Lungmen Startup Test Prediction BenchmarkPCTRAN/ABWR vs. GE

ForTaiwan Power Company

ByMicro-Simulation Technology

December 2008

In cooperation with National Tsinghua University, MST has run PCTRAN/ABWR to benchmark GE’s predictions in most of the above cases. Reasonable agreement is achieved in all cases. In order to run the startup tests, a number of new features were added into the updated version of PCTRAN/ABWR model:

1. Turbine Header Pressure Control

Operator can manually reset the header pressure during normal operation or post trip by clicking the “A/M” button and type in the new set point.

2. Hot Shutdown Cooldown Control

After a reactor trip and when the condition is stabilized, a rapid cooldown at 100ºF/hr can be activated by clicking the “A/M” button in the recirculation control panel.

3. Reactor Internal Pumps Runback Control

A “Runback” speed control is provided for all RIP’s speed demand to designed or operator-designated RPM.

4. SCRRI

Selected Control Rod Run-in button is provided. This function has a selected control rod group run-in to prevent a reactor trip after turbine trip. The reactivity and run-in time is adjustable in the input database.

5. The flux/flow operation map of Lungmen is incorporated into the “View” menu button.

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The new PCTRAN/ABWR operation mimic is shown below:

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The report “Startup Test Prediction” WST-GE-0006024” by GE has provided the following test matrix:

TPC is encouraged to install PCTRAN/ABWR and run all these and any other cases to get familiar with the plant’s transients during startup. The experience and feedback will be valuable in preparation of the startup.

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Case 1 Loss of Feedwater Heating at TS4 (80% power, 100% flow)

TS4 is prepared as IC8 with power factor PF = 0.8 and ANS = 0.8. Since at full power the feedwater is heated from 18ºC ambient temperature to 215ºC for a range about 200ºC, a partial loss of heaters by 37ºC corresponds to 37/200 = 18.5%. Malfunction 14 is initiated for a factor of 18.5% with ramp time of 40 seconds for this case. At end of 40 seconds, the RIP demand is runback to 90% using the “Runback” button and SCRRI is initiated. The original total rod insertion is 98% in PCTRAN/ABWR. By pressing the SCRRI button, the selected control rods insertion corresponds to about 6% insertion or to the overall position of 92%. The insertion time is about 145 seconds. PCTRAN/ABWR transient results are shown side-by-side with the GE analysis.

Comparing to Fig 5.1-1 of the GE Startup Test Prediction report, the feedwater initial enthalpy of 900 KJ/kg corresponds to PCTRAN’s feedwater temperature of 215ºC. It is ramped down by 37ºC to 178ºC in 40 seconds. The core inlet sub-cooling margin increases the same way as Fig. 5.1-2.

The core inlet flow, neutron flux and average heat flux are almost identical with Fig. 5.1-2. The reactor is stabilized at about 36% power in 250 seconds. The reactor dome and turbine header pressure from PCTRAN has the header pressure controller functioning. As a result it does not show the deep drop by about 250 Kpa in GE’s Fig. 5.1-3. The feedwater and steam flows drop from 80% to under 40% the same as Fig. 5.1-4. The water level rise in PCTRAN (about 5 cm) also has the feedwater controller in effect so that it is not as significant as in Fig. 5.1-4 (by about 20 cm). The reactivity response is consistent with Fig. 5.1-5. We do not understand GE’s “% NBR” unit system. Zero % corresponds to nuclear boiling rated is all right; but what is 100% for reactivity? Is it shutdown reactivity? or % in dk/k? Their clarification is needed. Our unit is in dollar.

The following tables and figures are extracted from Taiwan Power Company Lungmen Project Startup Test Prediction report by GE Nuclear Energy, SWT-GE-006024, 3/1/2005. In comparison with the above PCTRAN figures they are in good agreement.

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In PCTRAN’s ABWR model there is turbine header pressure control. When the pressure error becomes larger than the dead-band, it regulates the steam flow to keep the pressure dropping as the GE figure.

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Case 2 Loss of Feedwater Heating at TS5 (90% power, 100% flow)

TS5 is prepared as IC9 with power factor PF = 0.9 and ANS = 0.9. Since at full power the feedwater is heated from 18ºC ambient temperature to 215ºC for a range about 200ºC, a partial loss of heaters by 37ºC corresponds to 37/200 = 18.5%. Malfunction 14 is initiated for a factor of 18.5% with ramp time of 40 seconds for this case. At end of 40 seconds, the RIP demand is runback to 90% using the “Runback” button and SCRRI is initiated. The original total rod insertion is 98% in PCTRAN/ABWR. By pressing the SCRRI button, the selected control rods insertion corresponds to about 6% insertion or to the overall position of 92%. The insertion time is about 145 seconds. PCTRAN/ABWR transient results are shown side-by-side with the GE analysis.

Comparing to Fig 5.1-1 of the GE Startup Test Prediction report, the feedwater initial enthalpy of 900 KJ/kg corresponds to PCTRAN’s feedwater temperature of 215ºC. It is ramped down by 37ºC to 178ºC in 40 seconds. The core inlet sub-cooling margin increases the same way as Fig. 5.1-6.

The core inlet flow, neutron flux and average heat flux for PCTRAN are compared against Fig. 5.1-6. The reactor is stabilized at about 45% power vs. GE’s 50% in 250 seconds. The reactor dome pressure from PCTRAN has dropped more than GE’s. The water level rise and reactivity response are consistent with Fig. 5.1-8 and 9.

