Loss of Coolant Flow Accident. < Group 6 Members > Kim Jun-o(99409-010) : Partial loss Accident Jun Ki-han(99409-038) : Complete loss Accident Lee Min-jae(99409-031) : Shaft seizure Accident Lee Keo-hyoung(99409-029) : Shaft break Accident. Contents. 1. Introduction. 2. Summary.
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< Group 6 Members >
Kim Jun-o(99409-010) : Partial loss Accident
Jun Ki-han(99409-038) : Complete loss Accident
Lee Min-jae(99409-031) : Shaft seizure Accident
Lee Keo-hyoung(99409-029) : Shaft break Accident
3. Case Study
- A RCP failure by electronic trouble.
- All RCPs failure by total loss of power
- Impeller seizure by friction
- Shaft break
Motor Shaft &Pump Shaft
Fig. 1. The illustration of Westinghouse Reactor Coolant Pump, From Westinghouse Electric Corporation
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
Fig. 2. Thermal design heat flux parameters in a burnout-limited core.
RCP’s capability loss
→ Flow decrease
→ Low flow trip signal
→ Reactor trip
→ DNBR change
Fig. 3. An illustration of RCP and reactor vessel
- The preservation of fuel cladding
- The relationship between status of RCP & reactor core safety
Fig. 4. Flow change of each state.
Fig. 5. Fuel temperature change.
Fig. 6. Core coolant temperature comparison.
Fig. 7. DNBR change.
Fig. 8. Time-Flow graph.
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.
< 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.
Reactor trip function occur (8s)
Fig. 9. (a) Time-Power distribution graph, (b) Time-DNBR graph
< 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
- Time scale : 0.4 sec
- Rotor seizure in RCP 1 after 5.2 sec
- Compare with normal condition
- 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.
Fig. 11. Flow.
(ºC)3-3. RCP Shaft Seizure (3)
Fig. 12. Fuel temp : average.
Fig. 13. Fuel temp : Zone 7
Fig. 14. DNBR
Fig. 14. Pressurizer pressure
Fig. 15. DNBR
So, it’s safe!!
< 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.
Fig. 16. The relationship of RCP #1 flow.
< 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. 17. The relationship of RCP #2 flow.
< Core Coolant Temperature >
Shaft seizure accident’s core coolant temperature is higher than the shaft break accident’s temperature.
Fig. 18. The relationship of core coolant 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.
Fig. 19. The relationship of core fuel temperature.
Fig. 20. The relationship of DNBR and Zone.
Fig. 21. The relationship of DNBR and core temperature.
< 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. 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.