Auxiliary Feedwater & AFAS Flashcards
What are the Aux Feedwater Safety Related Functions?
- Sufficient cooling of the RCS to prevent lifting of the Pressurizer safety valves post trip
- Permit plant C/D to 325F for shutdown cooling entry conditions, assuming a loss of AC power.
- Isolation of AFW steam & Feedwater lines to affected S/G following a MS or feed line break
What are the FSAR requirements associated with Aux Feedwater?
- Secure AFW within {30 min} [10 min] of inadvertent MSSV or ADV opening
- Isolate S/G and commence C/D within 45 min of a SGTR w/ LOOP
- Initiate 75 F / HR cooldown within 1 hour of a LOCA
- Isolate SGBD within 30 min of a total loss of feed event
Describe the Motor Driven AFW Pumps.
UNIT 1
325 GPM @ 1000 psig
75 GPM recirc flow
4160V A3 / B3
Normal: ‘A’ to the ‘A’ S/G; ‘B’ to the ‘B’ S/G
Alternate: Either pump to either S/G using the cross-tie line. Mode 4 and below only
RTGB, HSP, {and local PBs}
Stop / Auto / Start
{Unit 1 switches spring returns to Auto after either Start or Stop}
AFAS-1 signal will start the ‘A’ MDAFW Pump;
AFAS-2 signal will start the ‘B’ MDAFW Pump
If previously running for any reason, they will re-start 15 seconds post EDG breaker closure following a LOOP.
Following a Station Blackout, it is assumed that an AFAS actuation signal could have occurred. To prevent the pumps from auto starting as soon as AC power is restored, the pumps are disabled by:
Taking their Normal / Isolate switches to the “ISOLATE” position.
0-500 GPM flow instruments on MDAFW pump headers after the cross-tie line.
Flow transmitters indicate individual header flow
UNIT 2
275 GPM @ 1000 psig
50 GPM recirc flow
4160V A3 / B3
Normal: ‘A’ to the ‘A’ S/G; ‘B’ to the ‘B’ S/G
Alternate: Either pump to either S/G using the cross-tie line. Mode 4 and below only
RTGB, RSP. and local panel
Stop / Auto / Start
[Unit 2 switches spring returns to Auto after Start, but has a Hard Stop position.]
AFAS-1 signal will start the ‘A’ MDAFW Pump;
AFAS-2 signal will start the ‘B’ MDAFW Pump
If previously running because of an AFAS start signal only, they will re-start 30 seconds post EDG breaker closure following a LOOP.
Following a Station Blackout, it is assumed that an AFAS actuation signal could have occurred. To prevent the pumps from auto starting as soon as AC power is restored, the pumps are disabled by:
Taking their control switch to the “Hard Stop” position.
0-500 GPM flow instruments on MDAFW pump discharge before the cross-tie line.
Flow transmitters indicate pump discharge flow
Describe the C AFW Pump.
UNIT 1
600 GPM @ 1000 psig
100 GPM recirc flow
2000 – 3600 RPM
50 – 1085 psig saturated steam
RTGB & local Pushbutton (Test / Trip)
Closed – Reset / Auto / Start
{Unit 1 switches spring returns to Auto after either Start or Stop}
0-1000 GPM Flow instruments on pump discharge line before the cross-tie line.
They indicate pump discharge flow
Shaft driven Oil Pump cooled by pump flow
No Aux Oil Pump or heater – Portable heaters must be brought in to maintain oil temperature when ambient temp is <80F
Bearing oil temperature:
* >70F normally
* IF oil temperature falls below 60ºF, the C AFW PUMP must be declared OOS and the oil temperature increased either by local manual starting of the turbine or using temporary heaters.
* Do not start <40 F
UNIT 2
570 GPM @ 1000 psig
70 GPM recirc flow
1875 – 3750 RPM
50 – 985 psig saturated steam
RTGB, & RSP
Closed / Open key-switch
0-1000 GPM Flow instruments on pump discharge line before the cross-tie line.
They indicate pump discharge flow
Shaft driven Oil Pump cooled by pump flow
Aux Oil pump and heater maintain lubrication and operability when shutdown
Bearing oil temperature:
* >70F normally
* IF oil temperature falls below 60ºF, the C AFW PUMP must be declared OOS and the oil temperature increased either by local manual starting of the turbine or using temporary heaters.
* Do not start <40 F
Describe C AFW Pump Turbine Trip Throttle Valve auto response on an overspeed.
- Electrical Overspeed device trips closed the TTV at 115% of rated rpm. This will NOT trip the mechanical overspeed trip linkage, and does not require any local operator actions to reset
Trip Hook auto returns to Ready to engage position as soon as overspeed clears at 3000 rpm - Mechanical Overspeed device trips closed the TTV at 125% of rated rpm and latches in. This WILL trip the overspeed trip linkage which will require local action to reset.
