WP2.3: Boiling Water Reactor Thermal- Hydraulics H. Anglart, D. Caraghiaur, D. Lakehal, J. Pérez, V. Tanskanen, M. Ilvonen
BWR Thermal-hydraulic issues CFD Eulerian/Eulerian approach (KTH) Annular flow /dryout Subchannel code CATHARE-3 (VTT) Core transient simulations using NEPTUNE_CFD code (KIT) Steam injection /condensation Various simulation approaches: URANS using NEPTUNE_CFD (LUT) DNS, LES, VLES + ITM (ASCOMP & LUT)
OBJECTIVES 1. Development of dryout modelling capability using CFD approach (KTH) mechanistic c deposition on model 3D formulation, two-fluid formulation with liquid film capability 2. CATHARE-3 simulations and validation (VTT) Validation of dryout predictions Validation of film flow predictions against KTH data 3. Validation of the NEPTUNE_CFD code (KIT) Validation against BFBT (turbine and pump trip) Calculated void compared to measurements Coupling with thermal solver Syrthes 4. Condensation modelling and validation against POOLEX (ASCOMP+LUT) Low-Re, quasi-steady interface condensation simulations High-Re, chugging interface condensation simulations
WP2.3: Boiling Water Reactor Thermal- Hydraulics Towards CFD Euler/Euler dryout capability D. Caraghiaur, KTH
Drops in annular flow (KTH) t ( s) inertia gravity t p ( gτ p τ p = + e p (0) V p (0) Discrete volume in CFD V ( t ) V )
Semi-local deposition model for CFD calculations (KTH) The drop deposits if: Drop turbulence is calculated: distance T L Vames and Hanratty (1988) v * = 0.046 2R 4 k T = Zaichik et al (2008) L 3 C 0 ε '2 τ p v p to v '2 f '2 v p 1.0 wall = 1. 0 + τ T p L
Probability of deposition (KTH) Probabilit y = experimental calculated value value
Disperse turbulence model (KTH) Inclusion of particle relaxation influence into the Reynolds stress equation exp: Jepson et al. 1989: helium-water exp: Hewitt et al. 1969: steam-water, P=70 bar LPT-DRW: Liu&Agarwal LPT-DRW: Jepson air-water present model: Liu&Agarwal present model: Jepson air-water 1 exp: Jepson et al. 1989: air-water exp: Liu&Agarwal 1970: air-olive oil LPT-DRW: Jepson helium-water LPT-DRW: Hewitt present model: Jepson helium-water present model: Hewitt 0,1 k D + 0,01 0,001001 0,0001 test of 1D model 0,00001 0,1 1 10 100 1000 10000 100000 τ + p
Conclusions on dryout CFD capability (KTH) A model for deposition applicable to CFD calculations has been formulated The model with post-processing of turbulence characteristics for drops has been compared to 4 sets of experimental data (including high pressure steam-water) It shows a good trend (better than Lagrangian tracking tested t in NURESIM)
WP2.3: Boiling Water Reactor Thermal- Hydraulics Validation of CATHARE-3 code against KTH data M. Ilvonen, VTT
CATHARE-3 simulations and validation (VTT) Description of the experiment: Liquid film flow studied by KTH Published: Adamsson & Anglart 2006 Main feature: Effect of axial power distribution (APD) on film flow Vertical heated tube, length = 3.65 m, D in = 14 mm (see upper Figure) Direct heating by electric current through the tube; APD imposed by machining i the tube 1 uniform + 3 non-uniform axial profiles (inlet, middle and outlet peaked; see lower Figure) Upward boiling flow in BWR conditions (70 bar, inlet mass flux 750 1750 kg/m 2 s) Liquid film was sucked through a porous section in wall and measured Measured: film flow rates (21 experiments), or dryout power (12 experiments)
CATHARE-3 simulations and validation (VTT) CATHARE-3 (CEA Pilot Code) relevant features: 3-field (9-equation) model: continuous liquid, continuous gas, liquid droplets Frictions between the fields, wall friction, interfacial & wall heat transfers and phase changes, mass transfers by entrainment and deposition Only the OAF (Onset of Annular Flow) transition is explicit in CATHARE-3 Entrainment in the Pilot Code: Hewitt & Govan tearing off from wave tops Ueda film bursting by bubbles due to boiling Deposition in the Pilot Code: Hewitt & Govan transverse droplet diffusion Hoyer inhibition by steam diffusion from film interface Yang et al. 2006:
