Systems Exam 4 - Auxiliary Feedwater Flashcards
(26 cards)
What is used for AFW when the CST is empty?
→normal is SSW if CST Level <6%, unit is in ERGs, and with Shift Man approval
→if SSW is unavailable, then provisions provided to fill CST with Fire Protection water
What happens to U2 Main Feed on an AFW Pump start?
→FSBV closes on AFW Pump Start
→U2 AFW connects to MFW before CTMT penetration, same line used by FSBV and AFW to feed SG
Aux Feed Design
→designed to cool down RCS from 557°F to 350°F for RHR use
→can provide normal cooling load up to 7% RTP
FRS-0.1 Aux Feed flow requirements
→response to ATWT
→AFW is required to be >860 gpm to ensure sufficient decay heat removal
→normally 460 gpm is sufficient since normal S/D decay heat is lower
ABN-803 (Control Room Evacuation) Actions
TDAFWP is tripped on the MCB to prevent overfeeding the SGs when a SFGDs Bus is deenergized at the RSP.
Motor Driven Aux Feed Pump capacity and shut off head
570 gpm at a maximum developed head of 1370 psig
Motor Driven Aux Feed Pump Recirc Valves 2456 & 2457
→minimum flow recirc line with orifice 200gpm
→close on >200gpm
→open <227gpm
→fail open on loss of air or power
→normally maintained open in standby
→common line back to CST
→valves have an accumulator to allow 2 strokesfor 30 mins(from same air accumulator as MDAFW Pump flow control valves)
Motor Driven Aux Feed FCV Accumulator design
Each associated flow control valve provided with a safety class air accumulator sized for five full cycles, plus leakage and steady state consumption for 30 minutes (same accumulator as recirc valves).
MDAFW Pump Flow Control Valves
→normally open AOVs
→fail open on loss of air or power
→PV‐2453A & 2453B for train A to SGs 1 & 2
→PV‐2454A & 2454B for train B to SGs 3 & 4
→air accumulators for 5 full cycles for 30 minutes (shared accumulator with pump min flow valve)
→on start of MDAFW Pumps, M/A stations trip to auto and go 100% open
→after 10 sec time delay, manual operation can be selected
→each feed line has an orifice to limit flow to 700 gpm
Turbine Driven AFW Pump
→1145 gpm at 4075 rpm and a maximum developed head of 3236 ft (1433 psig)
→overspeed occurs at 4750 ± 50 rpm (116% rated speed)
→overspeed mechanism will reset itself at 3000 rpm
→Trip & Throttle Valve will need to be locally reset
→on loss of air or electrical power, turbine speed governor will fail to max speed
TDAFW Pump Steam Supply
→supplied by Main Steam lines #1 & #4 before MSIVs
→normally closed AOVs with accumulators to allow isolation on loss of air
→accumulators allow isolation within 30 mins + 7 more hrs to keep valves closed
→valves fail open to ensure turbine acceleration to rated speed in 85 sec
Turbine Driven AFW Pump Local Control Panel
→powered from 125VDC uED1‐1
→local panel shows valve position T&TV and turbine speed
→SI on Train A removes control power to local panel
→prevents the following remote indication and control (on MCB):
→indication of turbine speed
→turbine overspeed light indication
→no annunciator for turbine overspeed
→T&TV position indication
→cannot trip the turbine from the control room
→turbine will still start and come up to speed, just without indication
→can locally trip pump OR close steam supply valves from MCB to stop the turbine
→power to local control panel can be restored after SI on Train A is reset by depressing OPEN push button 2452H on CB‐09
→this restores full functionality of the turbine
ABN-305
Per ABN-305, once TDAFWP trip issue is fixed u-SK-2452A is adjusted to 0% prior to opening the T/T valve and at this time the speed will go to 2000 rpm and can be adjusted by the operator
Turbine Driven Pump FCV Accumulator design
Each associated flow control valve provided with a safety class air accumulator sized for five full cycles, plus leakage and steady state consumption for 30 minutes
AFW CNTMT Isolation MOVs
→each SG has ONE handswitch that controls BOTH the MDAFW & TDAFW MOV isolation valves
→MOVs powered from opposite train from FCVs
→opposite train power supplies ensure that we can still isolate flow to an SG on loss of one train
CST Design Criteria
→500,000 gal tank
→53% (244,000 or 249,100 gals, depending on reference given) reserved for AFW per revised TS 6-30-2011
→10-inch line to suction of both MDAFW pumps
→a second 10-inch line to suction of TDAFW pump
→CST minimum volume (53%) ensures that water is available to maintain the RCS in Hot Standby for 4 hours followed by a cooldown to 350°F at a rate of 50°F/hr for 5 hours
TDAFW Pump Auto Starts
BLA
→B - Blackout-OL opens MS supply valves #1, B Train; #4, A Train
→L - Lo-Lo Level 38% U1, 35.4% U2 in 2 SGs (2/4 Level Transmitters)
→A - AMSAC
“There’s no T in turbine.”
MDAFW Pump Auto Starts
BLAST
→B - Blackout (Train related)
→L - Lo-Lo Level 38% U1, 35.4% U2 in 1 SG (2/4 Level Transmitters)
→A - AMSAC
→S - SI in conjunction w/ SI Sequencer
→T - Trip of both Main Feed Pumps
AFW Auto Start Plant Response
→SG Blowdown isolates
→SG Sampling isolates
→CST discharge valves HV-2484/2485 (Makeup/Reject Valves) close
→Split Flow Bypass Valves (U2 only) close
→Motor Driven AFW flow control valve trip to Auto 100% open
How to reset the trip and throttle valve:
1) Manually reset the overspeed trip linkage by physically repositioning the trip linkage. The overspeed device plunger mounted on top of the turbine bearing casing should drop back into the plunger housing.
2) Depress clutch lever to engage handwheel. Clutch must remain depressed through steps 3 and 4 below.
3) Turn handwheel CW until the latch mechanism is fully engaged.
4) After latch mechanism is fully engaged, turn handwheel CCW until actuator is fully up.
5) Release the clutch lever.
Note: the turbine on the TDAFW pump must be at rest for 15 seconds before resetting governor speed setting
What is the minimum recirc flow for the TDAFW Pump?
→130 gpm on mini flow line
→limited to 20 min to prevent pump damage
What controls are available for AFW at the RSP?
→TDAFW speed control and BOTH steam supplies
→both MDAFW pump breakers
→FCVs to all four SGs from MDAFW and TDAFW pumps
→M/A stations on RSP set in Auto allow MCB operation of FCVs from MDAFW and TDAFW Pumps to all 4 SGs
What happens if AFW actuates at power with no additional operator actions?
Power Excursion. We send cold water to the SGs, which needs to be heated up, raising Rx power without additional steam demand.
Operator response is to lower load by 50 MWe.
MFP trip signals energize to actuate. How do we keep from starting AFW when shutting down and tripping both MFPs?
→we remove fuses that send MFP trip signals to start MDAFW Pumps
→Train A comes through BOP Aux Relay Rack #1
→Train B comes through BOP Aux Relay Rack #2
