Pressurizer Pressure & Level Control Flashcards
(8 cards)
Where does the pressurizer tap off the RCS?
Hot Leg 4
What is the normal operating level band of the pressurizer? (include unit difference)
- Program Level 25 to 60%
- From 557F to 585.4F (U1)
- From 557F to 589.2F (U2)
Describe the design basis of the pressurizer pressure control system
The pressurizer is designed to accommodate load changes of 5% per minute with automatic rod control, 10% per minute step change with auto rod control, or 50% per minute with auto rod control AND steam dumps.
The pressurizer master pressure controller receives inputs from two different channels controlled by a three-position switch that selects: “457/456, 455/456, or 455/458”. What are the different functions that these channels provide?
Channel 455 (normally selected) - channel 457 alternate:
- Provides actual pressure signal for the master controller u-PK-455A
- Controls BOTH spray valve controllers u-PK-455B/C
- Controls variable ‘C” heater output
- PORV u-PCV-455A at +100 psig error signal (2335)
- Actuates pressure deviation high alarm at +75 psig error signal (2310)
- Actuates low pressure alarm and energizes backup heaters at -25 psig error signal (2210)
Channel 456 (normally selected) - channel 458 alternate:
- Actuates PORV u-PCV-456 at 2335 psig
- Actuates high pressure alarm at 2310 psig
Describe the necessity of the interlock associated between the controlling pressurizer pressure control channels (455 & 456) and their alternates (457 & 458).
An interlock exists between channels 455 & 457, and between 456 & 458, such that their train-related PORV cannot be opened, and will close if open, if either channel measures RCS pressure below 2185 psig. This is to prevent an inadvertent depressurization of the RCS if the controlling channel fails high.
Describe the design basis of the pressurizer level control system
The pressurizer level control system maintains the pressurizer water volume to satisfy the following:
- Operating level will be low enough so that the insurge resulting from a step load reduction of 50% will not cause a high level (92%) Rx trip.
- Operating level will be low enough that a turbine trip from 100% will not result in flow through the pressurizer safeties.
- Operating level will be high enough so that a step increase of 10% will not uncover the heaters
- Operating level will be high enough so that the cooldown resulting from a trip will not empty the pressurizer.
The pressurizer master level controller receives inputs from two different channels by a three-position switch that selects: “459/461, 459/460, or 461/460”, which generate an error signal to drive FCV-121 further open or further closed. What are the different functions that these channels provide?
Channel 459 (normally selected) - channel 461 alternate:
- Provides actual level signal for the pressurizer master level controller
- Energizes backup (BUT NOT ‘C’) heaters and actuates deviation alarm at +5% above program
- Actuates level deviation alarm at -5% below program
- Actuates pressurizer low alarm at 17%
- Deenergizes all heaters at 17%
- Closes all orifice isolation valves at 17%
- Closes letdown isolation valve LCV-459 at 17%
Channel 460 (normally selected) - channel 461 alternate:
- Actuates high level alarm at 70%
- Actuates low level alarm at 17%
- Deenergizes all heaters at 17%
- Closes all orifice isolation valves at 17%
- Closes letdown isolation valve LCV-460 at 17%
The pressurizer master pressure controller and master level controller actuate common components in response to deviations from setpoint (e.g. heaters), if a condition exists where the two conflict, which controller takes precedent?
The pressurizer pressure and level control system is level dominant. Therefore, if a level deviation exists that would cause heaters to turn on (+5% level above program) that the pressure controller would otherwise turn off, the heaters will remain on until the level deviation is clear.