CATHARE-3 simulations and validation (VTT) Simulation results for dryout experiments: 0.1 Example: Case 6, with dryout observed at outlet 0.05 Uniform APD, 1.22 MW/m 2 Inflow 1750 kg/m 2 s Upper Figure: Mass flow rates of 3 fields Dryout was not yet reached in simulation with given parameters of experiment Lower Figure: Entrainment E starts consuming the film at 0.5 m; minimum E at 3 m height Deposition D only starts at 3 m height Net entrainment E D turns negative after 3 m height, kg/s mass flow rate 0.35 0.3 0.25 02 0.2 0.15 Case 6: uni 1750 kg/m2s 1.22 MW/m2.f07; L,G,D 0 0 0.5 1 1.5 2 2.5 3 3.5 ZV (height along the heated tube, m) Green = continuous liquid film flow Red = liquid droplets flow Black = continuous vapour core flow Black circles = total mass flow rate Blue = entrainment rate E Magenta = deposition rate D Black = E - D Red = difference of droplet field flow rate
CATHARE-3 simulations and validation (VTT) Simulation results for film flow rate measurements: Example: Case 15, with measured film flow rate (appr. 20 g/s) Outlet peaked APD, 1.00 MW/m 2 Inflow 1750 kg/m 2 s Upper Figure: Mass flow rates Simulated film flow rate is reasonably good, but leaves the measured error channel around 3.5 m of tube height Lower Figure: Entrainment t E starts t consuming the film at 1.0 m; minimum E at tube outlet Deposition D only starts at 3.3 m height Net entrainment E D turns negative only after 3.5 m height, kg/s mass flow rate 0.3 0.25 0.2 015 0.15 0.1 0.05 0 Case 15: out 1750 kg/m2s 1.00 MW/m2.f07; L,G,D -0.05 0 0.5 1 1.5 2 2.5 3 3.5 ZV (height along the heated tube, m) Green = continuous liquid film Red = liquid droplets Black = continuous vapour core Black circles = total mass flow rate Blue = measured film flow rate Blue = entrainment rate E Magenta = deposition rate D Black = E - D Red = difference of droplet field flow rate
CATHARE-3 simulations and validation (VTT) Summary of findings: Dryout experiments: Low mass inflow rates are hardest to simulate. Middle and inlet peaked APDs are hardest. Film flow rate measurements: Most simulated cases have a non-monotonic film flow rate (decrease followed by increase), but measured film flow was always monotonic decreasing. Low power >> large prediction error High power >> very small errors Deposition rate has discontinuities and sharp peaks. Correlations, particularly deposition, should be studied in detail. Ultimately, one should gradually move away from use of empirical correlations and towards a more mechanistic modeling of the entrainment and deposition processes.
WP2.3: Boiling Water Reactor Thermal- Hydraulics Validation of NEPTUNE_CFD code against BFBT data J. Pérez, KIT
Validation of the Neptune_CFD (KIT) Validation of the NEPTUNE_CFD code BFBT benchmark is used to validate two phase flow models of Neptune CFD 1.0.8. two scenarios are simulated: A turbine trip without bypass and a recirculation pump trip. Experimental void fraction measurement are compared against the simulations at three different axial levels. NEPTUNE_CFD is coupled with thermal solver Syrthes improving local temperatures prediction, specially in the near wall region.
Validation of the Neptune_CFD (KIT) NUPEC BWR full Size fine mesh bundle test benchmark Void distribution measurements. Experiment number 4102/001-009 BWR full sized fuel assembly Flow rate 35 to 55 t/h Power from 2.5 to 6.5 MW Heated length 3.7(m), total 3.95(m) Constant nt axial power shape Pressure 7-8 Mpa Constant inlet temp, 552 (K) External ø of rods: 12.2mm Radial power shape distribution Void fraction measured at 3 levels Sampling frequency: 50 Hz Measurements of the averaged void at 3 different axial levels: 0.68 m, 1.7 m and 2.73 m Local void fraction distribution in the domain:
Validation of the Neptune_CFD (KIT) NUPEC BWR full Size fine mesh bundle test benchmark Experimental conditions (Turbine Trip + Pump Trip) MPa 8,2 8,0 7,8 76 7,6 7,4 7,2 7,0 6,8 60 PumpTrip 50 Turbine Trip 40 30 10 0 0 20 Time (s). 40 60 t/h 20 TurbineTrip PumpTrip 0 10 20 30 40 50 60 Time (s). MW 7,0 6,0 50 5,0 4,0 3,0 2,0 1,0 0,0 PumpTrip TurbineTrip 0 20 40 60 Time (s).
