Status and Future Challenges of CFD
for Liquid Metal Cooled Reactors
IAEA Fast Reactor Conference 2013
Paris, France
5 March 2013
Ferry Roelofs
V.R. Gopala
K. Van Tichelen
X. Cheng
E. Merzari
W.D. Pointer
2 Paris • 5 March 2013
Contents
• Introduction
• Computational Fluid Dynamics
• Thermal-Hydraulics Challenges in Design and Safety
• Liquid Metal Turbulence
• Core Thermal Hydraulics
• Pool Thermal Hydraulics
• System Dynamics
• Summary
• Acknowledgement
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Introduction Background
• Nuclear power plays and probably will play
important role in energy production
• Large role is attributed world-wide to fast
reactors
• Thermal-hydraulics is considered as key
issue
– Overview by Denis Tenchine in NE&D (2010)
– Overview by K. Velusamy (2010)
– Many subjects involve application of CFD
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Computational Fluid Dynamics
Computational Fluid Dynamics
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approximation
ph
ys
ics
co
mp
ute
r p
ow
er
DNS
LES
Hybrid
RANS/LES
(U)RANS
calculation
DNS LES Hybrid (U)RANS
System Thermal
Hydraulics
STH
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Thermal-Hydraulics Challenges in
Nuclear Design and Safety
1
2 3
4 3
TH Challenges in Design and Safety
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1
2
3
4
Core
Reactor Vessel
Heat Transfer System
Heat Transport System
1
TH Challenges in Design and Safety Core
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1 Core
Levels:
- Complete Core
- Fuel Assembly
- Subchannel
- Molten Core
2
TH Challenges in Design and Safety Reactor Vessel / Pool
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2 Reactor Vessel
- Core outlet region
- Temperature stratification &
fluctuations
- Gas entrainment
- Fission product transport
- Forced-natural convection
3 3
TH Challenges in Design and Safety Heat Transfer System
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3 Heat Transfer System
- Efficiency
- Integrity
- Correlations
4
TH Challenges in Design and Safety Heat Transport System
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4 Heat Transport System
- 3D effects
- Coupling STH-CFD
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Liquid Metal Thermal-hydraulics
Liquid Metal Thermal-Hydraulics Heat transfer for low Prandtl number fluids
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• Issue with Low Prandtl number fluids
– Existing (U)RANS engineering turbulence
models all use Reynolds analogy for
coupling temperature and velocity fields
– Not valid for fluids with low Prandtl
numbers (e.g. liquid metals)
source: R. Stieglitz (KIT)
Viscous boundary layer
Thermal boundary layer
Ratio thermal/viscous
Reynolds analogy th=
Liquid Metal Thermal-Hydraulics Heat transfer for low Prandtl number fluids
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Velocity
Temperature (Pr = 1) Temperature (Pr = 0.01)
Field Scales Boundary
Layer
Velocity Small Thin
Temperature (Pr = 1) Small Thin
Temperature (Pr = 0.01) Large Thick
Liquid Metal Thermal-Hydraulics Improvement of (RANS) models
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• Implemented in cooperation between CD-adapco, NRG and model developer
Sasa Kenjeres (TU Delft) in STAR-CCM+ β-version
• Challenge: Derive a model for use in all flow regimes simultaneously
2
3210 i
u
j
ij
u
j
ji
uu
i gCx
UuC
x
TuuCCu
AHFM: Kenjeres &
Hanjalic (2005)
Flow
Regime Gr(Pr, Re)
(velocity) Heat transfer
Existing
Models
AHFM
Kenjeres
2000
AHFM
Kenjeres
2005
Natural Low Conduction &
Buoyancy -
+ (air)
- (LM)
+ (air)
+ (LM)
Mixed Intermediate Mixed - - +
Forced High Convection o/+ - +
stability
Careful selection
of model constants
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Core Thermal-hydraulics
Core Thermal-Hydraulics Subchannel
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• 7 pin rod bundle – Code independence (STAR-CCM+ vs. OpenFOAM)
– Application of various RANS turbulence models confirms negligible influence
• 19 pin rod bundle – Grid independence (1M vs 5M vs 9M)
• Validation (Challenge) – JAEA experiments (large uncertainties → limited
validation)
