Status and Future Challenges of CFD for Liquid Metal Cooled Reactors IAEA Fast Reactor Conference 2013 Paris, France 5 March 2013 Ferry Roelofs roelofs@nrg.eu V.R. Gopala K. Van Tichelen X. Cheng E. Merzari W.D. Pointer
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 2
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 3
Computational Fluid Dynamics 4
physics computer power Computational Fluid Dynamics calculation DNS (U)RANS Hybrid DNS LES STH LES Hybrid RANS/LES (U)RANS System Thermal Hydraulics approximation
Thermal-Hydraulics Challenges in Nuclear Design and Safety 6
TH Challenges in Design and Safety 3 3 2 4 1 1 2 3 4 Core Reactor Vessel Heat Transfer System Heat Transport System 7
TH Challenges in Design and Safety Core 1 1 Core Levels: - Complete Core - Fuel Assembly - Subchannel - Molten Core 8
TH Challenges in Design and Safety Reactor Vessel / Pool 2 2 Reactor Vessel - Core outlet region - Temperature stratification & fluctuations - Gas entrainment - Fission product transport - Forced-natural convection 9
TH Challenges in Design and Safety Heat Transfer System 3 3 3 Heat Transfer System - Efficiency - Integrity - Correlations 10
TH Challenges in Design and Safety Heat Transport System 4 4 Heat Transport System - 3D effects - Coupling STH-CFD 11
Liquid Metal Thermal-hydraulics 12
Liquid Metal Thermal-Hydraulics Heat transfer for low Prandtl number fluids 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) Viscous boundary layer Thermal boundary layer Ratio thermal/viscous Reynolds analogy th = source: R. Stieglitz (KIT) 13
Liquid Metal Thermal-Hydraulics Heat transfer for low Prandtl number fluids Field Scales Boundary Layer Velocity Small Thin Temperature (Pr = 1) Small Thin Temperature (Pr = 0.01) Large Thick Velocity Temperature (Pr = 1) Temperature (Pr = 0.01) 14
Liquid Metal Thermal-Hydraulics Improvement of (RANS) models AHFM: Kenjeres & Hanjalic (2005) u i u u T u U i u 2 C0 C 1 uiu j C2 u j C3 gi x j x j 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 Flow Regime Gr(Pr, Re) (velocity) Heat transfer Existing Models AHFM Kenjeres 2000 AHFM Kenjeres 2005 stability Natural Low Conduction & Buoyancy - + (air) - (LM) + (air) + (LM) Mixed Intermediate Mixed - - + Forced High Convection o/+ - + Careful selection of model constants 15
Core Thermal-hydraulics 16
Core Thermal-Hydraulics Subchannel 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) 19 pin RANS (NRG) Single pin LES preparation (NRG) 7 pin bundle LES (ANL) 17
Core Thermal-Hydraulics Fuel Assembly Numerical evaluation of performance of spacer designs Pressure drop Clad temperatures Local velocities Cross flow ALFRED FA (SRS) Evaluation of spacer performance (NRG) 18
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 217 pin sodium bundle LES (ANL) 19
Core Thermal-Hydraulics Fuel Assembly 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 20
Core Thermal-Hydraulics Complete Core Complete geometry Section of geometry Complete geometry Parameterization of CG-Forces Identify representative block within complete geometry Setup of numerical grid for representative block Detailed CFD-simulation of representative block Extraction of CG-Forces employing CFD results Setup coarse mesh for complete geometry Simulation of complete geometry employing CGCFD 21
Pool Thermal-hydraulics 22
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 LES of Triple parallel jet experiments by Nam & Kim (2004) MAX facility and design support (ANL) 23
Pool Thermal-Hydraulics Integral Simulation Simulation of integral pool system Challenge: Validation with experimental campaign (water and liquid metal) MYRRHA Design (SCK) ESCAPE LBE Mock-up (SCK) Democritos Water Mock-up (VKI) Scaling simulations Full scale velocity scale Froude scale 24
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 Multiphase LES in TRIO-U (Tenchine, 2010) URANS (NRG) 25
System Dynamics 26
System Dynamics Code Coupling ATHLET OpenFOAM (KIT) Phenix natural convection test Pool in OpenFOAM ATHLET nodalization and 3D pool snapshot from OpenFOAM (KIT) 27
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 28
Summary 29
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 30
Acknowledgements Colleagues at NRG SCK CEN KIT ANL Denis Tenchine and his colleagues at CEA! 31