CW- Circulating Water Flashcards
The CW system serves as a discharge point for what sources?
CD system overboarding, CD and blowdown demineralizers low TDS Sumps, yard area sump pumps and Essential Spray pond Backwash Sump Pumps, Turbine building run off
Can be used as an emergency fire water source
What does TB do for the CW system?
Supplies makeup water from the storage reservoirs to the CW system to replace water losses due to evaporation, blowdown, and drift from the cooling towers
Provides blowdown paths to the evaporation ponds to allow constant blowdown for chemistry control and for level control in the canal
Why are we worried about silica in the CW system?
Plates out on the surfaces of the titanium tubes in the condenser
What chemicals are added to the CW canals with the CI system?
Hypochlorite, foam control agent, sulfuric acid, and scale dispersant
Who normally maintains the CW canal chemistry?
Water Resources
How does PW interact with CW?
The PW pumps share the intake canal with the CW pumps, utilize the Cooling Towers for cooling, and return their discharge to the CW return piping
What system provides air to the Cooling Tower Makeup Anti Cavitation Air Injection to prevent valve chattering in the Canal Level Control valve? What else does this system do?
Instrument Air
operates control valves and controllers
What is the approximate evaporation rate of the CW system at each unit?
18,000 gpm
Approximately how much water is lost to blowdown at each CW canal?
~700 gpm
but up to 2000 gpm
What is provided at each CW pump bay to prevent large debris from entering CW system?
Trash screens
Why are each of the pump slots provided with a Stop Gate?
In the event that maintenance is required on individual pumps while the system continues to operate
What provides water for screen spraying?
PW pumps
Due to recent modifications, where are the Turbine Building Roof drains directed to?
Their respective CW intake canals
What is the normal level setpoint of the CW canal?
23 ft
How often are local grab samples performed on the canal and what are they used for?
Daily
Used to determine the required blowdown flowrate for control of the chemistry parameters
What is the capacity of each CW pump? What is the normal discharge pressure of each pump?
25% (140,000 gpm)
~45 psi
What provides cooling to the CW pump lube oil cooler?
Turbine Cooling Water
What needs to be met in order for the CW pump to start when the switch in the Control Room is taken to START-OPEN?
Pump discharge valve is fully closed
Either the same flow train condenser outlet valve is open or the CONDENSER OUTLET VALVE INTERLOCK OVERRIDE pushbutton is depressed
The pump-start signal is sent to what other components?
Open signal for the pump’s discharge valve
Permissive signals to the CI system acid injection pump, CI system chlorine injection valves, and the same flow train CW pump discharge valve
What happens when I take the CW pump which to STOP-CLOSE position?
A closing signal is sent to the pump’s discharge valve
When the valve closes to less than 8% open, the pump’s breaker will open, stopping the pump
A signal is also sent to the CW supply header cross-tie valve and to the other CW pump discharge valve control logics
How could I get the CW pumps to stop immediately?
Depress the Emergency trip pushbutton in the Control Room
Where are the local switches and emergency pushbuttons located for the CW pumps?
Provided at each switchgear
Why are the B and C Condenser tube lengths greater than those in A?
To compensate for the higher circulating water inlet temperature
How quickly are the motor operators of the CW pump discharge valves designed to open or close?
30 seconds
What is the interlock associated with the CW pump and its discharge valve?
Each discharge valve is interlocked with its respective pump to only be open to 44% whenever there is one pump operating in its train, and the supply header cross-tie valve is closed
How quickly are motor operators of the condenser isolation valves designed to open or close? Where are they located?
60 seconds
inlet and outlet of each side of the condenser
What is the interlock associated with Condenser outlet Isolation Valves? What are the interlocks for the inlet isolation valves?
Outlet valves will not open unless the “water box full” permissive is satisfied
Once the water boxes are full, the outlet valves can be opened and the head of the cooling tower will maintain the piping full prior to the CW pump start
-No interlocks for inlets
What is the purpose of the CW system automatic vent and vacuum breakers? Where are they located?
