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

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 (C0,Vgj: Ishii model) - Interfacial heat transfer coefficient: Plesset and Zwick model for Saturated boiling and Unal model for Subcooled boiling

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

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)

IMPACT

CAPE-P: Verification of Two Phase Flow Analysis Model(2) Result of Void Distribution at High Pressure

Pressure: 14.7 MPa

Mass Flux: 5.0106 kg/m2h

Power: 60 kW

Inlet Temperature: 573 K3-D Analysis Result

Measured

Higher Void Fraction

0.4

0.5

0.6

IMPACT

CAPE-P: Verification of Two Phase Flow Analysis Model(3) Result of Void Distribution at Low Pressure

3-D Analysis ResultMeasured

Pressure: 4.9 MPa

Mass Flux: 5.0106 kg/m2h

Power: 80 kW

Inlet Temperature: 573 K

0.6

0.4

0.8

Lower Void Fraction

heated l ength3. 658m

gri d spacer wi thmi xi ng vanes

9.5mm12.6mm

IMPACT

CAPE-P: Validation by NUPEC Full Length 55 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

Number of Grids:

1212135=19440

: with porous

Mesh arrangement of XY section

fuel rod

135 grids

IMPACT

CAPE-P: Validation by NUPEC Full Length 55 Test Analysis

(2) Grid Model of Three-Dimensional Two-Phase Flow Analysis

IMPACT

7.0C

alc

ula

ted

DN

B p

ow

er

(MW

)

Measured DNB power (MW)

Average difference: -4.9%

=6.7% (Standard deviation)

Pressure: 7.35-16.6 MPa Mass flux: 2-14 106 kg/m2hInlet subcooling: 126-502 kJ/kg

6.0

5.0

4.0

3.0

2.0

1.0

0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Test Bundle:

55 Full scale

CAPE-P: Validation by NUPEC Full Length 55 Test Analysis

(3) Analysis Result

1000

2000

3000

4000

5000

6000

7000

0 4 8 12 16

Pressure (MPa)

DN

B P

ow

er

(kW

)

IMPACT

CAPE-P: Validation by NUPEC Full Length 55 Test Analysis

(4) Pressure Effect on DNB Power

: Measured

: Calculated

1000

2000

3000

4000

5000

6000

7000

0 2 4 6 8 10 12 14 16

Mass Flux (106 kg/m2h)

DN

B P

ow

er

(kW

)

IMPACT

CAPE-P: Validation by NUPEC Full Length 55 Test Analysis

(5) Effect of Mass Flux on DNB Power

: Measured

: Calculated

0

1000

2000

3000

4000

5000

6000

7000

100 200 300 400 500 600

Inlet Subcooling (kJ/kg)

DN

B P

ow

er

(kW

)

IMPACT

CAPE-P: Validation by NUPEC Full Length 55 Test Analysis

(6) Effect of Inlet Subcooling on DNB Power

: Measured

: Calculated