Pressurizer Pressure Control Flashcards
How many Pressurizer heaters do we have?
120 heaters total
12.5 kw/heater for a total of 1500 kw
How are Pressurizer heaters divided up into groups?
- 108 backup heaters divided into 4 groups. Groups 1 & 3 have 24 heaters (300 kw/group), and Groups 2 & 4 have 30 heaters (375 kw/group).
- 12 proportional heaters divided into 2 groups of 6.
How are the backup heaters normally operated?
Normally in manual (always on).
What are the advantages if having the backup heaters in manual?
- Eliminates cycling
- Allows for better pressure control
- Gives quicker spray response
- Provides better boron mixing
How are the proportional heaters controlled?
Controlled by Pressurizer pressure controller.
At what Pressurizer pressure controller output signal are the proportional heaters on and off?
- Full on at 0% output
- Off at 33.3% output
What is the Pressurizer low level cutout?
At 36% level in the Pressurizer, heater breakers trip to prevent the heaters from becoming uncovered, and CV-2003 closes to isolate letdown.
What is the function of the heater control selector switch?
Selects which Pressurizer level controller sends the low Pressurizer level cutout to heaters and CV-2003.
What are the switch positions for the heater control selector switch?
- A - only ‘A’ level controller sends signal
- B - only ‘B’ level controller sends signal
- A-B (normal) - both ‘A’ & ‘B’ send a signal. If either get a low level of 36%, it will send a signal to trip the heaters and close CV-2003.
How does a loss of Y-01 affect the Pressurizer pressure control system?
Causes a loss of protective function to trip heaters and close CV-2003 on 36% Pressurizer level.
What is the function of Pressurizer spray?
Uses continuous spray to reduce thermal shock of the spray nozzle and provides better mixing of boron in the Pressurizer. Spray flow comes from PCS cold legs, so it keeps Pressurizer boron concentration closer to PCS boron concentration, which prevents a reactivity event if an out-surge occurs.
Where does Pressurizer spray flow come from?
PCS cold legs loop 2A (C PCP), and loop 1B (B PCP)
How are the Pressurizer spray valves operated?
- Air to open, fail closed
- Controlled by the Pressurizer pressure controller
- Uses D/P between PCS and Pressurizer for motive force for spray flow
At what Pressurizer pressure controller output signal are the spray valves open and closed?
- Closed at 66.6% output signal
- Full open at 100% output signal
How does operating with only 1 PCP in each loop affect Pressurizer spray flow?
Maximum 40% total spray flow
How does operating with 1 spray valve isolated affect Pressurizer spray flow?
Maximum 70% total spray flow
How does operating with only 1 PCP in each loop and 1 spray valve isolated affect Pressurizer spray flow?
Maximum 30% total spray flow
Where does aux spray come from and when is it used?
- Aux spray is provided by the charging pumps
- Used when spray is required and no PCPs are operating to provide flow (startups, shutdowns, and when on natural circulation)
How does the aux spray valve fail on loss of air?
Closed
What is the function of the Pressurizer spray valve bypass?
Bypass around each spray valve that is throttled to provide 1 gpm of continuous flow around each valve
What are the power supplies for the Pressurizer pressure controllers?
PY-0105A from Y-10
PY-0105B from Y-20
What is the pressure range controlled by the Pressurizer pressure controllers?
2010-2100 psia
What are the modes of operation of the Pressurizer pressure controllers?
AUTO (normal) - uses a set point to automatically control pressure.
MANUAL - slide bar controls output signal to heaters and spray valves
What are the output signal bands on the Pressurizer pressure controllers for the heaters and spray valves?
0-33.3% - heaters
- 3%-66.7% - dead band
- 7%-100% - spray
What is the function of the Pressurizer pressure control selector switch?
Determines which pressure controller is controlling PCS pressure
What is the status of the Pressurizer pressure controller that isn’t in service?
Kept in manual with its output signal set at 50% to prevent controllers from “fighting” each other if they were both in auto, since the controlling setpoints could never be exactly the same.
What is the function of LTOP?
Provides overpressure protection with Tcold < 430 F
What are the modes of operation of the LTOP controller?
LTOP and SDC
How does the LTOP controller function when in LTOP mode?
Sets PORV setpoint based on Pressurizer pressure and Tcold. Alarm comes in when pressure is within 50 psia of the setpoint.
How does the LTOP controller function when in SDC mode?
- Fixed set point
- Trip (opens PORVs) at 310 psia
- Alarm comes in at 265 psia
What are the power supplies for the PORVs?
PRV-1042B - D11-1
PRV-1043B - D21-1
Where do the PORVs relieve to?
Quench Tank
How do the PORVs fail on a loss of power?
Closed
What causes the PORVs to auto open?
- When trip setpoint is reached (variable when in LTOP mode, 310 psia when in SDC mode)
- When in AUTO and Pressurizer pressure reaches 2235 psia (block valves are closed at power, so this has no effect)
When are the PORVs in service?
When Tcold is < 430 F. Isolated by the block valves when Tcold > 430 F.
What is required to “arm” the PORVs?
- LTOP key switch in ENABLE
- PORV block valves open