Validation of the Neptune_CFD (KIT) Neptune_CFD models Generalities Eulerian approach, 2 phases with 3 equations for each phase (momentum mass and energy) RANS simulation. First order upwind scheme for pressure and energy Second order r scheme for velocities and volume fractions. K-ε for the liquid phase No turbulence model for the gas phase. (Compressible) q li = C C ki li ( T T ) sat Nul k = d Nu = 2 + 0.6 Re l 1/ 2 Pr k 1/ 3 Heat exchange models: Wall heat exchange: Kurul and Podowski extension (4 fluxes model by J.Lavieville). Liquid properties controlled by Cathare tables Heat transfer term for the liquid-interphase: Ranz-Marshall / Astrid / Flashing Gas phase energy controlled by a constant t time scale returning to saturation. y + = 250 for the liquid characteristics at the wall. SYRTHES code is applied to solve the conjugated heat transfer at the wall. q wall q vi = A i α ρ t v C pv ( T T ) sat ( qc + qq + qe ) + ( f ) qv = fα1 1 α1 c T 2
Validation of the Neptune_CFD (KIT) Neptune_CFD models Bubbly flow regime Interfacial area equation for bubble diameters ( two different minimum bubble ø, 0.15mm am 0.1 mm ) Break up and coalescence from W.Yao and C.Morel Interfacial momentum transfer: Drag force: Ishii correlation Lift force by Tomiyama Wall lubrication by Antal Turbulent dispersion force by Lance & Lopez de Bertodano Added mass force by Zuber Ai + t ( A V ) i 2 v 2 Ai = αρ Γ 3 v C v N v NUC COA BRK [ φ + φ φ ] α +12 π n n + A i k D k A i n + Γ Dv ρv α Dt α d = 6 Sauter mean diameter AM k L k TD k M = M + M + M + M + M WL k
Validation of the Neptune_CFD (KIT) Selected results: Avg. void fraction at 3 axial levels (Turbine Trip) Neptune_CFD Neptune_CFD / Syrthes
Validation of the Neptune_CFD (KIT) Selected results: Avg. void fraction at 3 axial levels (Pump Trip)
Validation of the Neptune_CFD (KIT) Selected results: Local steam and water temperatures (Turbine Trip) Near wall region:
Validation of the Neptune_CFD (KIT) Selected results: Local steam and water temperatures (Pump Trip) In the bulk the water and steam temp. remain at saturation In the near wall region the steam is superheated The excesive steam overheat can be controled by decreasing the time scale returning to saturation Water Temp. in the near wall region
WP2.3: Boiling Water Reactor Thermal- Hydraulics Condensation modelling and validation against POOLEX data V. Tanskanen, LUT D. Lakehal, ASCOMP
Condensation modelling in suppression pools (LUT/ASCOMP) During the project, two condensation modes of suppression pools were simulated by using the direct contact condensation (DCC) models of separated flow. These models were the same as used within the PTS context of the NURISP project. Low-Re, quasi-steady interface condensation simulations were carried out by using the DCC models of Hughes & Duffey (1991), Lakehal (2008), Coste- STB-31 exp. Laviéville (2009), and Coste (2004). STB-28 exp. Pattern - High-Re, chugging interface recognition condensation simulations were carried out by using the DCC models of Hughes & Duffey (1991), Lakehal (2008), and Coste-Laviéville (2009). - NEPTUNE_CFD and TransAT CFD codes were used as solvers. - A Pattern recognition procedure was employed to obtain comparable quantitative data from the chugging experiments.
DCC on the quasi-steady steam/water interface (LUT/ASCOMP) NEPTUNE_CFD TransAT Light grey envelope: Measurement uncertainty due to possible non-condensable gases Grey envelope: Base measurement uncertainty In the low-re condensation case, the DCC model of Lakehal 2008 g gives a condensation rate prediction which is near to the measured values. Other models tend to overestimate the DCC rate. The results of NEPTUNE_CFD and TransAT are similar.
DCC during chugging steam/water interface (LUT/ASCOMP) In the high-re condensation case, the DCC model of Hughes & Duffey yields realistic bubble size distribution and chugging frequency. Chugging cases have been simulated by using the NEPTUNE_CFD code. Af few TransAT simulations have been started. Exp. STB-28-4 Bubble size distribution Experiment STB-28-4 2D-axi. Hughes- Duffey, Nept. 3D,Hughes-Duffey, Nept. Chugging frequency Exp. STB- 28-4 1.07 Hz 0.63 Hz 2D-axi axi. Hughes- Duffey, Nept.
The NEPTUNE_CFD and TransAT simulations of the chugging condensation mode have revealed new information of the significant effect of the pool turbulence (mixing) on the condensation rate i.e. on the violence of chugging. It is likely that LEIS simulations, long 3D URANS simulations, and experiments with turbulence and/or velocity field measurements could provide crucial results for the best-estimatesolution of this challenging High shear condensation problem. DCC during chugging steam/water interface (LUT/ASCOMP) 2D-axi,TransAT Turbulence kinetic energy, 3D, NEPTUNE_CFD High shear High bulk turbule nce Turbulence kinetic energy, 2D-axi,TransAT
CONCLUSIONS 1. A new deposition model for Eulerian/Eulerial framework has been developed, allowing for: 3D, general formulation on development towards mechanistic dryout capability in CFD Eulerian/Eulerian codes 2. CATHARE-3 annular flow predictions has been validated against KTH film measurement data Reasonable agreement for high powers; difficulties for low flows Areas for further improvements of predictions have been identified 3. Validation of the NEPTUNE_CFD code against BFBT has been performed Calculated void compared to measurements and good agreement has been found Coupling with thermal solver Syrthes tested to improve wall temperature predictions 4. Condensation modelling and validation against POOLEX Low-Re, quasi-steady interface condensation best predicted with the Lakehal model High-Re, chugging g frequency and bubble size best predicted with the Hughes&Duffey model.