cfd for containment analyses hydrogen management in lwrs
TRANSCRIPT
CFD for Containment AnalysesHydrogen Management in LWRs
JAHRESTAGUNG KERNTECHNIKTopical Session, May 19, 2011
Berliner Congress Center
Dirk C. [email protected]
Jahrestagung Kerntechnik, May 19, 2011 - Berlin 2
Contents
� Introduction:• NRG• Hydrogen Risk in LWRs
� CFD for Hydrogen Management:• NRG Hydrogen Distribution Analyses
� CFD Requirements & Guidelines
• NRG Hydrogen Combustion Analyses
� Summary
Jahrestagung Kerntechnik, May 19, 2011 - Berlin 3
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
Co
ldw
all
T (K)
inle
t
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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time (s)
volu
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eliu
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cfd - h=7.5m
cfd - h=6.9m
cfd - h=6.3m
cfd - h=5.6m
cfd - h=0.5m
exp - h=7.5m
exp - h=6.9m
exp - h=6.3m
exp - h=5.6m
exp - h=0.5m
EXP vs. CFD
helium vol%
time
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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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heliu
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cfd - 0.9mcfd - 1.9mcfd - 2.8mexp - 0.9mexp - 1.9mexp - 2.8m
EXP vs. CFDCFDTOSQAN
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
0 0.005 0.01 0.015 0.02 0.025 0.030
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Flam
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/s]
rmax 1mm
123 ���� a higher initial
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”