Main Steam System Flashcards
From memory, draw and label a one line diagram of the Main Steam system showing system interfaces and the following major components:
- Main Steam Isolation Valves (MSIVs)
- Atmospheric Steam Dump Valves (ADVs)
- Turbine Bypass Valve (TBV)
- MSIV Bypass Valves
- Secondary Code Safety Valves
- Steam Generators
- Main Turbine interface
- Main Feed Pump Turbine interface
- Auxiliary Feed Pump Turbine interface
- Air Ejector and Hogger interface
- Moisture Separator Reheater interface
- Gland Seal Steam interface
- Steamline Radiation Monitors
- System Instrumentation that provides indication in the Control Room
in accordance with P&ID M-205 and M-207.
DRAW
What are the power supplies to the MSIVs?
CV-0510, E50A
- D-11-1
- SV-0507B, Vent
- SV-0505B, Supply
- D-21-1
- SV-0508, Vent
- SV-0513, Supply
CV-0501, E-50B
- D-11-1
- SV-0507A, Vent
- SV-0505A, Supply
- D-21-1
- SV-0514, Vent
- SV-0502, Supply
On loss of power, MSIVs loose control room indication and use of control switches
Where are the MSIV solenoid valve cabinets?
Turbine Building
- This cabinet houses solenoid vavles powered from D-11-1
D-Bus Cableway
- This cabinet houses solenoid valves powered from D-21-1
How do MSIV handswitches operate?
HS-0501A and HS-0510A
Either control switch will close both valves
Each switch controls 2 sets of 2 solenoid valves.
- D-11-1 (1 supply & 1 Vent) per MSIV
- D-21-1 (1 supply & 1 vent) per MSIV
- Supply valves in series
- Vent valves in parallel
Switch to Close
- Solenoids Energize
- Supplies close (unlatch)
- Vents open (unlatch)
- MSIV goes closed via spring and steam force
Switch to Open
- Solenoids Deenergize
- Allows Vents to be latched first, then Supplies
- Valve goes open
Handswitches are returned to OPEN after actuation/CLOSE to prevent damaging solenoid valves (constantly energized in CLOSE).
What are the power supplies to the MSIV bypass valves?
MCC-3
Fail as is on loss of power
What are the ADV power supplies?
D-11-1
- CV-0779 and CV-0781 solenoid valves
D-21-1
- CV-0780 and CV-0782 solenoid valves
Fail closed on loss of power. Air to open.
What is the turbine bypass valve (TBV) power supply?
Solenoid valves powered from D-11-1
Fails closed on loss of power. Air to open.
What automatically closes an MSIV?
SG Pressure <=500 (2 of 4)
CHP
Handswitch to Close
What allows MSIV closure block?
3 of 4 SG pressure switches at 512 to 548 psia.
Must monitor pressure indicators for light indicating a switch is allowing block.
PB Blocks one SG and give alarm that it is blocks. Another PB blocks other SG, no alarm so you have to hope it “took.”
Alarm clears at 512 psia.
Will reset at 548 psia on 2 of 4 in that SG
What is CV-0511, Turbine Bypass Valve, quick open?
HIC-0780A, Steam Dump Controller
Input of Tave from TYT-0100 or TYT-0200
Quick Open Signal
- 386 AST Turbine Trip
- Tave is ≥ 556.9°F, steam dump control relay (SDCR) energizes to fully open the TBV.
Tave is less than 556.9°F. the quick open signal goes away.
CV-0511 is interlocked to prevent opening and will close if there is less than 5 inches of vacuum in the main condenser
What is the ADV quick open feature?
HIC-0780A, Steam Dump Controller
Tave from TYT-0100 or TYT-0200
- With 386 AST Turbine Trip
and
- Tave is ≥ 556.9°F,
- SDCR energizes and closes contacts to align the quick open air supply solenoids to the ADV valve actuators to fully open ADVs.
Will stay full open until Tave is less than 556.9F
What is CV-0511, Turbine Bypass Valve, and the ADV modulate feature?
- 386X1 AST relay arms Steam Dump Controller HIC-0780A.
- Modulating signal developed based on difference between HIC-0780A internally set Tref of 532F and Tave.
- The control system will modulate the ADVs and TBV from full open when Tave is at 556.9°F (25°F error) to full closed at 535°F (3°F error).
