Condensate and Feedwater Flashcards
What are the functions of the Condensate System?
Functions
* Provide deaerated water to the S/Gs to remove heat from the reactor, during normal, shutdown and transient conditions.
* Increase cycle efficiency through the use of the Feedwater Heater, Vents and Drains System.
* Additionally, preheating the feedwater ensures that the S/G tubes or vessel walls are not subject to thermal shock during normal operation
Additional functions:
* Provide seal and cooling water to plant auxiliaries.
* Provide water for S/G initial fill and wet layup.
* Provide for condensate polishing.
* Serve as a cooling media for the gland steam and steam jet air ejector condensers.
* Condensate system is not safety related, except for the CST
* The Heater Vent and Drain System is not safety related.
What is the Condensate/Feed System Normal Flowpath?
From the condenser hotwells → Through (two) running condensate pumps → Through the steam jet air ejector and gland steam condensers → Through the tube side of low pressure heaters 1A & 1B, 2A & 2B, 3A & 3B → Through the tube side of the A & B drain coolers → Through the tube side of low pressure heaters 4A & 4B → To the feedwater pumps, then → Through the tube side of 5A & 5B high pressure heaters →Through the feed regulating valves and feedwater isolation valves to the S/Gs.
The heater drain pumps (HDPs) take suction from the shell side of the A & B drain coolers, and return the condensed extraction steam to the inlet of the #4 FW heater (which is just upstream of the MFW pumps).
Discuss Condensate Storage Tank Tech Specs.
Unit 1
153,400 gallons
Hot Standby for 1 hour followed by cooldown to 325
A loss of condenser vacuum could occur if the CST level drops to 19’ (~160,000) gal. This is the level at which the makeup spray line is uncovered
Unit 2
307,000 gallons
Hot Standby for 4 hours followed by cooldown to 325F and includes 130,500 gal for Unit 1
Procedurally, the Unit 2 CST can supply the U1 CST for purpose of AFW system operability
A loss of condenser vacuum could occur if the CST level drops to 33’ (~300,000 gal). This is the level at which the makeup spray line is uncovered
Discuss Condenser Hotwells.
Hotwell contains enough volume for 4 minutes full power operation
Condenser steam space and hotwells are connected by an Equalizing Line
Hotwell level > 3’8” (44”) can restrict steam flow to the underside of the tubes and can cause rapid increases in condenser back pressure.
Unit 1
1A and 1B Condensate Pumps are each supplied by two 26-inch hotwell outlet pipes. The 1C Condensate Pump is supplied by one of two 24-inch hotwell outlet pipes either from the A or B hotwell
Unit 2
The Unit 2 hotwell outlet pipes (two 26-inch pipes from the A hotwell, and two 26-inch pipes from B hotwell) connect to a common suction header which supplies the 2A, 2B & 2C Condensate Pumps
Discuss Hotwell Level Control.
During normal operation, after processing, both Unit 1 & 2 S/G blowdown flow is directed to the Monitor Storage Tanks in the S/G Blowdown Treatment Facility (SGBTF). The water in these tanks is then returned to Unit 1 & Unit 2 condensers by the use of a pump and vacuum drag through valves {V31189} & [V31190] (Blowdown Return to {1B} [2B] Condenser).
Hotwell Level is monitored on each RTGB and an operator is dispatched to adjust either valve to maintain respective hotwell level . This valve is closed as part of Standard Post Trip Actions.
Currently, the valves are adjusted such that the Unit 1 hotwell level is maintained stable using the majority of return from from the MST and the Unit 2 hotwell is maintained using the remaining blowdown return flow plus auto make-up spray flow from the CST.
Because both Unit 1 and Unit 2 vacuum drag is supplied by a common header, caution must be used when manipulating these valves when either unit condenser vacuum changes.
Discuss Automatic Hotwell Level Control.
Automatic Hotwell Level Control is provided by:
a) Four normal (3”) make-up spray valves associated with each condenser section
b) One large (8”) make-up valve to the 1A condenser
c) One hotwell reject valve to return water to the CST upon a high hotwell level
* The normal make-up spray valves return above the normal condenser water level to allow deaeration of fluid.
* The large make-up taps in below water level, therefore no deaeration occurs.
* When the large make-up valve auto opens, it provides an eight-inch line of mass makeup to the 1A condenser from the CST via piping that can include or bypass the Condensate Transfer Pump.
* The Large M/U Valve and Reject Valve back to the CST are normally isolated for chemistry – O2)
* All AOV’s fail closed, therefore a loss of air results in a loss of normal vacuum drag makeup
Discuss Automatic Hotwell Level Control Setpoints.
