Comparison of MARS Code Analysis on DVI Line Break LOCA at Different

Break Sizes between SNUF and APR1400

2009/05/21

Korean Nuclear Society Spring Meeting

Xin-Guo Yu, Keo-Hyoung Lee, Goon-Cherl ParkNuclear Thermo-hydraulics Engineering Lab.

Seoul National Univ.

11

Outline

22

Introduction

Background

33

Hot- LegCold- Leg

Broken DVI- Line

Upper Downcomer

Core Pressure

Fig. 1. Flow Path of Coolant in DVI Line Break LOCA

Introduction

Description of SNUF RHRP(Reduced Height and Reduced

Pressure) facility

Scaled-down from APR1400

Designed to simulate LOCA of APR1400

Scaling Factors of GeometryLength: 1/6.4

Area: 1/178

Operation CapabilityMaximum Pressure: 8 bar

Maximum Power: 150 kW

44

Fig. 2. Schematic of SNUF (Seoul National Univ. Facility)

Introduction

Objectives and Analysis Strategy of Research:

55

Energy Scaling Method and Test Conditions

Derivation of Energy Scaling MethodMass and energy conservation equations in primary system

Non-dimensionalize and energy conservation equation with respect to initial values of primary system

⇒ Mass inventory :

⇒ Enthalpy difference between cold leg and hot leg :

⇒ Thermal power :

66

in out

dMm m

dt & &

c in in out out

dMhQ m h m h

dt & & 1hdV

h hdVMdV

M dVWhere

Where

: mass inventory in primary system

0M

0h

cQ

Energy Scaling Method and Test Conditions

Set , to conserve time scale, the scaling criteria are given as follows:

77

*

*0 0

in outm mdM

dt M M

& &

* *

*0 0 0 0 0 0

c in in out outQ m h m hdM h

dt M h M h M h

& &

1

0

1in

R

m

M

&

0

1out

R

m

M

&

0 0

1c

R

Q

M h

0

1in

R

h

h

0

1out

R

h

h

⇒ Energy scaling criteria

※ Henry-Fauske critical flow model adopted to obtain estimated critical mass flow rate

⇒ Ratio of broken area : 0RR

cR

MA

G

Dimensionless conservation equations

cRG

Energy Scaling Method and Test Conditions

Steady-state and Transient Conditions Conservative core power

Normal operation: 102 % of normal power Decay Heat: 120 % of decay heat (ANS73 model)

Test conditions obtained from energy scaling method

Table 1. Steady State Conditions of APR1400 and SNUF Table 2. Transient Conditions of SNUF

88

Parameter APR1400 SNUFScalingFactor

Core Power 4,063 MW 108 kW 2.66E-05

Primary System Pressure

157 bar 6.3 bar 0.04

Secondary System Pressure

69 bar 1.725 bar 0.025

Hot-leg Temperature 324.53 oC 145.51 oC 0.448

Cold-leg Temperature 290.85 oC 126.91 oC 0.436

Mass flow rate in the core

10,496 kg/s 0.673 kg/s 6.41E-05

Mass flow rate in secondary system

4,400 kg/s 3.53 kg/s 8.02E-04

Parameter 100 % 50 % 25 %

Core Power 0 ~ 100 s 100 ~ 300 s 300 ~ 1000 s

71.4 kW47.6 kW37.4 kW

72.7 kW47.6 kW37.5 kW

73.1 kW47.8 kW37.6 kW

Break Size 158 mm2 78 mm2 39 mm2

HPSI flow rate 45.9 g/s 40.3 g/s 31.8 g/s

SIT flow rate 28.0 g/s 20.4 g/s N/A

SIT temperature 20.27 oC 20.27 oC 20.27 oC

Simulation Results and Discussion

Primary System Pressures at Different DVI Line Break Accident

99

0 100 200 300 400 5000.0

0.2

0.4

0.6

0.8

1.0

SNUF APR1400

Pri

mar

y S

yste

m P

ress

ure

[P

/P0]

Time [s]

0 100 200 300 400 500 6000.0

0.2

0.4

0.6

0.8

1.0

SNUF APR1400

Pri

mar

y S

yste

m P

ress

ure

[P

/P0 ]

Time [s]

0 200 400 600 800 10000.0

0.2

0.4

0.6

0.8

1.0

SNUF APR1400

Pri

mar

y S

yste

m P

ress

ure

[P

/P0 ]

Time [s]

Fig. 3. Primary System Pressureat 100% Break Accident

Fig. 4. Primary System Pressure at 50% Break Accident

Fig. 5. Primary System Pressureat 25% Break Accident

• Good agreement of change rate of primary system pressure between SNUF and APR1400 in each case of accidents

• Test conditions are reasonable, in the view points of energy and pressure in the primary system during accident

Simulation Results and Discussion

1010

• Timing of downcomer seal clearing phenomenon did not show good agreements between SNUF and APR1400 for 50% and 25% break accident.

• It is due to no consideration of momentum conservation in the process to determine test conditions with energy scaling method.

0 200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Do

wn

com

er

Co

llap

sed

Wa

ter

Le

vel [

H/H

o]

Time [s]

SNUF APR1400

0 100 200 300 400 500 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Do

wn

com

er

Co

llap

sed

Wa

ter

Le

vel [

H/H

o]

Time [s]

SNUF APR1400

Downcomer Water Level at Different DVI Line Break Accident

Fig. 6. Downcomer Water Level at 100% Break Accident

Fig. 7. Downcomer Water Level at 50% Break Accident

Fig. 8. Downcomer Water Level at 25% Break Accident

0 100 200 300 400 5000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Do

wn

com

er

Co

llap

sed

Wa

ter

Le

vel [

H/H

o]

Time [s]

(100) ()

Simulation Results and Discussion

Core Water Level at Different DVI Line Break Accident

1111

0 100 200 300 400 5000.0

0.2

0.4

0.6

0.8

1.0

SNUF APR1400

Co

re C

oll

apse

d W

ater

Lev

el [

H/H

0]

Time [s]

0 100 200 300 400 500 6000.0

0.2

0.4

0.6

0.8

1.0

SNUF APR1400

Co

re C

oll

apse

d W

ater

Lev

el [

H/H

0]

Time [s]

0 200 400 600 800 10000.0

0.2

0.4

0.6

0.8

1.0

SNUF APR1400

Co

re C

oll

apse

d W

ater

Lev

el [

H/H

0]

Time [s]

Fig. 10. Core Water Level at 75% Break Accident

Fig. 11. Core Water Level at 25% Break Accident

Fig. 9. Core Water Level at 100% Break Accident

• Simulation results of APR1400 shows lower core water level compared to that of SNUF after break, 75s / 130s / 250s for 100%, 50% and 25% break accidents respectively

• Large discrepancy of core water level between SNUF and APR1400 due to difference of timing of downcomer seal clearing phenomenon and no consideration of momentum conservation

Conclusion

Summary• Reasonable test conditions was obtained from energy scaling method

∵ good agreement with primary system pressure between SNUF and APR1400

• Water levels of downcomer and core were not scaled down resonalbly

∵ no consideration of momentum conservation in deriving scaling method

• Additional study is required to scale-down the momentum in the loop

Further Study• Study dimensionless momentum equation to obtain dimensionless criteria

to determine test conditions for SNUF experiment

• Conduct SNUF experiment to research DVI line break LOCA, served as a counterpart of ATLAS test conducted in KAERI

• Validate capability of MARS code in simulating DVI-line break LOCA

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