Main Steam (SG) Flashcards
Besides the HP turbines, where else does SG send steam to?
MSRs
Feedwater Pump turbines
Steam seal system for the main turbine and feedwater pump turbines
Aux Feed Pump A
AS system
When is the MS system required to be available?
Modes 1-4, and in Mode 5 under certain conditions
How are the Steam Generator Downcomer Control Valves operated and how are they normally controlled?
Pneumatically operated and are normally controlled by the Digital Feedwater Control system, although they can be controlled by operator action in the Control Room
How are the Downcomer Control valves affected by a loss of air or power?
Fails locked (as-is) on a loss of electrical power or air pressure
At one point, during reactor power operations, will the Downcomer provide 100% feed flow to the steam generators?
At low power operation
What is “Swapover”? Will it stay in this line up?
At ~15% power and increasing, Downcomer Control Valves throttle closed and the Economizer control valves throttle open, directing all flow through the economizer lines
No, at 50% power, the downcomer control valves start to re-open to supply 10% of all feed flow from 50% to 100%
This provides subcooling for the recirculating water and promotes an increased recirculation ratio in the S/G
Where are the Downcomer Control Valves, as well as the block and bypass valves, located?
120’ Mezzanine area
During Mode 3, what valve is used to feed the S/Gs and what provides the driving force?
S/G Downcomer Control Bypass valves, from the non-essential AFP
How do the Downcomer Control Bypass valves fail upon a loss of air or power?
As-is
When will the Downcomer Control bypass valves move?
When the control switch is held in the JOG OPEN or JOG CLOSED position
Why are there two Feedwater Downcomer Isolation Valves?
Upstream valve is “A” train and the downstream valves are “B” train, that way if one fails the other should operate to isolate that line
How are the Downcomer Isolation valves affected by a loss of IA and Nitrogen backup?
The calves will fail closed
When would the Downcomer Isolation Valves fail open?
Upon a loss of DC power
How can I open the Downcomer Isolation Valves after being shut by a MSIS?
By placing the switch in the CLOSE position and observing the white OVERRIDE light illuminated
The valve can be opened with the signal still present by taking the switch to the OPEN position
If I lost IA, how long could the Downcomer Isolation Valves operate with the Nitrogen accumulator backup supply?
8 hours
Where are these valves located?
100’ level of MSSS
Where is the water injected into the S/G by the Economizer line? Why?
Cold leg half of the Steam Generator to preheat the incoming feedwater to saturation temperature
Why is the Economizer line not used during low power operation?
Due to insufficient preheating of the feedwater
How are the Economizer control valves normally controlled?
By the Digital Feedwater Control system
What happens to the Economizer Control valves on a loss of power or air?
Fails locked (as-is)
Where are the Economizer control valves located?
120’ Mezzanine
What is the purpose of the Economizer Isolation Valves?
To allow remote isolation of the economizer feedwater line on the outside of the containment
What is the difference between the two Economizer Isolation valves in each line?
Upstream is “A” train, downstream is “B” train
Where are the Economizer Isolation valves located?
120’ MSSS building
What happens to the Economizer Isolation valves upon a loss of power?
FC
What happens to the Economizer Isolation Valves upon a loss of air?
The valves are designed to not change position and remain capable of fast closing
What signal would shut the Economizer Isolation Valves?
MSIS
Concerning the Economizer Isolation Valves, when would the Accumulator Charge Test position be selected?
To verify proper Nitrogen pre-charge in the accumulator
Hydraulic pressure mush be removed to perform this test
What happens when the FAST CLOSE pushbutton is depressed?
5000# accumulators are lined up directly to the top of the cylinder to close the valves
How many U-Tubes are in the S/G and how many can be plugged without affecting steam pressure on the secondary side?
12,580 tubes
10% of the tubes
What provides the changes in S/G diameter from the intermediate shell to the steam drum?
Transition cone
Why does each outlet nozzle of the S/G have an integral flow orifice?
To limit steam flow in the event of a steam line break
During emergency conditions, why would be use the feed ring to add feedwater?