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Case 3 One RIPT Test at TS 6

One Reactor Internal Pump is tripped at TS 6 (100% power and 100% flow). The power is stabilized around 97%. The reactor pressure, water level and reactivity feedback are all in good agreement with the GE report.

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Case 4 One RIPT Test at TS 3

One Reactor Internal Pump is tripped at TS 3 (75% power and 100% flow)

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Case 5 One RIPT then Restart at TS 6

One Reactor Internal Pump is tripped at TS 6 (100% power and 100% flow) condition; then it is restarted in 5 seconds.

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Case 6 Turbine Trip at 50% Power/ 50% Flow (TS 2)

We start PCTRAN by selecting IC12 for 50% power / 50% flow and MF 9 for turbine trip. Then press the “Runback” button and set the RPM demand at 45% and start SCRRI all simultaneously.

The reactor power is stabilized around 38%. The results are quite comparable to GE’s predictions.

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Case 7 Feedwater Pump Trip at TS6 (100% Power)

Trip of one turbine-driven feedwater pump drops the total feedwater flow to 55%. Startup of the motor-driven feedwater pump adds 20% to a total of 75%. Runback of all RIP’s to 40% at maximum rate increases the voids and reduces the core power. PCTRAN/ABWR simulation is closely comparable to GE prediction.

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As explained earlier there is greater difference in vessel pressure rise between PCTRAN and GE analyses because the pressure regulator is in effect.

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Exception: If RIP runback was to 50% instead, the level dropped too much in PCTRAN that should have reached L3 low-level scram (40 cm below normal).

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Case 8 Reactor Internal Pump Trip

Three RIP’s are tripped from TS6 100% power condition. The test was conducted by setting the full power ICThermoData RCLP = 3 to bundle 3 of the RIP’s in the mimic left side. Otherwise the default number is 4 since normally 4 pumps trip on L3 low-level. The sequence and GE report transient figures are shown below:

As a result of 3 RIP trip, the core inlet flow decreases to 70%. The voids increase and level swells. Both are observed in GE and PCTRAN transient figures. It is still within L3 and L8 bounds and scram does not occur. The reactivity changes and power is reduced to about 85%. The feedwater and steam flows also decrease to about 85% - consistent with the reduced power level. All are in good agreement.

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Loss of Offsite Power and Turbine Trip

Case 9 TS1 loss offsite power at 20% power and 38% flow

IC10 is prepared for Test TS1

PCTRAN run starts with turbine trip and FW pump trip and shortly later (3 seconds) RIP trip. Subsequently bypass loss and scram on L3 is the same as GE report. Trend of the reactor water level and reactivity transients are similar. However, the core inlet subcooling margin goes down instead of up. Also the vessel pressure rise trend should lift the SRV’s rather than keep going up. Because of FW pump trip, the water level should stay low rather than recover.

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Case 10 Turbine Trip at 100% Power TS6

IC1 is 100% power with 100% flow. The sequence of events is:

We start PCTRAN by selecting MF 9 for turbine trip and pressing the “Runback” button and setting the RPM demand at 45%. SCRRI is started simultaneously. The results are quite comparable to GE’s figures.

The core subcooling of PCTRAN after turbine trip has used the same feedwater temperature as power operation. If unheated is used it should go up the same as GE’s prediction.

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PCTRAN’s vessel pressure rise is positive in contrast to GE’s negative (decrease) trend. PCTRAN’s bypass flow is less than GE’s. This is due to the fast-opening logic is not rapid enough. As a result the vessel pressure rises after turbine trip and further has lifted a few safety relief valves.

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The feedwater and vessel steam flows stabilize around 50%. They are consistent with the GE’s prediction.

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The water level stabilizes to original level (386 cm TAF). Its trend is the same as GE’s.

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The reactivity responses of the two analyses are very comparable.

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Load Rejection is different from a turbine trip only by the initiating event is closing the turbine control valve for the former and the stop valve for the later. There is a difference in split second between the valves’ closing time. The subsequent events of SCRRI and RIP runback are the same. As a result, hardly any significant difference is observed in ODYN’s predictions. PCTRAN uses half a second as the time step in its simulation. Therefore essentially the same are expected for these two. No separate analysis is necessary.

Case 11 Reactor Full Isolation

All MSIV’s are closed for this event. The reactor is tripped on isolation signal. Then four RIP’s are tripped on high dome pressure. Following are the transient plots. The two analyses are in good agreement.

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Case 12 Fast Load Reduction

ABWR has a fast load reduction function from 100% to zero within 35 seconds without a reactor trip. It is typically conducted to about 5% house load then trip the turbine. The vessel water level should be between L3 and L8 without triggering a scram.

IC1 of 100% power is initiated with selection of MF15 for turbine control valve closing to zero (100% malfunction factor) in 35 seconds ramp time. Simultaneously SCRRI is initiated and all RIP’s are runback to 45% (by clicking the “runback speed” button. The results are very comparable to GE’s prediction. One exception is the “vessel pressure rise” transient – for this event as well as every other one: our prediction is the vessel pressure increases (positive) rather than GE’s decrease (negative). The turbine control valve is closing so that the header pressure must go up; that opens up the bypass valves to relieve the vessel steam. We do not understand the reason for GE’s prediction unless their definition is somewhat different.

Everything else is quite comparable. The feedwater and bypass steam flows, and core flow drop to about 50 – 60 % without a scram. The water level oscillates a few times and stabilizes to the original level. The rod reactivity is exactly as programmed and its feedback in void and Doppler are almost identical between the two studies.

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