Feedwater (FW) Flashcards
What is the main purpose for the Feedwater system ?
-Provides Feedwater at proper pressure,temperature, & flowrate during all modes of operation
-Provide Recirc path back to Main Condenser for Feedwater cleanup during secondary startup & shutdown
What pressure do the Feedwater pumps discharge into the steam generators ?
Feedwater pumps raises condensate from 350psig to 1200psig to allow flow to go into steam generators
What does the Feedwater pump double suction arrangement provide for the pumps seals ?
Allows 350psig of suction pressure to be felt on pump shaft seals, rather than the 1200psig discharge pressure
What is controls the Feedwater flow rate ?
-Flow is determined by speed of MFWP Turbine
What does the Digital Feedwater Control system do? How does it work ?
Controls Speed of MFWP turbine which is determined by Steam Generator water level
How much flow does each MFWP provide at power ?
Each pump delivers 62% of total required flow at rated power
Where are the MFWP shaft seals receive seal water from ?
Supplied with seal water from Condensate Pump discharge header
Why is instrument air supplied to MFWP bearing oil seals ?
-Keeps water out of seals
-Keep airborne particulate out of seals
-Prevents oil from leaking out of seals
What do the MFWP Mini-flow Recirc Control Valves do?
Maintain at least 5,000 gpm through the pump to prevent overheating
What determines the MFWP Miniflow Valves positions ?
It’s based on the flow rate going to the MFWP
What is the collar device used for on the MFWP Miniflow valve stems ?
Doesn’t allow valve to open all the way which limits flow through Miniflow valves limits to 5000gpm
How do the Mini-flow valves use ?
Reverse acting that is spring loaded to open & uses air to close the valves
What does the Flow Transmitter do ? How does it work?
-Sense flow at suction of pump which sends electrical signal to Flow Indicating Controller
What does the Flow Indicating Controllers(FIC) do for the MFWP Miniflow valves ?
FIC receives signal from flow transmitter & then position a Flow Relay that controls air supply to Mini flow valve
How do the solenoid operated valves control air supply going to MFWP Mini-flow valves actuator ?
Solenoid Valve allows air to pass,stop it, or vent line to position mini flow based on detected flow
What position are the Solenoid Valves normally in ?
Solenoid valves normally deenergize which allows air from Flow Relay to pass through mini-flow valve
What does the MFWP Miniflow valve close & open ?
-When flow through pump is <5000gpm FIC positions Flow Relay to align valve to open mini flow valve to maintain at least 5000gpm to the ‘A’ Condenser
-Will close mini flow valve when flow rises above 5000gpm
When does the MFWP Mini Flow Normally open ?
This happens when:
-MFWP discharge valve is closed
-Feedwater isolation valve closes
-Low power operations
-Following Reactor Trip
What happens on a low lube oil pressure to the Feedwater pump/ turbine ? How do the mini flow solenoid valves reposition ?
-The pump/turbine will trip
-Solenoid valve will supply air to top of valve and port air from bottom of it to CLOSE the Mini-Flow valve
Why does the MFWP Mini-Flow valve supposed to close, when there is low lube oil pressure to MFWP & pump trips ?
-Mini flow valve will close to prevent pump from freewheeling from condensate flow while pump is idle
-Don’t want freewheeling while there’s low lube oil pressure to protect bearing
What happens to MFWP Mini-Flow on loss of instrument air ?
Mini flow valves fail OPEN on loss of instrument air
What happens to mini flow valve on loss of 120VAC power from its MCC D-Panel ?
-Flow Indicating Controller will lose power, which makes FIC output go to ‘zero’
-Since it fails to “zero flow” it’ll make mini flow valve open
What happens on loss of 125VDC control power to the solenoid operated valves for mini flow valves during NORMAL OPERATION?
During normal operation nothing will happen since solenoid valves are normally deenergized
What happens on Feedwater pump trip due to loss of lube oil followed by loss of 125VDC to solenoid valves ?
-Loss of NK to solenoid valves fails to there normal deenergized state
-Since MFWP turbine is tripped FIC will sense low flow going through pump which will open mini flow valve
-This is bad for bearings during a low lube oil pressure trip
Why is seal water used on MFWP ?
Used to stop Feedwater from leaking out of pump shaft & limit oxygen in leakage
Where is the seal water supplied from? How are the pump seals protected from damage from foreign solids ?
-Supplied from condenser header
-2 y-strainers protect seals from damage (1strainer in service,other in standby)
What do the Gland Seal Regulators do ?
DP Controllers send signal to these valves to maintain 20PSID across MFWP Pump seals
How is the MFWP Seal Water directed into the pump ?
Flows along pump shaft to the leak off section in pump section
What’re the two flow paths for the MFWP Seal Water leak off ?
