Download - Loss of Coolant Flow Accident
Loss of Coolant Flow Accident
< Group 6 Members >Kim Jun-o(99409-010) : Partial loss AccidentJun Ki-han(99409-038) : Complete loss AccidentLee Min-jae(99409-031) : Shaft seizure AccidentLee Keo-hyoung(99409-029) : Shaft break Accident
Loss of Coolant Flow Accident by Group 6
Contents
1. Introduction
2. Summary
3. Case Study
4. Conclusion
Loss of Coolant Flow Accident by Group 6
1. Introduction
Loss of Coolant Flow Accident
One or more RCPs do not work.
Core coolant flow is decreasing.
External reason : Voltage is cut off
Internal reason : Shaft seizure or Break
Loss of Coolant Flow Accident by Group 6
2. Summary (1)
Comparison of Accident Type
Partial loss of coolant flow (Condition Ⅱ) - A RCP failure by electronic trouble. Complete loss of coolant flow (Condition Ⅲ) - All RCPs failure by total loss of power RCP shaft seizure (Condition Ⅳ) - Impeller seizure by friction 3-4 RCP shaft break (Condition Ⅳ) - Shaft break
Loss of Coolant Flow Accident by Group 6
2. Summary (2)
Reactor Coolant Pump (RCP)
Flywheel
Motor
Motor Shaft &Pump Shaft
Impeller &Diffuser
Fig. 1. The illustration of Westinghouse Reactor Coolant Pump, From Westinghouse Electric Corporation
Loss of Coolant Flow Accident by Group 6
2. Summary (3)
DNBR
Fig. 2. Thermal design heat flux parameters in a burnout-limited core.
DNB heat flux _Reactor local heat flux
< Minimum DNBR >
Occurs near the two-thirds of the core height
The closest approach of critical heat flux curve to the hottest channel curve as the pressure change in the core
Loss of Coolant Flow Accident by Group 6
2. Summary (4)
Common Phenomenon
RCP’s capability loss→ Flow decrease→ Low flow trip signal→ Reactor trip→ DNBR change
Fig. 3. An illustration of RCP and reactor vessel
Loss of Coolant Flow Accident by Group 6
3. Case Study
Important Parameter
DNBR & Temperature - The preservation of fuel cladding
Flow - The relationship between status of
RCP & reactor core safety
Loss of Coolant Flow Accident by Group 6
3-1. Partial Loss of Flow (1)
0 10 20 30 40 50 60 70 80
-1000
0
1000
2000
3000
4000
5000
Average (failure)
RCP 1 (failure)
RCP 2&3 (working)
Steady State
Flow (Kg/sec)
Time (sec)
• Test condition : RCP 1 failure (at 5.2 sec)• Flow increase on the other 2 RCPs• Reverse flow after RCP failure.
Fig. 4. Flow change of each state.
Loss of Coolant Flow Accident by Group 6
3-1. Partial Loss of Flow (2)
0 10 20 30 40 50 60 70 80290
291
292
293
294
295
Accident State
Steady State
Time (sec)
Core Coolant Temperature (C)
0 20 40 60 80
300
400
500
600
700
800
Time (sec)
Average Fuel Temperature(C)
0 20 40 60 80
300
400
500
600
700
800
Time (sec)
Average Fuel Temperature(C)• Reactor & turbine trip on low flow signal (at 8.0 sec)
• Core coolant temperature decrease as thermal power decrease
Fig. 5. Fuel temperature change.
Fig. 6. Core coolant temperature comparison.
Loss of Coolant Flow Accident by Group 6
3-1. Partial Loss of Flow (3)
0 1 2 3 4 5 6 7 8 9 102.30
2.35
2.40
2.45
2.50
Time (sec)
DNBR
• DNBR does not decrease during this accident
Fig. 7. DNBR change.
Loss of Coolant Flow Accident by Group 6
3-2. Complete Loss of Flow (1)
0 5 10 15 20
40
50
60
70
80
90
100
Flo
w (
kg/s
ec)
Time (sec)
flow rate
Malfunction injection (5.2s)
90% flow rate
Reactor trip function occur (8s)
90% flow rate spot (7.4s)
After malfunction injection, flow is decreasing fast.