Also will operate a limit switch contact to send a signal to the electrical overspeed solenoid to ensure that MV-08-3 will trip.
{On either overspeed trip, MV-08-3 will indicate Dual. Why? Valve position provided from the valve (which is closed) AND the motor limit switches (which is demanded to be open)}
[On either overspeed trip, MV-08-3 will indicate Closed. Why? Indication is from valve only. No input from the motor]
Describe how to Reset C AFW Pump Trip Throttle Valve.
Unit 1
a) Reset Overspeed trip linkage if it was a mechanical trip
b) {Place CS on RTGB-102 in Stop / Reset}
c) Verify no rotation
d) Ensure 3 minutes have elapsed since rotation stopped
OR
Fully cycle the speed control knob CCW, then CW to leave at max speed setting
Failure to do either could result in the pump tripping again following re-start
e) Ensure discharge control valves are closed
f) Start pump by taking RTGB control switch to the “Start” position
Unit 2
a) [Key switch on RTGB to close]
b) Reset Overspeed trip linkage if it was a mechanical trip
c) [Key switch to open]
d) Verify no rotation
e) Ensure 3 minutes have elapsed since rotation stopped
OR
Fully cycle the speed control knob CCW, then CW to leave at max speed setting
Failure to do either could result in the pump tripping again following re-start
f) Ensure discharge control valves are closed
g) Start pump by taking RTGB control switch to the “Open” position
Discuss the power supplies to C AFW Pump Steam Admission valves.
Unit 1
Both valves are powered from the AB DC Bus
Unit 2
(‘A’) MV-08-13 from the ‘B’ DC Bus
(‘B’) MV-08-12 from the ‘A’ DC Bus
Discuss the Unit 2 MDAFW SOVs.
Located prior to cross-tie line and MOV’s
SE-09-2: Powered from the ‘A’ AC Bus
SE-09-3: Powered from the ‘B’ AC Bus
Fail closed on a Loss of Power
Auto open: Train related AFAS signal
Auto close: When NR level ≥ 29%
No throttling capability
All can be operated from RTGB
Can be locally manually operated by removing the pin from the upper stem assembly
Provide Double Isolation Protection against single valve failure to isolate a faulted SG
Discuss Manual SG Level Control with AFAS Signal Present.
Valves can be throttled normally after they have gone full open
If SG level increases to 29% reset level then the valves will go closed
Must depress the 8 (4 per side) AFAS Actuation Reset PBs (after reaching 29%) to regain control of the Aux Feed Valves
* Otherwise valves will continue to cycle open then closed between 19% and 29% level After Rx Trip
Operators typically shut C AFW valves, and throttle A & B valves to get 220 gpm to each SG.
Discuss the Unit 2 TDAFW SOVs.
Located prior to the MOV’s
SE-09-4: Powered from the ‘B’ DC Bus
SE-09-5: Powered from the ‘A’ DC Bus
Fail closed on a Loss of Power
Auto open: Train related AFAS signal
Auto close: When NR level ≥ 29%
No throttling capability
All can be operated from RTGB
Can be locally manually operated by removing the pin from the upper stem assembly
Provide Double Isolation Protection against single valve failure to isolate a faulted SG
Discuss the Condensate Storage Tanks.
UNIT 1
Capacity: 271,200
TS Min: 153,400
Hot standby for one hour, followed by a cooldown to 325 F for shutdown cooling entry
Unit 2
Capacity: 400,000
TS Min: 307,000
U1 Capacity: 130,500
Hot standby for 4 hrs;
AND
4 hr cooldown to 325 for shutdown cooling entry
AND
Still have 130,500 gal of water available for U1
What are the AFAS time Delays?
UNIT 1
≤ 19% S/G NR Level for 235 seconds
UNIT 2
≤ 19% S/G NR Level for 210 seconds
Discuss AFAS Rupture ID Circuit setpoint.
3 out of 4 pressure detectors sense:
A & B S/G D/P ≥ 275 psid
A & B Feed Header D/P ≥ 150 psid
What happens if the D/P that caused the AFAS rupture ID goes away?
The Rupture ID Lockout would clear and AFAS will actuate as designed if a low S/G level condition exists. (including timer)
Discuss AFAS Cycling & Latched Components.
UNIT 1
Cycle
* AFW MOV’s
* Unit 1 MFIV’s do NOT get an AFAS signal
Latched
* AFW Pumps
* Unit 1 Trip / Throttle Valve
* Steam Header Admission Valves
UNIT 2
Cycle
* MOVs & SOVs
* Unit 2 MFIV’s are cycling components that do not cycle. Can re-opened at any time by override
* Can only override AFAS, not MSIS closure
Latched
* AFW Pumps
* TTV does NOT get an AFAS signal – always open
* Steam Header Admission Valves
