Feedwater Level Control Flashcards
What is the purpose of the Feedwater Level Control System?
Control, automatically or manually, the flow of feedwater to RPC to maintain within limits
How are the RPV water level limits determined?
Determined by requirements of steam separators to limit moisture carryover.
Where is RPV Instrument 0?
bottom of Moisture Separators
What is moisture carryover?
moisture remaining in steam following steam dryer, due to high reactor level, and going to turbine. can cause damage to turbine blades, pipe erosion and increased radiation levels
What is Moisture carry under?
Steam from moisture separator entrained in downcomer flow - caused by low water level in vessel - which may cause decreased core sub-cooling and possible jet pump and RR Pp cavitation
What sets of instruments provide input to FWLC?
RPV Level; Steam Flow; Feedwater Flow
What channels provide RPV Level for FWLC?
A & B Narrow Range; A Medium Range
What does the FWLC logic do if a RPF is off?
When RFP light is lit green (Pp Off) flow transmitter is remvoed from measurement circuit and zero flow signal inserted; therefore, no flow can be detected unless Pump is on or Control switch in PTL
What are the alarms for FWLC input transmitters?
Level instrumentation deviation
RFP suction transmitters or Steam Wide Range Transmitters compared to eachr other and if deviation greater than 12psig
How many FRVs are tehre?
3 - 2 main and 1 low flow reg valve
What kind of valves are teh main FWRVs?
AO drag valves to improve throttling.
What will cause FWRV lockup?
Low instrument air pressure or blown fuse or dual position solenoid failure
What provides backup to the normal FWRV IA supply?
Backup nitrogen bottles supplied for approx. 30 minutes
At what pressure does the FWRV’s lockup?
65psig IA
When does the backup N2 valve in?
~83psig
What is the flow rate for the LFRV?
U2 - 11% (6in) ; U3 - 23% (8in)
What will cause a lockup of the LFRV?
45psig IA or Blown Fuse
How is FRV Lockup cleared?
Clear the signal and press reset button on 5 panel
What positions the FRV?
2 24 VDC powered valves (normally de-energize), pressure switch and an LVDT
What methods of control are available for the FWRV?
Automatic Single element, Automatic 3 element, Individual valve control, Manual Bypass
For the FWRV What is Manual bypas mode?
Entered manually by pullying control station out of panel and toggle switch to bypass -
level can be controlled by depressing individual or low flow control station out buttons (only second detent is available 20%/sec)
For FWRV, What auto puts you in manual bypass mode?
loss of communication or digital control station output fails
What are teh options for controlling the FWRV in manual mode?
1st detent - slow - 2% per second
2nd detent - fast - 20% per second
In FWRV Single Element Control, what element is monitored?
Rx Water Level
At what parameter limit is FWRV Single element control automatically entered?
Steam flow less than 29%;
Rx Scram
Setpoint Setdown
How does the FWRV Single ELement Control function?
Measures the deviation between the actual level and the desired level and causes the master control stations output to change
What parameter limit is needed for FWRV Three Element Control?
Steam Flow >33.5% and Auto P/B depressed
What is monitored/compared for FWRV Three element control?
Steam flow, feedwater flow, and reactor water level
When will Low FRV transfer to Main FRV?
LFRV 85% Open; OR
Steam flow greater than 28%; OR
Either Main FRV >15% open
What is the limit on demand for opening the A FRV?
THe A FRV will not open unless feed water demand reaches 3%
What is the sequence for Opening FWRV on startup?
Feedwater demand is met by LFRV with mains closed until demand signal reaches 3%, then A FWRV is allowed to open. As A opens, LFRV closes.
Power is increased until 40% when Master Controller undergoes bumpless transfer to 3 element control
Steam flow increases to 50% and (by procedure) B FRV can be opened manually. At 5% it is placed in auto. As B opens, A starts to close until they are supplying equal feed flow
What is the FRV operation on shutdown?
Before Total FW Flow reaches 5Mlbm/hr, one FRV should be placed in manual and closed.
When total steam flow drops to 29%, Master Controller transfers to single element control
LFRV will open and control level if:
Total STEAM FLOW less than 28%; AND
A&B FRV less than 10%; AND
Both LFRV and Master controllers are in auto
At what points does the Master Controller transfer between single element and 3 element control?
Steam Flow > 33.5% transfers from single to 3. Steam flow <29% swaps from 3 to single
What causes the CB Min flow valve to lock up?
Loss of IA (<65psig) or Blown Fuse
What causes the CB Min Flow Valve to Open automatically?
Start of first CB Pump sends 100% demand signal to valve for 20 sec, then lowers demand to 80%.
It is ramped open if:
One CB Pump indicates low amps for 4 sec. AND
None of the other pumps show high amps AND
RFP suction pressure is not low (200psig)
What will cause the CB Min Flow Valve to close?
CB Pumps indicated high amps (>255amps) for 20 seconds
RFP suction pressure low (200psig) with feed pump in service for greater than 15 sec and recirc valve open greater than 5%
RFP suction pressure 20psig less than Wide Range RPV pressure AND no RFP running AND RPV <400psig
Last CB secured
For FWLC Level Signal - selection lights - what is the meaning of the backlighting colors?
White indicates level signal selected by FWLC
Amber indicates level signal not available
Flashing Amber indicates level signal that was selected by operator but is no longer selected by FWLC
What is the order of switching FWLC Rx Level Signal if bad quality signal is detected?
NAB MA (Narrow A, then B, Then Medium A
When is the second FRV put in service?
> 5Mlbm/hr
When will FRV transfer to LFRV?
On shutdown:
at <5Mlbm/hr 2nd FRV removed from service;
Transfer when both FRV <10% open
How does Setpoint Setdown respond when the FRV Master Controller is in Manual?
It will NOT respond automatically
When does the Master Control Station transfer from Auto to Manual?
Rx Water level inputs Bad Quality OR
Both A & B individual controls put in Manual
When do individual FRV stations transfer to Manual?
Deviation >10% between demand and actual position Position signal is bad quality; valve lock up Manual bypass valve or valve position is in test
What is FRV Controller tracking?
If LVDT fails on one valve, taht valve goes to manual and the other valve goes into trackign mode for 2 seconds where it freezes what is happening and then is released to go to the setpoint
What initiates Setpoint Setdown?
SCRAM or 2/3 level instruments <0”;
MASTER CONTROLLER MUST BE IN AUTO
How does Setpoint Setdown Operate?
T-0
FWLC system setpoint taken to -10” and locks FRVs in place for 1 sec, transfers to single element
T-1
Looks to see if level > -30”
Yes: system pulses FRV to 30% of current demand;
No: system releases FRV to control at -10”
T-25
Controller released to control at -10”
T-45
Level setpoint ramped back up to original value at 10”/min
(setpoint on LFRV will show original setpoint (typ. +30”))
What is RR Runback (EPU)?
If >9.8Mlbm/hr Steam Flow AND
<3RFPs AND <25” level; OR
<4C/CB Pps AND >10.3Mlbm/hr FW Flow:
RR Pumps Runback to 68% speed (70% flow)
What is the Max FW Flow Limiter?
Designed to prevent RFP damage due to high motor amps - uses bkr contacts and flow measurements to limit amps.
What is the MCR backlighting scheme for FWLC?
No backlight - level signal available but not selected
White - level signal selected
Amber - level signal not available
flashing Amber - level signal was selected by operator but is NO
LONGER available
What happens if ALL 3 FWLC level sensors go bad?
Master station transfers to manual and will be reading off MR-A.
What provides power to FWLC?
Bailey is supplied power from ESS & IB -
4 power supplies - only 2 are required.
