october 25-27, th International QUENCH Workshop 1 Top Flooding Experiments and Modeling Estelle Brunet-Thibault (EDF), Serge Marguet (EDF)

october 25-27, th International QUENCH Workshop 2 1 Top Flooding Phenomena

october 25-27, th International QUENCH Workshop 3 Hot leg injection In BWR quenching ring in upper plenum internals 1.1Scope of the top flooding physics in PWR Condensation in steam generator tubes

october 25-27, th International QUENCH Workshop 4 1.2Flooding 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.

october 25-27, th International QUENCH Workshop 5 1.2Counter Current Flow Limitation The phenomena Vertical : Horizontal :

october 25-27, th International QUENCH Workshop 6 2 Top Flooding Experiments

october 25-27, th International QUENCH Workshop 7 2.1ECCHO 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 mm Hydraulic diameter : 8 mm 33% reduction compared to PWR geometry

october 25-27, th International QUENCH Workshop 8 2.1ECCHO 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

october 25-27, th International QUENCH Workshop 9 2.1ECCHO 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

october 25-27, th International QUENCH Workshop 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

october 25-27, th International QUENCH Workshop 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

october 25-27, th International QUENCH Workshop 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

october 25-27, th International QUENCH Workshop PARAMETER (1/2) Flooding experiments at LUCH Institute (Russia) Sources: Presentation on 8 th 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 : m Tungsten heater elements Hexahedron shroud ZrO2 insulation

october 25-27, th International QUENCH Workshop 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

october 25-27, th International QUENCH Workshop 15 3 Top Flooding Modeling

october 25-27, th International QUENCH Workshop 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

october 25-27, th International QUENCH Workshop 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

october 25-27, th International QUENCH Workshop 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

october 25-27, th International QUENCH Workshop 19 4 Conclusion

october 25-27, th International QUENCH Workshop 20 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