CFD for Containment Analyses Hydrogen Management in LWRs
Transcript of CFD for Containment Analyses Hydrogen Management in LWRs
CFD for Containment AnalysesHydrogen Management in LWRs
JAHRESTAGUNG KERNTECHNIKTopical Session, May 19, 2011
Berliner Congress Center
Dirk C. [email protected]
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Contents
� Introduction:• NRG• Hydrogen Risk in LWRs
� CFD for Hydrogen Management:• NRG Hydrogen Distribution Analyses
� CFD Requirements & Guidelines
• NRG Hydrogen Combustion Analyses
� Summary
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Established 1998
Staff ~340
Locations Petten & Arnhem
� NRG offers consultancy services in:
• in-core fuel management• in-service inspections• project services • safety assessment and licensing
� NRG is one of largest suppliers of medical isotopes worldwide
� more info on http://www.nrg.eu
Introduction – NRG
310 km to Hannover
120 km to Essen
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Introduction - Hydrogen Risk in LWRs
Hydrogen is a key safety issue for water cooled rea ctors
- Large amounts of hydrogen may be generated and released in the reactor containment during a severe accident
- Hydrogen and oxygen can form a flammable or explosive gas mixture, depending on the H2-Air-Steam composition
- Hydrogen combustion/explosion may damage (safety) relevant equipment and challenge the integrity of the containment
- The potential risk of hydrogen depends on the H 2-Air-Steam composition in the containment
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Introduction - Hydrogen Risk in LWRs
For assessment of the Hydrogen Risk it is important to:
1. predict the local gas composition and local process conditions (p, T, turbulence) in the containment during a severe accident transient � H2 distribution analyses
2. predict the combustion process � H2 combustion analyses
3D
complex
For both, 3D CFD modeling is required
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CFD for Hydrogen Management
CFD model should be able to capture• distribution and mixing of H2, Air and Steam
• complex 3D phenomena : e.g. condensation, stratification, jets/plumes,
buoyancy effects, turbulent mixing, H2 combustion / explosion
• mitigation measures : e.g. recombiners, sprays, coolers
Status of CFD for Containment Analyses one decade a go
• extensive user modeling
• long computation times• reliability not demonstrated
• no quality guidelines
���� CFD modeling made a big step forward in last 10 yea rs
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Containment Analyses at NRG
� FLUENT CFD code selected for its:- excellent parallel performance
- efficient solver
- flexible meshing capabilities
� Parallel computer cluster (>400 CPUs)
� NRG developed, implemented, verified and validated specific ‘user-defined’ sub-models for:
- condensation/ evaporation on walls and in bulk- rain-out of mist
- heat transfer with walls
- diffusion and turbulent mixing- recombiners and sprays
- combustion
� Optimization of numerical schemes for speedup of calculations
CFD for Hydrogen Management
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Verification & Validation of the H 2 distribution model
Separate effect tests:- SARNET condensation benchmark
- SARNET recombiner benchmark
- SARNET-2 spray benchmark (single falling droplet)
Validation against experiments in large-scale tests facilities:- TOSQAN (7m3) � IRSN- THAI (60m3) � Becker Technologies / GRS
- MISTRA (100m3) � CEA
- PANDA (200m3) � PSI
NRG H2 Distribution Analyses
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NRG H2 Distribution Analyses
PHASE 2:4300 – 6800 s hot steam injection
Initially a N2-rich
atmosphere at
ambient condition
H2O
H2
N2PHASE 1:0 – 4300 sH2 injection
THAI-HM2 benchmark: formation and dissolution of a stratified H2-rich layer by a buoyant plume
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THAI-HM2 benchmark: formation and dissolution of a stratified H2-rich layer by a buoyant plume
CFD analysis NRG
Experiment
4760 s4300 sTHAI vessel
NRG H2 Distribution Analyses
� Good prediction of build-up and break-up of stratification� Quality Guidelines developed for mesh resolution, time step size and turbulence modeling� Solver settings are optimised to reduce calculation time
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Ho
t w
all
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steam~1.2g/s
steam/air ~4g/s
steam~12g/s
steam~1.2g/s
steam~1g/s
steam/air ~4g/s
steam/He ~2g/s
TOSQAN test ISP-47: Flow and condensation under different representative conditions
EXP vs. CFD
NRG H2 Distribution Analyses
� Correct prediction of condensation rate during different transients
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PANDA test ST1_7_2 (SETH-2):break-up/erosion of a stable helium layer by a low momentum air plume
NRG H2 Distribution Analyses
� Good a priori prediction of stratification break-up
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TOSQAN spray test T113 (SARNET):Mixing of a stable helium stratification by spray injection from a single nozzle
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NRG H2 Distribution Analyses
� Successful application of NRG spray model
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CFD Quality Assurance
� Essential Quality Requirements for Containment Anal yses:• Conservation of mass
• Mesh independent
• Time step independent
� In-house Quality Guidelines developed for:• Mesh resolution• Turbulence model/parameters
• Transient settings (time step, # iterations per time step, etc)
NRG H2 Distribution Analyses
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Interim Summary
� In-house quality guidelines and specific sub-models are developed for Containment Analyses
� NRG’s Containment modeling in FLUENT for H2 distribution/mitigation analyses is validated against the available large-scale experiments in TOSQAN (7m3), THAI (60m3), MISTRA (100m3) and PANDA (200m3)
� Reliable predictions are obtained with CFD for H2 distribution / mitigation, using the quality guidelines and sub-models developed by NRG
� Practical computing times are feasible using parallel computing and optimised numerical schemes
NRG H2 Distribution Analyses
���� 5~10 million cells are required for a typical full scale LWRcontainment (transient scenarios will take about 2 weeks on 40 CPUs)
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Combustion model implemented in FLUENT by NRG is validated against H2deflagration experiments in ENACEFF (F), THAI (D), and FLAME (USA) facility:
� Combustion process and resulting pressure loads on containment walls show a strong dependence on:
• Mesh resolution• Time step • Initial turbulence
� Experiments by Bradly, Groff and Cammarota (methane / propane –air deflagrations) confirm the strong influence of initial turbulence on deflagrations
NRG H2 Combustion Analyses
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turbulence level results in higher flame speed
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This results in the following requirements- Experimentally: the initial turbulence has to be measured- Numerically: Successive mesh size and time step refinement has
to be applied
At the moment, adequate validation of the H 2 combustion analyses is not possible , because no H2 combustion experiments are currently available where the initial turbulence is measured
NRG H2 Combustion Analyses
���� CFD analyses for H 2 management in LWRs should be focused on distribution and mitigation
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Summary
� Hydrogen management is a key severe accident issue for existing and new LWRs
� CFD analyses are an essential tool for adequate Hydrogen Management
� CFD Containment Analyses give reliable results provided that thequality guidelines are followed and valid sub-models are used
� CFD reached a level at which it can be applied in full-size plant analyses by making use of parallel computing and optimised numerical schemes
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The End
“Thanks for your attention”