-Seal water can exit pump via Gland Leak off piping & flows through Gland Leak-Off Regulator
-Some exits will drip out of pump shaft packing & is directed to Steam Packing Exhauster Drain Tank
What do the Gland Leakoff Regulators do?
Pressure indicating controllers will sense Pump Gland Seal Discharge & will adjust these valves to maintain 135psig Gland Leakoff Back Pressure
Where does the Seal Water exit to ?
Seal water will be sent to ‘A’ Main Condenser
What’re the HPFWH used for ?
Preheat Feedwater to reduce thermal stress on the SGs & improve plant efficiency
What’re the inlet and outlet temperatures for the HPFWH?
Inlet temperature to the #5HPFWH is 350F & outlet temperature from #7HPFWH is 450F
How many HPFWH Strings are in service at a time ?
Both strings of HPFWH strings are normally in service with open inlet & outlet MOVs
What is the HP Feedwater Train Bypass line used for ?
Bypass line supplies capability of operating with one HPFWH string out of service
How does the HPFW Train Bypass line work ?
Normally maintained close, when opened passes 25% of total FW flow
How foes 480VAC MCC (NH)binterface with the Feedwater system ?
480VAC provides power to Feedwater MOVs
What does the 480VAC MCC DPanel provide power to ?
Provides 120VAC to MFWP Mini Flow Valve Flow Indicating Controllers
How does 120VAC(NN) interface with Feedwater system ?
Provides power to Feedwater Pump Turbine Controller in SSR Room, which position Feedwater Pump Turbine Control Valves to regulate Feedwater Pump Speed
How does the condensate system interface with the Feedwater system ?
-CD provides MFWP suctions
-CD provides water to pump seals via condensate header
-CD provides return path for Mini flow Recirc & long path Recirc
-CD provides exhaust & drain for:
FWP Turbine exhaust
FWP Turbine Drains
Steam line drains
Provides exhaust vacuum
What happens to Feedwater system on loss NNN-D15 or D-16 ?
-Results in FWP Turbine Control Valves drifting close slowing down to 300rpm
-When this happens it WONT trip the pump it result in Reactor Power Cutback
What will happen on loss of one Condensate Pump ?
-Will cause low suction pressure at ‘B’ MFWP, which will trip pump after 10seconds
-Once ‘B’ MFWP trips it’ll prevent, ‘A’ MFWP to not trip on low suction pressure
What will happen on a loss of two condensate pumps ?
-Will cause low suction pressure on ‘B’ MFWP, trips after 10 seconds
-‘A’ MFWP suction pressure will rise,but not enough past low suction setpoint & will trip after 15 seconds
How will loss of Extraction Steam & Drain affect Feedwater system ?
Loss of extraction steam to Feedwater heater would reduce thermal efficiency
How does loss instrument air affect Feedwater system ?
-MFWP Mini-Flow Recirc will go open
Loss of service air to MFWP Bearing:
-Oil leak from bearing
-Airborne particulate entering bearing
-Allow water from Gland sealing steam packing exhaust drain tank
What would happen on loss of Digital Feedwater Control System ?
Results inability to control Feedwater & loss of automatic MFWP speed control, could result in reactor trip to SG Low LVL
During plant startup what operations do the condensate/Feedwater systems operate in ?
Placed in long path Recirc until water chemistry is right
What must be in service prior to starting the Main Feedwater Pump?
Main Feedwater Pump Turbine must be placed in service by placing in Hot Standby per procedure
When is the first Main Feedwater Pump started ?
Started prior to exceeding 3% power which is the capacity of one Aux. Feedwater Pump
What happens to the Aux. Feedwater Pump when a Main Feedwater Pump pressurizes the Main Feedwater Line ?
Once main Feedwater pump is started the Aux. Feedwater Pumps are stopped
When do the second Main Feedwater Pumps start ?
Plant operates with one pump up to 50% power, then 2nd pump is started
What power level can one Main Feedwater Pump be shutdown at ?
If plant load decreases below 62%
What does it mean when the Feedwater Pump & Turbine are in standby ?
Standby condition is maintained in warned & ready condition
During plant shutdown when do the Feedwater pumps need to be stopped ?
-Stopped when the MFWP cause excess RCS cooling
When does the Aux Feedwater Pump takeover during plant shutdown ?
Once MFWP cause excess RCS cooling, the Aux Feedwater Pump must be used to maintain SG Level
After a shutdown what flow path is the Main Feedwater system placed in?
Main Feedwater system is placed in long path Recirc for shutdown chemistry control & system shutdown
What happens on a loss of one MFWP ?
Reactor power cutback will initiate and reduce Reactor & Turbine power to the capacity of one MFWP
What will happen on a loss of both MFWPs ?
Will trip reactor on low SG Level & SG Level will have to be maintain by Aux. Feedwater system
