundle, 4 m  20  50% Expected DF‘s according to Available Simple Models and Experiments

  4. Scaling of SG Bundle Size using CFD • Computational Fluid Dynamics (CFD) simulations conducted to: • Estimate momentum dissipation near break • Decide on ARTIST bundle size (large enough number of tubes & economically feasible) • Simulation conducted with 3 types of breaks (fish-mouth, axisymmetric) • Results: • Velocity drops by > 1 order of magnitude after 5 tube rows • Thus: momentum dissipation and aerosol removal in vicinity of break can be reproduced in ARTIST 1 to 1. • Pictures(1,2)

  5. Main Geometric Parameters in ARTIST Parameter Unit BeznauARTIST Number of tubes -3238 (U tube) 264(staight) Number of dryers - 12 1 Number of separators- 12 1 Max. tube lengthm9.0 3.8 Tube IDmm16.7 16.7 Surface/volume ratiom2/m3102.2 87.2 Porosity- 0.67 0.71

  6. ARTIST Consortium Experiments • ARTIST: International project • Running time: 2003-2007 • Many potential partners: NRC, AVN, IPSN, FRAMATOME-ANP, CSN, HSK, Skidpower, etc. • 7 Phases, addressing fission product retention in • Severe accidents (aerosols) • DBA (droplets)

  7. ARTIST Consortium (cont‘d) • Phase I: In-tube aerosol retention.Sonic flows. Velocities in tube: 200-300 m/s. • Phase II: Aerosol retention in bundle break stage, dry conditions. Sonic flows. Velocities at exit of break: 200-300 m/s • Phase III: Retention in bundle far-field, dry conditions. Impaction & thermophoresis. Low velocities: 0.1-1 m/s. • Phase IV: Aerosol retention in separator & dryer. Small velocities, less than 1 m/s.

  8. ARTIST Consortium (cont‘d) • Phase V: Aerosol retention in flooded bundle. • Phase VI: Droplet retention in separator & dryer. DBA-type experiment. • Phase VII: Integral tests. Retention in the whole SG

  9. Selected SAM Issues in ARTIST • ARTIST facility also suitable for particular AM issues • Two sets of issues identified so far: • Impact of water level on droplet formation at the water pool surface (size, flux of droplet flow) • Potential for more accurate determination of • Break location • Water level in the SG.

  10. Droplet Generation at Pool Surface • AM in SGTR involves flooding SG to scrub aerosols • Gas bubbling in SG pool creates droplet flow  new source of release • Retention in separator & dryer depends on droplet inertia  importance of droplet size • Droplet size, flux determined by flow regime upstream of water surface • Turbulent flow  large drops  easier to retain • Bubbly flow  small drops  harder to retain • Aerosol vs. droplet retention? conflicting goals. Need for optimization.

  11. Droplet Generation at Pool Surface (cont‘d) • With high water level: • Bubbly flow at surface • small bubbles • small droplets • Net effects: • High aerosol retention in pool • High droplet source to separator and dryer Aerosol Droplet Gas

  12. Droplet Generation at Pool Surface (cont‘d) • With low water level • Turbulent gas flowat surface • Large bubbles • Large droplets • Net effects: • Low aerosol retention in pool • Low droplet source to separator and dryer Aerosol Droplet Gas

  13. Droplet Generation at Pool Surface (cont‘d) • Proposed experiment: • Determine drop size & flux as function of: • Water level • Gas flow rate • Determine effect of support plate on droplet size & flux • Main objective of experiment: characterize optimum flooding level which minimizes source due to: • Aerosols • Droplets

  14. Break & Water Level Determination • Current practice: following SGTR, flooding up to 2/3 of separator (assumption: break at U bend, for lack of better guess) • Level estimated by wide-range Dp measurement of collapsed level • Uncertainty of 1 m on water level. Large. Need to preclude overfilling with potential leakage through SRV • Investigations in ARTIST proposed onfollowingtopics (related): • Determination of break level • Reduction in water level uncertainty

  15. Break & Water Level Determination (cont‘n) • Proposed experiment: • Gas discharge from a break in ARTIST • Vary: break location, flow rate, water level • Pressure measurement taken along flooded bundle • Determine correlation between break location & Dp profile • Once correlation between break location & Dp is found, correlate water level in the bundle versus: • Break flow rate • Break location • Collapsed water level • Objective of experiment: reduce uncertainty on water level estimation.

  16. Summary • ARTIST: wide-ranging project which addresses key safety issues in SGTR • Strong international interest and participation • ARTIST-Consortium experiments (2003-2007): 7 phase project, dealing with aerosol/droplet retention. Separate effects & integral tests. • Possibility to use ARTIST for further AM tests. Potential test matrix proposes investigation in two directions: • Determination of optimum flooding level to minimize source due to aerosol+ droplets • Lowering uncertainty on water level estimation in SGTR events

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