To prevent thermally shocking the U-tubes
What divides the steam generator downcomer and evaporator sections?
The wrapper plate
What design are the Moisture Separators in the S/G?
Cyclone
How do the Moisture Separators operate?
Spinner blades are fixed, forcing the steam-water mixture into a circular motion
Centrifugal force separates the heavier water droplets from the steam
Water passes through holes in the side of the separator and falls to the top of the support plate
Where are the MSSVs located?
135’ MSSS, upstream of the MSIVs
Why are the MSSVs designed to life sequentially?
To minimize the number of valves required to open during an overpressure condition, which reduces the chance of a safety valve sticking open and overcooling the RCS
What keeps MSSVs closed?
Spring Force
What are the lift set points of the MSSVs?
1250, 1290, 1315, 1315, 1315 psig
When would I use the ADVs?
Opened as necessary to remove heat from the RCS when the main Condenser or SBCS is not available, such as when the MSIVs are closed
How are the ADVs operated?
Air operated with Nitrogen backup
Where are the ADVs located?
150’ MSSS
The nitrogen backup for each ADV should be able to provide ADV operation for what amount of time?
13.3 hours to allow reactor entry into shutdown cooling conditions
16 hours during a station blackout
What would cause the ADVs to fail closed?
Loss of power and loss of all pneumatic pressure
What is the purpose of the ‘A’ AFP Steam supply valves?
To provide the AFA feed pump turbine with steam when called upon by an AFAS or hand switch actuation
When a signal is received, why does the bypass valve first open for 30 seconds?
Provides steam to spin the AFA feed pump turbine and allows the turbine to gain sufficient speed to cause the governor oil pressure to increase
Governor Oil pressure causes the governor actuator-controlled steam admission valve to start closing before the main steam supply valves open
This will prevent an overspeed of the AFA feed pump turbine
What powers the AFA feed pump steam supply valves?
PKA-M41
Where are the MSIVs located?
140’ MSSS
Why do the two independent discs of the MSIVs rotate a few degrees during each closing stroke?
Equalizes wear on the seats and the discs
The MSIVs accumulators are charged to what pressure?
5000 - 5400 psig
What ensures that the MSIVs can be closed following a loss of offsite power and IA?
Two air reservoirs
Where can power to the MSIVs come from?
Supplied directly from ‘A’ or ‘B’ Battery or from the PK ‘A’ or ‘B’ bus
What happens if I lose power to the MSIVs?
FC
What happens if air is lost to the MSIVs?
Designed to not change position and remain capable of Fast Closing
What is the purpose of the MSIV Steam Bypass valves?
To allow steam to be put into the main steam piping, independent of the MSIV for the purposes of allowing warm up of piping downstream of the MSIVs, pressure equalization across the MSIVs, or to allow operation of the MFP after an MSIS
How are the MSIV Steam Bypasses affect by a loss of air or power?
FC
What is the purpose of the Steam Bypass control valves?
Provide the means to remove heat from the RCS, via S/Gs by providing a flowpath to the Main Condensers or to atmosphere for steam flow
How may Steam Bypass Control Valves are there and where are they located?
8, located 140’ Turbine Building, west and north of the Main Condenser shells
Where do the SBCVs direct their steam discharge?
Six go to the main condenser, two go to atmosphere
Concerning the SBCVs, what is meant by “disk stack”?
“labyrinth flow passages” etched into the flat surface of the disks, which make the flow past each disk a known amount, so throttling characteristics of the valve can be controlled
Made up of numerous disks stacked on each other and the total stack provides an operating chamber for the valve disk
What are your actions if the ADV are over 700 psig?
The control room cannot see pressure above 700 psig so we will have to go out and unisolate the pressure gauge and report back to the control room
What are the failed positions for isolation valves?
MSIV
- Power – closed
- Air – as is bc of reservoir
ADV
- Power – closed
- Air – closed
Economizer FWIV
- Power – closed
- Air – as-is because of reservoir
Downcomer FWIV
- Power – open
- Air – closed