Decreasing Level
* First M/U valve opens (LCV 12-1A1) @ - 1”
* Second M/U valve opens (LCV 12-1B1) @ - 2”
* Last 2 M/U valves opens (LCV 1A2 & 1B2) @ - 3”
* Large M/U Valve opens (LCV-12-4) @ - 4” (Currently Isolated)
* Low level alarm @ {-12} [-9] (Both A & B hotwells)
Increasing Level
* Normal M/U valve closes (LCV 12-1A1) @ 0”
* Normal M/U valve closes (LCV 12-1B1) @ - 1”
* Normal M/U valves close (LCV 12-1A2 & 1B2) @ - 2”
* Large M/U Valve closes (LCV-12-4) @ + 2” (Currently Isolated)
* Reject Valve opens (LCV-12-5) & HLA @ + 9” (Currently Isolated)
* Alarm @ +9” (‘B’ Hotwell Only)
Discuss Condenser Vacuum Indications.
Unit 1
Backpressure indicator on RTGB 101,
Condenser backpressure on DEH Ovation Display
Unit 2
Digital Readout on RTGB 201
‘A’ Condenser wide-range backpressure on RTGB 201
‘A’ Condenser narrow-range backpressure on RTGB 201
‘B’ Condenser backpressure on RTGB 201
Condenser backpressure on DEH Ovation Dsiplay
3 local pressure instruments located on the mezz deck
Discuss Main Condenser Vacuum Breakers.
- Manually operated Motor Operated Valves used to break main condenser vacuum
- Loop seals filled by Demin water to ensure no air in-leakage
- No automatic functions
Discuss Condensate Transfer Pumps.
1 for each Unit
Provides the following:
a) Hotwell makeup from CST (thru MUV’s and LCV 12-4) when no vacuum is present
b) Supplies B/U Seal Water to Cond Pumps
c) {Unit 1 condensate transfer pump also supplies water to the condensate polisher for backwash}
d) [The Unit 2 condensate transfer pump can transfer water from Unit 2 to Unit 1 CST for purpose of supplying AFW.]
* Controlled from the RTGB, Located outside near the CST
* The condensate transfer pumps are 5 HP motor driven centrifugal pumps, powered from 480 VAC MCC 1A1 [2A1] and can pump 200 gpm at 22 psig.
Discuss Condensate Pumps.
- Three pumps on each Unit. Two Pumps operate in parallel (A & B); the 3rd (C) is a spare that cannot be immediately started on a loss of one pump due to the electrical configuration of a shared breaker between A & C or B & C condensate Pumps
- Provide suction flow to the Main Feed Pump, but can be used to supply water directly to the S/G’s in EOP-6 (Total Loss of Feed Water)
- Condensate Pumps each have bearing oil coolers cooled by turbine cooling water.
- Controlled by RTGB switches: Indicate pump breaker status, pump suction, & discharge valve. [Unit 2 has recirc valve position as well]
- Second Pump Started at 40% Power (~ 315 MWe)
If a single condensate pump is running, and trips due to an electrical overload or fault, the other Condensate Pump will auto-start
Unit 1
10,200 gpm
Normally supplied from Condensate Pump discharge header via Regulator PCV-12-50}. Need to line up the alternate seal supply from the Condensate Transfer Pump for the first Pump start.
Trips on MSIS
Prevents the condensate pumps from feeding a S/G fault if the MFIV should fail to close on a MSIS.
Electrical – overload, fault, undervoltage
Unit 2
9400 gpm
Pumps are self-sealing once they are running]. Need to line up the alternate supply from the Condensate Transfer Pump prior to each pump start
Trips on Electrical – overload, fault, undervoltage
Discuss ‘C’ Condensate Pump Transfer Switch.
a) Obtain keys from the control room. Unit 1 needs one key because one is captured. Unit 2 needs two keys as neither are captured.
b) Ensure both pumps are off and rack out applicable breaker. Inserting and turning a transfer key before the breaker is racked out will automatically trip the running pump
c) Ensure trip fuses remain in the racked out breaker cubicle. This allows the “OK to Transfer” light to energize and the Solenoid Key release).
d) Insert lower key and unlock - verify “OK to Transfer” light is lit, relock and remove key. “OK to Transfer” light should remain on.
e) Insert both keys into the upper slots and unlock. This allows rotation of the transfer switch to “C” (or “A”, “B”) positions.
f) Relock & remove upper key[s] for pump removed from service {other key is captured on Unit 1 only}
g) Rack in the appropriate breaker and verify Breaker Amber Lights and RTGB amber lights indicate power to the correct pump is aligned and Start the pump as desired.
Discuss Condensate Pumps Minimum Flow Recirc Valves (AOV’s).
- Each condensate pump has a minimum flow recirculation line that assures sufficient flow through the pump for cooling.
- Each pump discharge line contains an air operated recirculation flow control valve (FCV-12-3A, B & C).
- The recirculation valves are normally closed during full power operations.
Unit 1
2,500 GPM
To avoid damage:
Do not operate > 2 hours if <5000 gpm.
- Recirc valve is locally controlled via an “OPEN/CLOSE” switch. Should be open <2500 GPM.
- “CLOSE”: Will close the valve under any condition.
- “OPEN”: Will auto open valve if condensate pump is running. Will auto close upon pump stop.
