Transcript Top Flooding Experiments and Modeling Estelle Brunet-Thibault (EDF), Serge Marguet (EDF) october 25-27, 2005 11th International QUENCH Workshop.

Top Flooding Experiments and
Modeling
Estelle Brunet-Thibault (EDF), Serge Marguet (EDF)
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Top Flooding Phenomena
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1.1 Scope of the top flooding physics in PWR
• Hot leg injection
• Condensation in steam generator tubes
• In BWR quenching ring in upper plenum internals
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1.2 Flooding Patterns
Two quench fronts and two flooding
patterns
Co-current flow
• Co-current flow pattern similar to
bottom flooding
Counter-current flow
• Liquid single phase
• Annular counter-current flow : water
film and dispersed steam
The location of the drying point of the
water film is needed to consider the sharp
change in the heat transfer between the
region of dry and wetted wall and as a
consequence to get the steep temperature
decrease during quenching.
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1.2 Counter Current Flow Limitation
The phenomena
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Horizontal :
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Top Flooding Experiments
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2.1 ECCHO B – PERICLES (1/3)
Flooding experiments at CEA Grenoble (France – ended 1991)
2 tests facilities (Nuclear technology vol.107)
• ECCHO B
 37 rods
 Non heated shroud
• PERICLES
 127 rods
 Heated shroud
Geometry RSM1.1
• Triangular pitch 12.23 mm
• Hydraulic diameter : 8 mm 33% reduction compared to PWR geometry
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2.1 ECCHO B – PERICLES (2/3)
Flooding experiments at CEA Grenoble (France – ended 1991)
Test characteristics
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Pressure : 1, 2, 2.3 and 4 bars
Initial temperature : 300 and 600°C
Injected flow rates : 3.6, 5.4, 8.1 g.s-1.cm-2
Stainless steel cladding
Length of heated rods : 3.6 m
Measured variables
Test matrix
• 49 bottom flooding tests
• 4 top flooding tests
• 16 combined injection
flooding tests
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Inner cladding temperature of heated rods
Fluid temperature
Pressure
Water injected flow rates
Electrical power
11th International QUENCH Workshop
2.1 ECCHO B – PERICLES (3/3)
Flooding experiments at CEA Grenoble (France – ended 1991)
Findings
• A combined top/bottom injection does not significantly improve the
cooling efficiency due to high vapor velocities.
• Counter-current flow rapidly limited
Observations
• The tests are not sufficiently prototypics to have conclusion for
power plant applications
 Pressure too low
 The geometry is not a characteristic PWR geometry
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2.2 UPTF experiments (1/3)
UPTF Flooding experiments (Germany – ended 1991)
Description (Nuclear Engineering and Design 133)
• Full-scale (1:1) representation of :
 Upper plenum including internals
 Downcomer
 Four connected loops
• Exact representation of :
 Core barrel including core by-pass
 Upper end-box and upper part of
fuel element (0,8 m)
• ECC injection into :
 4 cold legs
 4 hot legs
 Downcomer at two regions
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2.2 UPTF experiments (2/3)
UPTF Flooding experiments (Germany – ended 1991)
Description
• Core simulated by means of controlled steam and water injection supplied
from external sources
• Reactor coolant pumps and steam generators replaced by simulators
• Breaks of variables sizes can be simulated in the hot and in the cold leg
respectively
Test characteristics
• Primary system pressure : 20 bars
• Primary system temperature : 485 K
• ECC injection
 50 to 600 kg.s-1 for each hot leg injection port
 50 to 1100 kg.s-1 for each cold leg injection port
• Onset of flooding at 10.5 bars
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2.2 UPTF experiments (3/3)
UPTF Flooding experiments (Germany – ended 1991)
Hot leg injection – Findings
• ECC delivery to the core occurs
completely without delay
• Water breakthrough occurs in front
of the injecting hot legs
• Rate and area of water breakthrough
increase with decreasing core
simulator steam injection
Observations
• Heterogeneous distribution of steam and water = geometry dependant
phenomenon
• Only LOCA scenarios
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2.3 PARAMETER (1/2)
Flooding experiments at LUCH Institute (Russia)
Sources:
• Presentation on 8th CEG-SAM meeting
“Fuel assembly tests under severe accident
conditions” LUCH Institute
Description of the facility
• 19 rods
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Geometry VVER
18 heated rod,
1 central rod non heated
Zr1%Nb cladding
UO2 pellets
Heated length : 1.275 m
• Tungsten heater elements
• Hexahedron shroud
• ZrO2 insulation
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2.3 PARAMETER (2/2)
Flooding experiments at LUCH Institute (Russia)
Scenario
• Main coolant piping break with simultaneous ECCS failure
• Restoring one ECCS channel at the stage of severe accident at
Tclad > 2250K
• The core water flooding from top and bottom with total flow rate of
200 kg.s-1
Advantages
• Severe accident scenario
 Cladding temperature
 Water flow rate
• Prototypics rods
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Top Flooding Modeling
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3.1 Top flooding modeling in CATHARE (1/2)
General description
• The model assumes a wetted wall with
 A descending liquid film upstream of the quench front
 A steep wall temperature gradient in the quench front region
 A hot dry wall downstream of the quench front
Characteristics (1/2)
• This model takes into account :
 Nucleate boiling in the descending film upstream of the quench
front
 Critical heat flux at the quench front
 Transition boiling immediately downstream of the quench front
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3.1 Top flooding modeling in CATHARE (2/2)
Characteristics (2/2)
• This model takes into account also :
 Heat transfer to droplets sputtered off the film in the quench front region
 Dispersed flow film boiling and wall-to-vapour heat transfer further
downstream of the quench front
Determination of the quench front velocity
• Application of a local CCFL criterion of the Wallis type at the upper quench
front with the critical vapour velocity given by :
vVcr 
 gL   L   G  
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G
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0 ,5
L  6 ,7 D H
1 , 338
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L is correlated on the basis of PERICLES and REWETT II experiments
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3.2 Top flooding modeling in ATHLET-CD
These information are kindly transmitted by GRS (Christine Bals)
ATHLET quench front model
• Determination of the upper quench front velocity
 Yamanouchi correlation
(only valid for vertical geometries)
 Calculation of the Leidenfrost temperature with Schröder-Richter
approximation
 Validation of this model on FLECHT, FEBA, LOFT, SCTF and CCTF
experiments
ATHLET drift flux model
• Determination of the amount of liquid available for top quenching
 Parameters of this model are influenced by UPTF data concerning CCFL
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Conclusion
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CONCLUSION
The aim of our study
• Elaboration of a severe accident top flooding model integrable in
ASTEC and in MAAP4 including:
 A model to determine the amount of water available for core
quenching
 A model to calculate heat transfer between top down flow and
upper internals
 A model to calculate heat transfer in the core upstream the upper
quench front
• Validation of the top flooding model
 PARAMETER top and bottom flooding experiment
 PERICLES top and bottom flooding experiments
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