Feedwater Flashcards
Explain how the SG is being fed during plant startup.
Aux Feed November- 2-3% Power
1st Main Feed Pump- 2-3% Power
2nd Main Feed Pump- 50% Power
How do the mini-flow valves for the FW pumps work?
FV-1/FV-2
- open and close to maintain 7,000 gpm through MFP to prevent overheating
- Flow goes back to the condenser
During start-up, what is used to spin the FWPT’s?
High pressure Main steam
During normal plant operation what is used to spin the FWPT’s?
Low pressure reheat steam from ‘D’ MSR Line
How do the FWP mini flow valves fail on a loss of air?
Fail open
Which valve must be opened first within the HP control and stop valve arrangement?
The control valve must be closed before the stop valve can be opened.
What controls FWPT speed?
Main FW control system (FWCS)
What does gland seal do for the FW system?
Provides shaft sealing steam to prevent air leakage in and steam leakage out of FWPT’s.
What provides cooling to the FWPT LO coolers?
TCW
What does IA do for the FW system?
Provides IA for AOV’s in system
Air for MFP INPRO oil seals
Describe the FW Pumps
Single stage
Double suction
What controls the inlet of FWP seal water?
PDV-230 (inlet)
Maintains 15 psid across FW pump seals
What controls the outlet of the FWP seal water?
PV-232 (outlet)
Maintains 135 psig seal discharge pressure. Sent to main condenser ‘A’
Why did we go to INPRO oil seals?
Because when we shut down the MFP’s; water was being leaked into the Pump LO system.
After we get a MFP low suction pressure alarm; how long after do the MFP’s trip?
‘A’ pump 15 seconds after low suction alarm
‘B’ 10 seconds after
If we were to manually trip the ‘B’ MFP, what happens?
Reactor Power Cutback will be initiated.
Select CEDM’s will go into core
Reactor power will be reduced to 55%
What is the MFPT turning gear used for?
Cooling down the turbine before shutdown
Pre-start rotation of turbine before steam is admitted
What do the HP/LP stop valves do?
admit or stop steam flow to the turbine
What do the HP/LP control valves do?
Throttle steam flow to control turbine speed
How many stages does the FWPT have?
Six stages
Why does each stop valve have an above and below seat drain connection?
To remove condensate so it does not flow into the FWPT, which could damage or overspeed the turbine. Drain valves are operated from CR. Sends condensate to the condenser.
What are the FWPT trips?
Overspeed- 6350 RPM Low Suct. Pressure- 245 psig High discharge pressure- 1780 psig Low vacuum condenser-13.5 HgA Low control oil pressure- 75 psig Act/Inactive thrust bearing oil pressure high- 40 psig FW pump bearing low oil pressure- 4 psig Turbine bearing low oil pressure- 4 psig Manual
What happens if both MFPT’s trip?
Reactor trip due to low SG water level and the Aux feed system would be used to maintain SG water level.
What is the purpose of the FWP/T LO system?
Provide lubricating oil to the bearings of the FWP/T
Supply control oil to the FWPT control system
How do the foxboro controllers for the FW mini flow work? (output of controller to valve position)
Full output- Valves Close
Minimum output- Valves open
What do the mini-flow valves do when MFWPT LO pressure is under 75 psig?
They will go closed and remain closed. This prevents bearing and shaft damage
If the mini-flow valve controller loses IA, what position do the valves fail in?
Open
If the mini-flow valve controller loses 125 VDC, what position do the valves fail in?
Unchanged; but if MFWPT is tripped, valve will open. This is due to the fact that actual flow is less then the controllers set-point. Therefore the controller sends an output signal to the valves.
If the mini-flow valve controller loses 120 VAC, what happens?
Valves fail open; but if MFWPT trips, 125 VDC solenoid will close the valves.
What is the heat rise across the HP FW heaters?
About 100 degrees F across a string.
Why do the FW pumps and heaters discharge into a common header?
Ensure mixing for equal temperatures to both SG’s
If we have 1 HP FW heater string out of service what is our MW limit?
1109 MW
If we have 2 HP FW heater strings out of service what is our MW limit?
