Feedwater (FW) Flashcards
What is the purpose of the FW system?
Supply FW from the suction of the FW pumps to the feedwater regulating valves in line to each S/G at the required pressure, temperature, and flow rate
Provide the final three stages of feedwater heating in two parallel heater trains
What is the purpose of the Main Feedwater Pumps?
To provide the motive force to raise the pressure of the supplied condensate from around 350 psig to around 1200 psig to overcome S/G pressure
What type of impellers are utilized on the Main Feedwater Pumps?
Double Suction Impellers
What goes into main feed pump suction?
CD discharge that went through the LPFWH and the HDP discharge
Which FWPT do we start first?
We start FWPT B due to water accumulation in the lube oil reservoir
What system provides lube oil for bearings on the Main Feedwater Pumps?
Steam Generator Feedwater Pump Turbine Lube Oil system
To what capacity are each of the Feed Pumps designed to handle at rated power? What is the procedural limit?
~65% of the total required flow
Procedurally limited to 62% during a downpower to remove one feedwater pump from service
At what pressure does the seal water enter the Feed Pump casing from the Gland Seal Regulator?
150 psig
Where does this seal water come from?
Condensate Seal Water Headers
What is the purpose of the 2 2.5” Y-strainers in the seal water lines?
To protect the feedwater pump seals from damage due to solids
What D/P across the seals is normally maintained by the Gland Seal Regulators?
15 psid
What output pressure do the Gland Leak-off Regulators maintain?
135 psig
What is the purpose of the Mini-flow valves?
To open or close as feedwater flow changes to maintain approximately 5000 gpm through the Main Feedwater Pump to prevent pump over heating
Why does the Mini-flow valve shut when the Main Feedwater Pump trips?
To prevent the pump from freewheeling due to condensate system flow through the mini-flow valve to the condenser
When would the Mini-flow valve be fully open?
When the pump discharge valve is fully shut
How do the Mini-flow valves respond to a loss of IA?
Fail Open
The mini-flow valves use how many air boosters for positioning?
2 (one for opening, one for shutting)
What happens to the Mini-flow valve when Feed Pump turbine lube oil pressure drops below 75 psig? Why?
Go closed
Prevent pump from freewheeling due to feedwater flowing through an idle pump
How are the Mini-flow valves affected by a loss of 120 vac?
Fails open
If the FWPT trips, or is already tripped, the valve will close due to the energization of the DC solenoid
How are the Mini-flow valves affected by a loss of 125 vdc?
Normal ops – no effect
If FWPT is tripped, a loss of DC will result in the valve failing open
How often is the HP Stop valve tested? Any precautions?
Daily
HP Control valve must be closed before testing the stop valve
There’s an interlock which prevents testing of the HP Stop Valve if the HP control valve is open
HP and LP control valves are operated by one hydraulic operating cylinder. Due to mechanical arrangement, which valve opens first?
LP Control Valve
What is the difference between the HP and LP Stop Valves concerning design features?
LP Stop valve has its own valve body and when testing the LP Stop valve it only goes half way closed
Why is there a pressure switch installed on the control oil pressure line?
Acts to close the turbine control valves whenever the feedwater pump turbine is tripped
This prevents an uncontrolled start which could occur since on turbine reset the LP and HP stop valves immediately go wide open
What controls the speed of the Feedwater Pump Turbine? What system is it a part of?
Main Feedwater Control System part of the Reactor Control System
What are the two normal sources of steam to the Feed Pump turbines?
Main steam and reheat steam from the MT system moisture separator reheaters
What is the third source of steam for the Feed Pump turbine?
AS, used during testing
What is the flow path for the Moisture Separator reheater to the Feed Pump?
Flows through the low pressure stop valve and low pressure control valve
What is the flow path for the Main Steam to the Feed Pump?
Flows through the High pressure stop valve and high pressure control valve
Which source is used for normal operation?
Low pressure reheat steam
High Pressure steam is used during startup and to supplement the low pressure system during periods of light MT loads or overload on the feed water pump turbine
What ultimately controls the stop valves and control valves?
FWPT control oil
What system provides shaft sealing steam to A and B FWPTs?
Turbine Steam Seal and Drain System (GS)
What cools the Feed Pump oil system?
TC
Where do the FWPTs exhaust to?
Underneath the reheat trays in the ‘A’ and ‘B’ Condenser sections to the ‘C’ Condenser section
Where are the FWPT drains directed to?
