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
If loss of ADV/TBV and issues with code safeties, then S/G heat removal is seriously impacted, the following will result:
S/G temperatures and pressures rise
- If the S/G Code Safeties do not maintain S/G pressures per design, the PCS temperatures rise.
- PCS temperatures rising may exceed the capability of the PCS Pressure control system to maintain PCS pressure.
- PCS pressures rise to PZR Code Safety setpoint
- If PZR Code Safeties lift to relieve pressure and heat removal via the S/Gs is not regained, PCS pressures will stay high limiting inventory make up to the PCS to the Charging Pumps (Above HPSI injection head).
- Core uncovery could occur
What is the design and functionality of ADVs, including load.
Four 8 inch, automatically actuated, atmospheric steam dump valves (ADVs) have a total capacity of 30% steam flow.
- Each valve is rated at 841,875 lbm/hr (7.5% of total steam flow)
The capacity of the ADVs is adequate to prevent lifting of the main steam safety valves following a turbine and reactor trip.
What is the motive force for the ADVs?
Air is supplied by Instrument Air with an air accumulator installed.
In addition to an air accumulator, there is N2 backup to the ADV air supply from the bulk N2 storage tank.
- Nitrogen pressure is regulated just below the set pressure of the normal air supply regulator (it is a “backup”).
- N2 is automatically provided as the normal air supply pressure lowers
Describe the design of the TBV, including load.
6 inch, air operated, automatically actuated turbine bypass valve (TBV) has a capacity of approximately 4.5% of rated steam flow (508,000 lbm/hr).
What are the ADV control room indications?
Red (open) and green (closed) position indicating lamp located on C-01.
All lamps will be out when the CVs are in some midposition.
What is, where is and what powers Steam Dump Controllers?
Steam Dump Controllers
ADV controllers are powered from Y-10
HIC-0780A, Steam Dump Controller located on Control Room Panel C-01
Sends a signal to ADVs and the Turbine Bypass Valve
- HIC-0780B, Steam Gen E-50B Atmospheric Dump Control and 0781B, Steam Gen E-50A Atmospheric Dump Control on C-33
- Must be in Auto to pass signal to valves
Operation
- Auto - Uses internally generated set point from computer. Requires turbine trip and modulates valves open per program.
- Manual – Operator must use slide bar to change signal output. Quick open is still available.
- Cascade - Rendered inoperable, no function
Indications
- Blue pointer indicates the internally calculated program value (0-100%)
- Red pointer indicates PCS selected Tave (515-615°F)..
- Yellow Alarm light in solid indicates an input out of range high or low.
- Yellow light flashing indicates a low voltage condition in the controller battery.
- Red light indicates a controller computer failure
What are the TBV controls, indications and their power supplies?
Red and Green position indicating lights on C-01
- Green until 25% output signal, then Green and Red lit
- Green goes out at full open
PIC-0511 Turbine Bypass Valve Controller
- Powered from Y-01
- Signal from PT-0510
- Does not open and will close if less than 5 inches vacuum.
- Controls at 900 psia setpoint (532F)
- Full open at +5 psia from setpoint (532.6F)
- Full closed at -5 psia from setpoint (531..3F)
Controller Indicating Lights
- Yellow light in solid indicates a process input/output failure or other internal problems.
- Yellow light flashing indicates a low voltage condition in the controller battery.
- Red light indicates a controller computer failure. Controller should fail to last good value but may not be held for long. Manual control may be available.
What is PM-0511 and its power supply?
PM-0511 is TBV autioneer circuit
Powered from Y-01
Passes higher signal from HIC-0780A or PIC-0511
What happens to SV-0589A at 80 psig instrument air?
Solenoid valve SV-0589A auto closes to isolate the air supply if instrument air pressure lowers to 80 psig. The TBV will fail closed.
S/G Pressure Indicators are where?
C-12
- PIC-0751A/B/C/D – A S/G
- PIC-0752A/B/C/D – B S/G
- 0-1200 psia
- Associated with S/G Lo Steam Pressure Reactor Trip and Lo S/G Main Steam Isolation Signal (MSIS)
What and where is S/G Pressure Indicator PI-0580?
C-01 Panel
0-1200 psia
What alarms, indication and controls are on C-33?
Atmospheric Steam Dump Controllers HIC-0780B and HIC-0781B
Must be in auto to pass signal from HIC-0780A in control room
What alarms, indications and control are on C-150 panel?
Auxiliary Hot Shutdown Panel C-150A
Steam Generator Pressure Indicators PI-0751E and PI-0752E.
0-1200 psia
HS-0102C routes Loop 1 Thot TE-0112HA and Loop 1 Tcold TE-0112CA from TYT-100 to the C-150A indicators if the AVG TEMP DISPLAY SELECT switch in the Control Room is in the ‘Loop 1’ position.
Selecting the C150A position on HS-0102C when TAVE Selector is in Loop 1 position (TYT-0100 in-service) is to be avoided.
- Opens the circuit between the TH input to the TYT-100 Computer and routes the TH signal to the C-150A panel.
- Seen as a high TH input by TYT-100 (uses a value of 600O F) to calculate TAVE. Therefore a TAVE signal is calculated to be > 557O F which is received by the ADV Controller
Controls and indication on C-01?
MSIV CV-0501 and CV-0510 Control Switches
- White, Green, and Red indicating lamps.
Turbine Trip When Not Fully Open Defeat/Enable Key Switches
Bypass Of MSIV Closure On Low SG Press Pushbuttons
MSIV Bypass Valve MO-0501 and MO-0510 Control Switches
- Green, Blue, and Red indicating lamps.
Atmospheric Steam Dump Controller HIC-0780A
- Atmospheric Steam Dump Valves Green and Red indicating lamps.
Turbine Bypass Valve Controller PIC-0511
- Turbine Bypass Valve Green and Red indicating lamps.
Main Steam Press indicator PI-0580
- 0 to 1200 psia.
During startup of the main steam system, what is the status of the steam traps?
Bypassed for 2-hours with steam pressure greater than 50 psig.
Warms the lines and removes condensate that could damage turbines.
What is hot zero power steam pressure?
What is hot full power steam pressure?
Hot zero power: 900 psia
Hot full power: 770 psia
Why does the SDCR require an 8 degree error signal before modulating open?
At 8 degrees from zero load refeerence temperature (532F) the control begins modulating the ADVs open. An 8 degree erros signal keeps the vavles from accidently opening, hunting or short cycling.
If the SDCR has the ADVs at 75% open, what is Tave?
8 degree error represents full closed.
25 degree error represents full open.
17 degree span.
75% of 17 is 12.75 degrees.
Tave is 532 + 12.75 or 544.75 F