- Alarm if switch in OPEN, pump running for > 10 seconds, and < 2,000 gpm recirc
Alarm if switch in CLOSE or pump stops and valve doesn’t close in 10 seconds
Unit 2
3000 gpm for 2B
To avoid damage:
Do not operate > 2 hours if <3000 gpm.
- Recirc valve is locally controlled via an “OPEN/CLOSE” switch. Should be open <3000 gpm.
- “CLOSE”: Will close the valve as long as the pump’s discharge valve is at least partially open. (Can’t be closed, needs a discharge path)
- “OPEN”: Will open the valve under any condition.
Discuss Miscellaneous Condensate Loads.
- PCV 12-49: 75 psig supply of condensate to Vacuum Breakers loop seal, CST Loop Seal, Integral Tube sheet Head Tank, and Chem. Add Tank
- MFW pump seals – Pressure regulator @ the feed pump controls the supply pressure
- S/G cold fill
Discuss SG Fill Path.
- SG Fill Isolation valve: V09218 – Normally closed during power operations
- Supplied from just downstream of the condensate pump discharge valves and taps into the feed header in between the discharge of the 5th point heaters and the feedwater regulating valves.
- Used for:
a) Initial SG fills after outage & cleanup of condensate & feed system
b) Appendix X of EOP-99 requires cold fill isolation valve to be opened 15-20 turns to maintain FW header pressure following a Rx trip to prevent water hammer in hot FW Heater & piping.
c) Also opened in EOP-06, for re-establishing a heat sink following a total loss of feedwater should aux feed or main feedwater be unavailable. As the S/G’s are depressurized, Condensate flow should begin flowing into the S/G once pressure gets ~ < 600 psig
Discuss Steam Jet Air Ejectors.
- SJAE’s consist of two sets of nozzles (2 primary and 2 secondary) and share the same Intercondenser & Aftercondenser
- Primary jets draw a vacuum on the main condenser, and discharges to the intercondenser.
- The Secondary jets draw a vacuum on the intercondenser, and discharges it’s exhaust to the Aftercondenser
- Inter Condenser - Condenses steam from the first stage of SJAE. Condensate drains go to the Main Condenser. Steam discharge goes to the after condenser.
- After Condenser - Condenses steam from the second stage of SJAE. Condensate drains to Condensate Recovery Tank.
Steam discharge is directed to either the Plant Stack plant exhaust stack via a rad monitor and flow element (normal alignment) or to Atmosphere (alternate alignment).
Discuss Gland Steam Condenser.
- Collects Gland Seal leak off steam and condenses it
- Condensate drains back to Condensate Recovery Tank then goes to the MC
- Non-condensable gases are exhausted to atmosphere via the Gland Exhaust Fan. Manually positioned discharge dampers maintain condenser shell pressure at 14 – 18 inches of water. The Gland Exhaust Fan discharge combines with the SJAE discharge on the way to the plant stack.
- Flow orifice in the condensate header creates a D/P which forces adequate flow through the Gland Exhaust Condensers.
Discuss Condensate System Recirc Valve – FCV-12-1.
- Maintains flow thru SJAE and GS condensers during low condensate flow conditions
- Positioned automatically by Flow Transmitter (FT-12-1)
- Opens to maintain flow {> 8000 gpm} [>10,000 gpm]; CR alarm on low flow
- Fails closed on a loss of air to try and prevent MFP trip due to low suction pressure.
- Could cause a loss of MC vacuum when inadvertently closed by not allowing enough condensate flow through the SJAE & Gland exhaust condensers
- Both units are initially set to 1000 gpm for starting on a depressurized header
- Located on the Mezzanine deck NE corner of condenser
Discuss Exhaust Hood Spray Valves (2) – (TCV-22-61A & B).
- Prevents LP Turbine rotor overheating at low loads or low vacuum
- If 2/3 exhaust hood temperature probes on either exhaust hood reaches:
Auto opens spray valves @ 160F
Alarm @ 175F
Turbine trip at 250F
What is the purpose of Feedwater Heaters?
- To preheat the Feedwater before it gets to the SG to: Raises temperature ~ 50 F / Heater
a) Reduce Thermal Shock
b) Gain in Cycle Efficiency - Only Heater 5 is designated as High Pressure, tube side pressure (discharge side of MFPs)
- Normal and Alternate LCV’s maintain designed level in each heaters shell.
- FW heater shell sides have vent lines containing orifices to vent air & non-condensible gases. They are manually aligned to the condenser when the heater is in service. They originate from the center of the tube bundle.The drains exit each heater via a subcooled section which subcools the fluid to try and prevent flashing across the Normal LCV as it drains to the next lower pressure heater.
Discuss Feedwater Heater Operation.
- One or more non-series heaters in the same train can be removed from service
- Two heaters in series in same train can be removed from service if all #5 heaters are removed from service and load reduced by 5% for each heater out of service
- Heaters 1 & 2 are in the Main Condenser, must be Bypassed Together. Heaters # 3, 4, & 5 and the Drains Cooler each have an Individual Bypass
- Extraction Steam is the first fluid to be removed on S/D and last to be added on S/U
