DEVELOPMENT OF COMPUTATIONAL MULTIFLUID DYNAMICS MODELS FOR NUCLEAR REACTOR APPLICATIONS

Transcription

1 DEVELOPMENT OF COMPUTATIONAL MULTIFLUID DYNAMICS MODELS FOR NUCLEAR REACTOR APPLICATIONS Henry Anglart Royal Institute of Technology, Department of Physics Division of Nuclear Reactor Technology Stocholm, Sweden SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober 2006

2 Outline of the Presentation Introduction Prospective applications of CMFD in nuclear field focus on fuel assemblies Model description Example predictions Conclusions SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

3 Introduction CMFD is used for thermal-hydraulic analyses of various parts of nuclear power plants: Reactor cores and fuel assemblies Primary systems Containment systems Analysis of fuel assemblies has large potential due to: Economical reasons (increased power) Safety reason (better estimation of thermal margins) SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

4 Typical LWR Fuel Assemblies PWR fuel assembly BWR fuel assembly Top tie plate Fuel rod Box Water cross Spacer grid Bottom tie plate SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

5 Typical Spacer Grid Spacer grid is made of plate with mm thicness. Grid height is ~30 mm, and side length ~65 mm There are usually 7-8 spacer grids along assembly full length (~3.7 m) SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

6 Thermal Hydraulic Performance of Fuel Assemblies Predictions of thermal-hydraulic performance of fuel assemblies with spacers Pressure drop Void fraction distributions Thermal margins, that is conditions when critical heat flux occurs SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

7 Design of Fuel Assemblies For design purposes, it is interesting to now the influence of geometry features on the thermal performance: Rod lattice pattern (pitch/diameter ratio, etc) Shape of sub-channels Spacer grid details (shape, mixing vanes, tabs, etc) SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

8 Four-Fluid Model Governing Equations Mass Momentum Energy ( α ρ ) t ( α ρ U ) N t + p N p ( ΓU ΓU) + = 1, + N p ( α ρ U ) = ( Γ Γ ) = 1, e ( α ρ U U ) = α µ U + ( U ) M = 1, [ ( )] T α p + α ρ g + N p ( α ) p ρ H e + ( α ρ U H α λ T) = Q + ( ΓH Γ H) + t N = 1, E = 1, SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

9 9 Turbulence Model SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober 2006 = + + = N p t t e 1, µ µ µ µ l b b b l b t lb d C U U = α ρ µ µ t C µ µ ρ 2 = Effective viscosity laminar eddy Interface-induced ( ) ( ) ( ) ( ) N N e c S t p p + Γ Γ + = + = =, 1 1, α µ α ρ α ρ α U ( ) ( ) ( ) ( ) N N e p p c S t α µ α ρ α ρ α + Γ Γ + = + = =, 1 1, U -_ model

10 Interfacial Transfer Terms Mass Homogeneous condensation Heterogeneous evaporation Momentum Drag force Lift force Wall lubrication force Turbulent dispersion force Virtual mass SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

11 Subcooled Boiling Model '' Γ bl = πd 6 3 bw ρ q h g '' w fg f N '' subcooled saturated '' Γ lb = h T lb( sat T l ) h fg convection evaporation quenching convection evaporation quenching SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

12 Computational Grid Used for SVEA Fuel Assembly SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

13 Phase Distribution in Two-Phase Bubbly Flows Measured void fraction distribution in a 5x5 bundle: G = g/m 2 /s p = 31.9 bar, q = 543 W/m 2, inlet subcooling 6 SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

14 Phase Distribution in Two-Phase Bubbly Flows Void fraction Subchannel Number Measured Calculated Predicted void fraction distribution in a 5x5 bundle: G = g/m 2 /s p = 31.9 bar, q = 543 W/m 2, inlet subcooling 6 SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

15 Two-Phase Annular Flow Model Additional mass, momentum and energy conservation equations are solved for liquid film in annular flow Interfacial mass transfer includes Evaporation Entrainment Deposition Wall shear model based on local film thicness The modal enables prediction of dryout of the liquid film Worshop on Modelling and Measurements of Two-Phase Flows and Heat Transfer in Nuclear Fuel Assemblies, October , TH, Stocholm, Sweden 15

16 Annular Two-Phase Flows G = 450 g/m 2 /s, p = 70.8 bar, Inlet film mass flux, 10-2 g/ms Inlet film mass flux, 10-2 g/ms Outlet film mass flux, 10-2 g/ms Outlet film mass flux, 10 Outlet film thicness, 10 Liquid film thicness, 10-6 m -2 g/ms -6 m q = 1259 W/m 2, inlet subcooling thinnest film measured dryout Predicted thinnest liquid film is in neighborhood of rods which went under dryout SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

17 Annular Two-Phase Flows G = 1571 g/m 2 /s, p = 70.9 bar, q = 2612 W/m 2, inlet subcooling thinnest film measured dryout Predicted thinnest liquid film is on the rod which went under dryout SIAMUF-Seminarium, Forsningsöversit Flerfasströmning, Orenäs Slott, Glumslöv, otober

18 Conclusions Current model can be applied for prediction of phase distribution and heat transfer in dispersed two phase flows (bubbly and annular flows) Challenges for future development include: Prediction of turbulence structure in fuel assembly Phase distributions in two-phase non-disperse flows Prediction of CHF (DNB and dryout) based on mechanistic principles Worshop on Modelling and Measurements of Two-Phase Flows and Heat Transfer in Nuclear Fuel Assemblies, October , TH, Stocholm, Sweden 18

19 Conclusions (cont ed) Future focus will be on development of sub-models suitable for rod bundle geometry Validation should be performed against detailed measurements in rod bundles Validation against data obtained in pipes is not enough Worshop on Modelling and Measurements of Two-Phase Flows and Heat Transfer in Nuclear Fuel Assemblies, October , TH, Stocholm, Sweden 19