326 MW
If we have 1 LP and 1 HP FW heater string out of service what is our MW limit?
978 MW
Describe the FWP lube oil pumps?
- Each FWP has 2 A/C driven LO pumps
- 1 running and 1 in standby
- Each pump has two discharges
Describe the 2 discharges of the FWP lube oil pumps.
One for LP header, 55 psig to the bearings
One for HP header, 200 psig for control
When will the standby FWP lube oil pump auto-start?
Approx. 195 psig
Where is the emergency lube oil pump powered from?
NKN-M46. Supplies LO to the bearings only
Describe the HP stop valves
- Hydraulically positioned valves that close quickly when tripped. Above/below seat drain connections (for prestart removal of condensate.)
When will the MFWP TG start?
Placed to start and the following;
- Sufficient TG motor oil pressure
- No electrical fault present
- starts/engages around 2 rpm
Where is the MFWP TG geared to?
LP end of the turbine rotor
What is long path recirc used for?
- Clean up secondary prior to feeding SG’s
- Secondary system chem injection points
- Method for cooling FW heaters following unit trip when FW pumps are not running.
What happens when a MFWPT trips?
- HP/LP stop and control valves close
- Mini-flow control valves close
- FP trip signal to RPCB
- CR annunicator
What is the normal FWPT control oil system pressure?
220 psig
When will the standby main oil pump auto start?
195 psig
At what FWPT control oil system pressure will the FWPT trip?
75 psig
What is the normal thrust bearing wear device supply pressure?
62 psig
What is the FWPT trip pressure of the thrust bearing wear device supply?
40 psig
What is the normal oil filter outlet pressure?
57 psig
When does the Emergency oil pump autostart?
37 psig
What is the normal pressure of the turbine and pump bearings header pressure?
12 psig. FWPT trip at 4 psig on either one.
Explain long path recirc.
Cleanup secondary plant before putting water into the steam generators. One CD pump thru demins, thru LPFW htr’s, bypass MFP and either bypass of thru HPFW htr. Recirc back to the condenser thru HV-46 or HV-31.
Explain the LP control valve assembly.
Has two lift rods, a lift beam, and five valve assemblies
Describe the sequence of speed control for the FWPT.
The feedwater control system sends signals to the speed governor which sends signals to the operating cylinder which controls the 5 low pressure control valves and 1 high pressure control valve
What helps remove moisture and air from inside the lube oil reservoir?
FWPT vapor extractors run continuously while turbine is operating
What is the normal operating speed of the FWPT?
4400-5774 RPM
What is the purpose of the FWP turning gear?
Prevent bowing of the rotor
Explain the orientation of the HP stop and control valve?
They are in a common housing
Explain the LP control valves and their operation
- 5 single lift, spherical seated valve assembly’s
- the beam lifts the valves in sequence to control the flow of the LP steam into the turbine
- If the last LP control valve is fully opened, then the HP control valve will be opened by the same beam to help supplement flow.
What happens to the control valves (LP and HP); when the MFPT trips?
They are closed. To prevent an uncontrolled start, which could occur since on a turbine trip reset the hp/lp stop valves go wide open.
What is MFWPT speed determined by?
The relative position of the LP/HP control valves. The position are determined by the operating cylinder. The operating cylinder is controlled by the speed governor. The speed governor responds to speed demand from the DFWCS or from the manual speed control potentionmeter in the control room.
Explain the FW pumps.
- Single-stage, horizontal with double suction impeller
- 20,000 gpm, 350 degrees F at discharge
What are the valves we use for long path recirc? Where are they?
HV-46 and VA-31.
46- TB Southwest above hydrazine day tank
31- TB under MFWP ‘B’
When would we use VA-31?
All low flow rate operation during plant shutdown. This is to prevent water hammer during heater cool-down.
When the control room asks if the green light is lit; what are they doing?
- Green light means that the HP control valve is closed
- Tells the operator that the HP stop valve test circuit is enabled
- When the test push-button is pushed the stop valve closes and reopens.
Between the HP stop/control valve; which valve must be closed for the other valve to open? Why?
The control valve must be closed before the stop valve can be opened. Because the HP stop valve doesn’t have the ability to open again a large delta-p.
