October 25-27, 2005 11th International QUENCH Workshop 1 Top Flooding Experiments and Modeling...
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Transcript of October 25-27, 2005 11th International QUENCH Workshop 1 Top Flooding Experiments and Modeling...
october 25-27, 2005 11th International QUENCH Workshop1
Top Flooding Experiments and Modeling
Estelle Brunet-Thibault (EDF), Serge Marguet (EDF)
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1
Top Flooding Phenomena
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• Hot leg injection
• In BWR quenching ring in upper plenum internals
1.1 Scope of the top flooding physics in PWR
• Condensation in steam generator tubes
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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.
Bottom inlet water
Lower quench front
Upper quench front
Fuel rods
Single phase liquid
Single phase liquid
Nucleate Boiling
Transition boiling
Film boiling
Inverted annular flow
Dispersed flow
Single phase steam
Water annular downflow with dispersed steam upflow
Liquid film drying out
Top inlet water
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1.2 Counter Current Flow Limitation
① ② ③ ④ ⑤ ⑥ ⑦
Water inlet
Water outlet
Steam inlet
Water inlet
Steam inlet
Water inlet
Steam inlet
Water inlet ② ③ ①
The phenomena
Vertical :
Horizontal :
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2
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
• 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
Test matrix
• 49 bottom flooding tests• 4 top flooding tests• 16 combined injection
flooding tests
Measured variables
• Inner cladding temperature of heated rods• Fluid temperature• Pressure• Water injected flow rates• Electrical power
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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
respectivelyTest 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 occurscompletely without delay
• Water breakthrough occurs in frontof the injecting hot legs
• Rate and area of water breakthroughincrease 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 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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3
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 :
L is correlated on the basis of PERICLES and REWETT II experiments
5,0
G
GL
Vcr
gL
v
338,17,6 HDL
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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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4
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