- For increasing Tave , the control system will modulate the ADVs and TBV from full closed when Tave is at 540°F (8°F error) to full open at 556.9°F (25°F error).F
From 535F to 540F, PIC-0511 controls Tave based on Steam Header Pressure
How and when does PIC-0511 control the TBV?
Tave 535 to 540F
- PIC-0511 controls based on steam header pressure from PT-0510.
- Setpoint on Controller in Auto is 900 psia (Psat for Tave of 532F)
- CV-0511 full open at 905 psia, 532.6°F.
- CV-0511 full closed at 895 psia, 531.3F.
- TBV pressure control function DOES NOT require a turbine trip
What is the TBV Auctioneer Circuit?
PM-0511 auctioneers the signals from PIC-0511 and HIC-0780A, taking the larger of the two signals.
The larger signal is sent to CV-0511.
If Tave is greater than 540F, the TBV should already be open based on PIC-0511 signal.
Even without PIC-0511 signal (MSIVs closed), CV-0511 will still modulate with ADV, HIC-0780A output.
CV-0511 is interlocked to prevent opening and will close if there is less than 5 inches of vacuum in the main condenser.
When does CV-0511, Turbine Bypass Valve, auto close?
CV-0511 is interlocked to prevent opening and will close if there is less than 5 inches of vacuum in the main condenser.
Why do the MSIVs close?
The MSIVs automatically close during a low S/G pressure condition of 500 psia or Containment High Pressure condition (CHP) of 4 psig to prevent a rapid uncontrolled cool down of the Primary Coolant System in the event of a main steam line break.
What function do the MSIV position switches provide?
The position switches for the MSIVs initiate a turbine trip signal if the valves are not fully open.
MSIVs closing (Not full open) with the plant at power also results in a reactor trip if power is > 15%
What is the purpose for automatically tripping the Turbine on the “MSIVs Not Full Open” condition?
To protect the MSIVs from damage (refer to DBD-1.09 section 3.2.11.3).
When and how do you block the Turbine Trip for MSIV not fully open?
Two key-operated ENABLE/DEFEAT switches are provided on C-01 to allow defeating the MSIV closure turbine trip.
Done any time you wish to have the MSIVs closed and the turbine latched.
Special tests - RPS tests requiring the turbine to be latched - Anything requiring the 386 AST relay to be latched (or other turbine trip relays) or when testing the turbine during a REFOUT
What happens during an unexpected rise in steam demand?
Rise in steam flow results in reactivity addition and reactor power levels are exceeded. Plant shutdown or Reactor trip may/will be required.
- PCS can be overcooled
- Potential for Safety Injection
- Potential Loss of subcooling
- Exceed PCS cooldown limits
- Set up for potential Pressurized Thermal Shock (PTS)
MSIVs close on LO S/G Pressure or are closed by Operator during EOP 1.0 actions.
- Closing MSIVs may or may not terminate the event.
- Asymmetric cooling in PCS continues as long as one S/G is blowing down and one is not
- Causes unusual temperature indications in the PCS until the event is terminated (S/G blows down).
What happens if E-50A is faulted/blows down?
The source of steam is lost to the P-8B Auxiliary Feed Pump once the S/G Blows dry.
What happens on an extended loss of instrument air?
Instrument Air supplies the motive force for operating the MSIVs, ADVs, and TBV.
During an extended loss of instrument air the ADVs are available due to the nitrogen backup feature. The MSIVs and TBV will not be available. The TBV does have an accumulator that would allow for a quick open signal, but no modulation.
What are RIA-2323 and RIA-2324?
RIA-2323 (RE‑2323) monitors in the “B” steam generator main steam lines
RIA‑2324 (RE-2324) monitors the “A” steam generator main steam line.
They are located between ADV taps and the MSIVs (7’ & 20’ downstream of the ADVs).therefore, monitors would not ‘see’ activity if flow was through ADVs alone.
High Steamline Radiation: Mitigation of the event would require a plant shutdown and cooldown, repair of leak (probably SG tube leak), and cleanup of the secondary systems.
What happens with a turbine trip with valve malfunction/controller failure for ADV/TBV?
Depending on what has failed, S/G pressures rise to S/G Code Safety setpoints.
If the TBV has failed, the ADVs can control temperatures low enough to prevent or minimize S/G Code Safety opening.
Higher S/G pressures and temperatures result in higher PCS temperatures
- PCS pressure control system responds to maintain pressure at setpoint, therefore subcooled margin is lowered.
The possibility of a S/G Code Safety sticking open is raised.
- Excess steam demand event