1. IMPACT CAPE-P: DNB Power Analysis Code for PWR FUEL Assembly - Evaluation Method - Analytical Step Calculation Method 3. Detection of DNB 1. Fuel Bundle 2. Each Subchannel 3-D Subchannel Analysis with Drift-flux Model Weismann Model, or Katto’s Model as Option 3-D Two-Phase Flow Analysis with Non-homogeneous and Non-equilibrium Two-fluid Model

2. IMPACT CAPE-P: Outline of 3-D Two-phase Flow Analysis Module  Analysis Coordinate: Cartesian Coordinate  Basic Equations - one pressure, non-homogeneous and non-equilibrium two-fluid model - mass, energy and three momentum conservation equations for vapor and liquid phases  Constitutive Equations - Lateral lift forces acting on bubbles: Suffman force, Wall effect force and Bubble dispersion force.  Model coefficients were given by empirical correlations. - Turbulence Model: Sato model  The eddy viscosity induced by bubbles was considered. - Interfacial drag force: Andersen model (C 0,V gj : Ishii model) - Interfacial heat transfer coefficient: Plesset and Zwick model for Saturated boiling and Unal model for Subcooled boiling

3. Fuel rod Core region Bubbly layer IMPACT CAPE-P: Outline of DNB Evaluation Module (Weisman Model)  A bubbly layer is formed by build-up of bubbles near the wall, under subcooled boiling condition.  DNB occurs when a void fraction of the bubbly layer exceeds the critical value.  In the calculation, nearest meshes from the wall are defined as a bubbly layer. Heated wall Bubbly layer Core region bubble

4. IMPACT CAPE-P: Verification of Two Phasae Flow Analysis Model (1) NUPEC Test - Void Distribution in Single Channel - Single channel void distribution tests under PWR conditions by NUPEC - Horizontal void distributions were measured. - Heated length : 1.825m, Measurements : 1.400m from the bottom Test Vessel (Titanium Alloy) Heater (Inconel) Measurement 0.5 1.0 0.0 Void Fraction Insulator (Alminum)

5. IMPACT CAPE-P: Verification of Two Phase Flow Analysis Model (2) Result of Void Distribution at High Pressure  Pressure: 14.7 MPa  Mass Flux: 5.0  10 6 kg/m 2 h  Power: 60 kW  Inlet Temperature: 573 K 3-D Analysis Result Measured Higher Void Fraction 0.4 0.5 0.6

6. IMPACT CAPE-P: Verification of Two Phase Flow Analysis Model (3) Result of Void Distribution at Low Pressure 3-D Analysis Result Measured  Pressure: 4.9 MPa  Mass Flux: 5.0  10 6 kg/m 2 h  Power: 80 kW  Inlet Temperature: 573 K 0.6 0.4 0.8 Lower Void Fraction

7. 9.5mm 12.6mm IMPACT CAPE-P: Validation by NUPEC Full Length 5  5 Test Analysis (1) NUPEC Test Apparatus and Analysis Region Heated Length: 3.658 m Grid Spacer with Mixing Vanes 12.6 mm 9.5 mm : High Power Rod (pf=1.0) : Low Power Rod (pf=0.85) Subchannel Analysis Region 3-D Two-phase Flow Analysis Region

8. Number of Grids: 12  12  135=19440 : with porous Mesh arrangement of XY section fuel rod 135 grids IMPACT CAPE-P: Validation by NUPEC Full Length 5  5 Test Analysis (2) Grid Model of Three-Dimensional Two-Phase Flow Analysis

9. IMPACT 7.0 Calculated DNB power (MW) Measured DNB power (MW) Average difference: -4.9%   =6.7% (Standard deviation) Pressure: 7.35-16.6 MPa Mass flux: 2-14  10 6 kg/m 2 h Inlet subcooling: 126-502 kJ/kg 6.0 5.0 4.0 3.0 2.0 1.0 0 2.03.0 4.05.06.07.0 Test Bundle: 5  5 Full scale CAPE-P: Validation by NUPEC Full Length 5  5 Test Analysis (3) Analysis Result

10. 1000 2000 3000 4000 5000 6000 7000 04812 16 Pressure (MPa) DNB Power (kW) IMPACT CAPE-P: Validation by NUPEC Full Length 5  5 Test Analysis (4) Pressure Effect on DNB Power : Measured : Calculated

11. 1000 2000 3000 4000 5000 6000 7000 02468101214 16 Mass Flux (  10 6 kg/m 2 h) DNB Power (kW) IMPACT CAPE-P: Validation by NUPEC Full Length 5  5 Test Analysis (5) Effect of Mass Flux on DNB Power : Measured : Calculated

12. 0 1000 2000 3000 4000 5000 6000 7000 100200 300400 500600 Inlet Subcooling (kJ/kg) DNB Power (kW) IMPACT CAPE-P: Validation by NUPEC Full Length 5  5 Test Analysis (6) Effect of Inlet Subcooling on DNB Power : Measured : Calculated