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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
1212
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