Reactor trip function occur when the flow reaches at 90% of nominal flow.
CNS result shows the reactor trip function work properly.
Fig. 8. Time-Flow graph.
Loss of Coolant Flow Accident by Group 6
3-2. Complete Loss of Flow (2)
0 2 4 6 8 10 12 14 160.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Po
we
r d
istr
ibu
tion
Time (s)
power distribution
0 2 4 6 8 10 12 14 160
2
4
6
8
10
DN
BR
Time (s)
DNBR
Malfunction injection(5.2s)
Reactor trip function occur (8s)
< DNBR and Power distribution >
DNBR does not decrease below 1.3.
After 6 second, DNBR is maintained at 10.
DNBR and power distribution are inverse-proportion.
Fig. 9. (a) Time-Power distribution graph, (b) Time-DNBR graph
(a)
(b)
Loss of Coolant Flow Accident by Group 6
3-2. Complete Loss of Flow (3)
0 5 10 15 20 25 30 35 40
300
400
500
600
700
800C
ore
tem
pe
ratu
re
Time (s)
core temperature
0 5 10 15 20 25 30 35 40
1000
1500
2000
2500
3000
3500
4000
4500
5000
Coo
lant
Flo
w
Time (s)
Coolant Flow
0 5 10 15 20 25 30 35 40
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Pow
er d
istr
ibut
ion
Time (s)
Power distribution
< Temperature Tendency >
Temperature is related with heat generation and heat coefficient.
Heat generation is proportional of power distribution.
Heat coefficient can be obtained by mass flow .
Fig. 10. (a) Time-Core temperature graph, (b) Time-Power distribution graph, (c) Time-Coolant flow graph
(a)
(b)
(c)
Dittus-Boelter correlation
Loss of Coolant Flow Accident by Group 6
3-3. RCP Shaft Seizure (1)
In CNS (Compact Nuclear Simulator)
Test Condition- Time scale : 0.4 sec- Rotor seizure in RCP 1 after 5.2 sec- Compare with normal condition
Result - Flow reduced rapidly after rotor seizure- Reactor trip on low flow signal- Control rods begin to drop immediately- After drop of control rods, fuel temperature decreased- Maximum pressurizer pressure is under 2385 psia- DNB does not occur in the accident of rotor seizure- So, it’s safe.
Loss of Coolant Flow Accident by Group 6
3-3. RCP Shaft Seizure (2)
• Reactor trip on low flow signal ( 90% of normal flow )• Reverse flow occur after seizure
Fig. 11. Flow.
0 2 4 6 8 10 12 14 16 18
-2000
-1000
0
1000
2000
3000
4000
5000
Flow : RCP 1
Flo
w (
kg/s
ec)
Time (Sec)
Reactor trip!!
Loss of Coolant Flow Accident by Group 6
3-3. RCP Shaft Seizure (3)
• Fuel temperature decreased after control rods drop
Fig. 12. Fuel temp : average.
Fig. 13. Fuel temp : Zone 7
0 5 10 15 20 25 30 35
300
400
500
600
700
800
Te
mp
()
℃
Time (sec)
Fuel temp : averageControl rod begins to drop
Control rod completely droped(º C )
0 2 4 6 8 10 12 14 16 18300
400
500
600
700
800
900
1000
1100
Tem
p (
)℃
Fuel temp : Zone 7
Time (sec)
( º C )
Loss of Coolant Flow Accident by Group 6
3-3. RCP Shaft Seizure (4)
Fig. 14. DNBR
0 10 20 30 40 50 60 70
1950
2000
2050
2100
2150
2200
2250
2300
2350
2400
2450
2500
Time (Sec)
Pre
ssur
e (p
sig)
2385
Pressurizer pressure
• Maximum pressurizer pressure at 8.4 sec• But the pressure is under 2385 psig
Fig. 14. Pressurizer pressure
Loss of Coolant Flow Accident by Group 6
3-3. RCP Shaft Seizure (5)
• DNB dose not occur in CNS
Fig. 15. DNBR
0 2 4 6 8 10 12 14 16 180
2
4
6
8
10
12
Time (Sec)
DNBRD
NB
R
1.6
So, it’s safe!!