‘A’ and ‘B’ Condenser sections
Where are the Thrust Wear trip and Overspeed trip governors located?
HP end of the rotor and are part of the rotor assembly
Where is the engagement gear for the turning gear located?
Exhaust end of the rotor
What is the normal position of the Turbine Drain Valves under full steam load?
Normally Closed
If the Turbine Drain Valves are closed, how do we remove condensate during normal ops?
They’re provided with a continuous bypass drain line through orifices
What is the purpose of the Feed Pump turning gear?
To provide low speed turning of the turbine rotor for cooling down the turbine before complete shutdown or for prestart rotation of the turbine rotor before steam is admitted to the turbine wheels
What is the interlocked associated with the Feed Pump turning gear and what is it trying to prevent?
Two pressure switches, one monitoring oil pressure on the feedwater pump bearings and the other to monitor the oil pressure to the turbine bearings
A low pressure in either switch will prevent the turning gear motor from operating
This interlock is for bearing protection
Where is the Feed Pump Turning Gear normally operated from?
CR
What are the FWP trips?
- Overspeed 6350 rpm
- Low suction pressure 255 psig after 10
sec - High discharge pressure 1780 psig
- Low vacuum in condenser 13.5” HgA
- Low control oil pressure 75 psig
- Active thrust bearing wear oil high
pressure 40 psig - Inactive thrust bearing wear oil high
pressure 40 psig - FWP bearing low oil pressure 4 psig
- FWPT bearing low oil pressure 4 psig
- Manual in CR or local
What are the three Feedwater Turbine thrust bearing test switches?
Thrust Wear device Test switch
Active Thrust Wear Test Switch
Inactive Thrust wear Test Switch
Describe the operation of the Overspeed Governor
Located on the rotor, there’s a plunger held against its seat in the governor housing by a spring
As the rotor spins faster, the centrifugal force will cause the plunger to move out of the housing, and once it reaches the overspeed setpoint, the plunger will throw out.
When this happens, it strikes the emergency trip mechanism actuating tripper and trips out the turbine
At what nominal setpoint is the mechanical overspeed trip tested to?
110%
What is another way to test out the overspeed without getting up to that speed setpoint?
A jet of oil, controlled by a solenoid valve, can be sprayed into the emergency governor housing to unbalance the plunger and actuate the emergency trip at speeds up to rated
During a startup, when is the first Main Feedwater Pump started?
Prior to exceeding a reactor power of ~3%, which is the capacity of one AFP
When is the second Main Feedwater Pump started?
50% power
Prior to startup, what must be done with the Condensate/Feedwater systems to improve the water quality?
Long Path Recirc
Describe Long Path Recirc
- Prior to shutting down with both FW pumps stopped but still one CD pump
running - Isolate both SG downcomer header and economizer line
- Open both SG cleanup recirc header isolations
- Close FWPT discharge valve
- Unlock and throttle a FWP bypass valve to equalize FW header with the CD
header - Throttle open SGNVA31 long path recirc header bypass isolation to
establish cool down for HPFWH 25-50deg F/min - Throttle closed one of the HPFWH outlet valves to balance cool down
- When HPFW tube side gets down to 200 deg F, open FW recirc to
condense valve and close long path recirc header bypass isolation valve - Adjust MFWP bypass valve to maintain recirc between 8000-9000 by the in
service CD pump - The long path recirc valves are located on the 120’ mezz TB and on the 110’
by the HDT
After each shutdown, why is the Main Feedwater System place in Long Path Recirc?
For shutdown chemistry control and system cooldown
During normal operation, when can I secure one of the Feedwater Pumps?
If plant load decreases below 62%
What will happen if I lose a Feedwater pump while at 100% power?
Reactor power cutback, lowering reactor power and turbine power to within capacity of a single Main Feedwater pump
What will happen if I lose two Feedwater Pumps while at 100% power?
Reactor would trip on low S/G level
S/G level would have to be maintained by Aux feed system
What is some OE on FW?
- Mini flow failed in Unit 1 like a month ago (2/2019) which caused a transient but only went partially closed so the pump did not trip
- FWPT does not like going on the turning gear or getting off
- Some one put their finger over the air port on the FW reg valve causing it to isolate feedwater tripping unit 3
- The pumps have trouble tripping due to all the varnish build up
- The linkage on the high pressure and low pressure stop/control valves may come apart and wont move the valve as it should