To maintain the CW system and waterboxes full of water during normal system operation by automatically releasing any air that may collect in the system, while maintaining the water in the system
at the high points on the inlet and outlet water boxes of each shell of the condenser, on the supply header cross-tie line on both sides of CWN-HV-11 and at each CW pump discharge.
What are the major sections of the CW towers?
Water supply riser, circumferential distribution flume, distribution basin, fill ring, collection basin, and fan deck and support columns
Why does Tower 2 have a PW return pipe?
So that it may be used for PW service if the CW system is not operating
How many Cooling Tower fans are there for each tower? What is their diameter?
16
10 meters
What protections are provided for the Cooling Tower fans? How are they controlled?
High vibration, bus undervoltage, and electrical protection trip
switches in the control room send signals through plant multiplexer
How many Screen Wash Sump Pumps are there? What is the purpose of the screen wash sump? What is the purpose of the flow orifices in the sump pump discharges?
Two
trash screen cleaning, CW pump seal leakage collection and overflow from CW pump bays
control pump run out during operation
When would the Standby Screen Wash Sump Pump auto start?
Hi-Hi level in sump
What are the power supplies of the CW pumps?
‘A’ and ‘B’ – NAN-S01
‘C’ and ‘D’ – NAN-S02
What impact on the system does a loss of CW makeup have?
The pumps ability to take suction
What would happen upon a loss of CW Blowdown?
Would cause the chemicals of the CW system to concentrate and drive the CW water chemistry out of spec which would increase corrosion
What would happen upon a loss of Turbine Cooling Water?
Will cause the CW pump motors to overheat and alarms would be received in the control room on high temperatures
Pumps could fail if no operator action is taken
What happens if CW is completely lost?
Will result in immediate plant shutdown due to high condenser pressure
Decay heat will be rejected to atmosphere through steam bypass valves 1007 and 1008
What happens on partial loss of CW?
Plant will have to be down powered depending on the severity of the loss of vacuum
What are the start permissives for the CW pumps?
pump discharge must be fully closed and same flow train condenser outlet valve is open
Why do the B and C sections of the condenser have longer tube bundles?
to compensate for the increased circulating water inlet temperature
Describe the timer for the motor operated discharge valves of the CW pumps.
When one pump is started, the respective discharge valve will open to 44%. If the second pump to start in the same flow loop is started, the respective discharge valve will open to 44%. The 3 minute timer will pass and the second pumps discharge valve will open to 100% and then the first pumps discharge valve will open to 100%.
If the second pump being started is in the opposing flow loop, both respective discharge valves will stay at 44%.
When would the CW supply cross-tie valve go closed? How long can the system operate with a single CW pump feeding both flow loops?
hand switch in auto and both pumps in one CW flow loop stop
no longer than 48 hours
During the fill and vent of the CW system, pressure is not sufficient to help seat the auto vents and they are manually isolated to prevent spilling water in the turbine building. When are the auto vents placed in service?
When enough CW pumps are running to ensure good seating
Which outlet vents on the main condenser vent lines have no isolation valve and just have relief valves?
1C and 2C
What is the flow path through the cooling towers?
up a concrete return pipe and into the distribution flume for radial distribution to the distribution basin through adjustable weirs. from the basin, the water flows down through holes in the basin floor to the fill ring. water flows through holes in the fill ring down through the fill media and into the collection basin and back to the canal
How do the cooling towers work to remove heat?
As the water falls through the rigorous path of the fill media, the latent heat of vaporization occurs. the cooling tower fans pull air through the fill media perpendicularly to the fall of the water droplets and as some of the water droplets evaporate, it removes the heat from the continuously falling water and air inside the tower
How long is the high-vibration trip disabled for during start up of the cooling tower fans? If there is a problem with the plant multiplexor, how are the fans started?
30 seconds
locally at the breakers
Why are the cooling tower fans started and stopped in a specific order? What changes about fan operation during winter months?
to equalize the loading of the fans and match the heat transfer requirements of the CW system
less fans are in operation to maintain condenser vacuum in spec