– ANL reference 7 pin LES benchmark (ANL-SCK-NRG cooperation starting 2013)
– NRG reference 1 pin LES (under preparation)
– Experiments in NACIE and KALLA loops (2013-2014)
7 pin bundle LES (ANL)
Single pin LES preparation (NRG)
19 pin RANS (NRG)
Core Thermal-Hydraulics Fuel Assembly
• Numerical evaluation of performance of
spacer designs
– Pressure drop
– Clad temperatures
– Local velocities
– Cross flow
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ALFRED FA (SRS)
Evaluation of spacer performance (NRG)
Core Thermal-Hydraulics Fuel Assembly
• LES reference data (ANL)
– 7 Pin Bundle
– 19 Pin Bundle
– 37 Pin Bundle
– 217 Pin Bundle
• Validation of RANS and low
resolution approaches
– Pressure drop
• Improvement of correlations
• Extending applicability range of
correlations
– Velocity and it’s fluctuations
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217 pin sodium bundle LES (ANL)
Core Thermal-Hydraulics Fuel Assembly
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Approach Traditional CFD LRGR CFD
Mesh
Solve All (Flow, bulk turbulence,
boundary layers,
secondary flows)
Main flow
characteristicts
Bulk turbulence
Sub Grid Model To consider
Core Thermal-Hydraulics Complete Core
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Complete geometry
Identify representative
block within complete
geometry
Section of geometry
Setup of numerical grid for
representative block
Detailed CFD-simulation
of representative block
Extraction of CG-Forces
employing CFD results
Complete geometry
Setup coarse mesh for
complete geometry
Simulation of complete
geometry
employing CGCFD
Parameterization
of CG-Forces
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Pool Thermal-hydraulics
Pool Thermal-Hydraulics Fundamental Validation
• Triple Jet (Nam & Kim, 2004)
– LES & RANS
• Double Jet: MAX facility (ANL)
– Design support by LES
– Validate LES and RANS with
experimental results
23
LES of Triple parallel jet
experiments by Nam & Kim (2004)
MAX facility and design support (ANL)
Pool Thermal-Hydraulics Integral Simulation
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Democritos Water Mock-up
(VKI)
MYRRHA Design
(SCK)
ESCAPE LBE Mock-up
(SCK) Scaling simulations
Full scale – velocity scale – Froude scale
• Simulation of integral pool system
– Challenge: Validation with experimental campaign (water and
liquid metal)
Pool Thermal-Hydraulics Gas Entrainment
• Determination of flow patterns in SFR upper
plenum to analyse gas entrainment risk
• From URANS to LES modeling approaches
• From single phase to multiphase
• Modeling core outlet and large components
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Multiphase LES in TRIO-U (Tenchine, 2010)
URANS (NRG)
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System Dynamics
System Dynamics
• Code Coupling
– ATHLET – OpenFOAM (KIT)
– Phenix natural convection test
– Pool in OpenFOAM
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ATHLET nodalization and 3D pool snapshot from OpenFOAM (KIT)
System Dynamics
• Code Coupling
– CATHARE – TRIO_U (CEA)
– Phenix natural convection test
– Dedicated post-processing tools enabling 3D visualization
(using 3D glasses) of sodium flow patterns in reactor pool
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Summary
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Summary & Conclusions
• Status of CFD developments and future challenges:
– Liquid metal turbulence
• Heat transport modelling for RANS and LES
• Thermal fluctuation prediction for thermal fatigue evaluation
• Flow induced vibrations of e.g. a fuel pin
– Core thermal hydraulics
• Wire wrap fuel assembly simulation and validation
• Low resolution CFD modelling of a fuel assembly to assess blockage scenarios
• Coarse Grid CFD development to allow modelling a complete core
– Pool thermal hydraulics
• Fundamental validation using separate effect facilities, e.g. multiple jets
• Pool modelling validation using prototypical scaled down facilities
• Gas entrainment modelling and validation
• Seismic evaluations including liquid metal sloshing
– System dynamics.
• Coupling of STH and CFD
Acknowledgements
• Colleagues at
– NRG
– SCK•CEN
– KIT
– ANL
• Denis Tenchine and his colleagues at CEA!
31 Paris • 5 March 2013
