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Loss of Coolant Flow Accident

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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Loss of Coolant Flow Accident

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  1. 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

  2. Contents 1. Introduction 2. Summary 3. Case Study 4. Conclusion

  3. 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

  4. 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

  5. 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

  6. 2. Summary (3) • DNBR 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.

  7. 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

  8. 3. Case Study • Important Parameter • DNBR & Temperature - The preservation of fuel cladding • Flow - The relationship between status of RCP & reactor core safety

  9. 3-1. Partial Loss of Flow (1) Fig. 4. Flow change of each state. • Test condition : RCP 1 failure (at 5.2 sec) • Flow increase on the other 2 RCPs • Reverse flow after RCP failure.

  10. 3-1. Partial Loss of Flow (2) • Reactor & turbine trip • on low flow signal • (at 8.0 sec) Fig. 5. Fuel temperature change. • Core coolant temperature • decrease as thermal power • decrease Fig. 6. Core coolant temperature comparison.

  11. 3-1. Partial Loss of Flow (3) Fig. 7. DNBR change. • DNBR does not decrease during this accident

  12. 3-2. Complete Loss of Flow (1) 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.

  13. 3-2. CompleteLoss of Flow (2) < 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. (a) Reactor trip function occur (8s) Malfunction injection(5.2s) (b) Fig. 9. (a) Time-Power distribution graph, (b) Time-DNBR graph

  14. 3-2. Complete Loss of Flow (3) < 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 . (a) Dittus-Boelter correlation (b) Fig. 10. (a) Time-Core temperature graph, (b) Time-Power distribution graph, (c) Time-Coolant flow graph (c)

  15. 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.

  16. 3-3. RCP Shaft Seizure (2) Fig. 11. Flow. • Reactor trip on low flow signal ( 90% of normal flow ) • Reverse flow occur after seizure

  17. (ºC) (ºC) 3-3. RCP Shaft Seizure (3) Fig. 12. Fuel temp : average. Fig. 13. Fuel temp : Zone 7 • Fuel temperature decreased after control rods drop

  18. 3-3. RCP Shaft Seizure (4) Fig. 14. DNBR Fig. 14. Pressurizer pressure • Maximum pressurizer pressure at 8.4 sec • But the pressure is under 2385 psig

  19. 3-3. RCP Shaft Seizure (5) Fig. 15. DNBR • DNB dose not occur in CNS So, it’s safe!!

  20. 3-4. RCP Shaft Break (1) < 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.

  21. 3-4. RCP Shaft Break(2) < 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.

  22. 3-4. RCP Shaft Break(3) 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.

  23. 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.

  24. 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.

  25. 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.

  26. Thank You !

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