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


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


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


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


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


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


3. Case Study

Important Parameter

DNBR & Temperature - The preservation of fuel cladding

Flow - The relationship between status of

RCP & reactor core safety


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.



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.



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.


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.



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)



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


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.



• 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!!



• 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 )



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



• 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!!


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]


< 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.


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]


< 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]


Fig. 18. The relationship of core coolant temperature.

Fig. 19. The relationship of core fuel temperature.



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.



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.


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.


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.

loss of coolant flow accident

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