Loss of Coolant Flow Accident by Group 6
3-4. RCP Shaft Break (1)
0 5 10 15 20 25 30
-2000
-1000
0
1000
2000
3000
4000
5000
Reverse Flow Points
RC
P #
1 F
low
[kg/
sec]
Time [sec]
RCP Shaft Seizure Accident RCP Shaft Break Accident
< Flow of RCP #1 in 5.6 ~ 10.8 sec >
Shaft seizure accident : Reverse flowShaft break accident : Flow decreased
< Flow of RCP #1 after 10.8 sec >Shaft break accident : Reverse flowThis flow is lower than shaft seizure’s.
0 10 20 30 40 50 604600
4650
4700
4750
4800
4850
Reverse Flow Pointsof RCP #1
RC
P #
2 F
low
[kg/
sec]
Time [sec]
RCP Shaft Seizure Accident RCP Shaft Break Accident
< Flow of RCP #2 in 5.6 ~ 10.8 sec >
Shaft seizure accident’s flow is higherthan shaft break accident’s flow.
< Flow of RCP #2 after 10.8 sec >
Shaft seizure accident’s flow is lowerthan shaft break accident’s flow.
Fig. 16. The relationship of RCP #1 flow.
Fig. 17. The relationship of RCP #2 flow.
Loss of Coolant Flow Accident by Group 6
3-4. RCP Shaft Break(2)
0 10 20 30 40 50 60288
289
290
291
292
293
294
295
296
Cor
e C
oola
nt T
empe
ratu
re [?
]
Time [sec]
RCP Shaft Seizure Accident RCP Shaft Break Accident
< Core Coolant Temperature >
Shaft seizure accident’s core coolant temperature is higher than the shaft break accident’s temperature.
< Core Fuel Temperature (Zone 25) >
Shaft seizure accident’s core coolant temperature is the same as shaft break accident’s temperature.
Like shaft break accident, shaft seizure accident is also safe.
0 10 20 30 40 50 60
300
350
400
450
500
550
Cor
e F
uel T
empe
ratu
re(Z
one
25)
[?]
Time [sec]
RCP Shaft Seizure Accident RCP Shaft Break Accident
Fig. 18. The relationship of core coolant temperature.
Fig. 19. The relationship of core fuel temperature.
Loss of Coolant Flow Accident by Group 6
3-4. RCP Shaft Break(3)
Fig. 21. The relationship of DNBR and core temperature.
0 10 20 30 40 50 60 7025
20
15
10
5
Zon
e [#
]
Time [sec]
Maximum Core Temperature Zone Minimum DNBR Zone
< 0 ~ 10 sec >
Fuel and coolant show much difference in temperature
< After 10 sec >
After control rod drop, the difference becomes smaller.
=> Minimum DNBR zone is under maximum core temperature zone.
1 2 3 4 5 6 725
20
15
10
5
Zon
e [#
]
DNBR
Fig. 20. The relationship of DNBR and Zone.
Loss of Coolant Flow Accident by Group 6
3-4. RCP Shaft Break(4)
RCP Flow and Fuel Temperature
RCP #2, 3 flow under the influence of RCP #1 flow.
RCP flow has influence on reactor safety.
Minimum DNBR zone and maximum core temperature zone is not same.
Loss of Coolant Flow Accident by Group 6
4. Conclusion
Results of CNS Analysis
RCP flow has great influence on reactor safety.
DNB does not occur in any case of loss of flow accident in CNS.
Results of CNS have many similarities with FSAR, even safer.
Analysis of the simulation shows that LOFA is safe in Kori 3, 4.
Loss of Coolant Flow Accident by Group 6
Reference
1. E.E.Lewis, “Nuclear Power Reactor Safety”, John Wiley & Sons Inc, Canada, 1977
2. M.M.El-Wakil, “Nuclear Heat Transport”, American Nuclear Society, USA, 1978
3. Y.A.Cengel, “Heat Transfer : A Practical Approach”, McGraw-Hill Book Co., Singapore, 1999
4. Kori 3,4 FSAR.