Main Steam (SG) Flashcards
Besides the HP turbine, where else does the SG system send steam to?
MSRs
Feedwater Pump turbines
steam seal system for the main turbine and feedwater pump turbines
Aux Feed Pump A
AS system
How are the Steam Generator Downcomer feedwater Control Valves operated and how are they normally controlled?
Pneumatically operated and are normally controlled by the Digital Feedwater Control system
they can also be controlled by operator action in the Control Room
How are the Downcomer feedwater 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, below 15%
Concerning the main steam system, what is “Swapover”?
At ~15% power and increasing, Downcomer Control Valves throttle closed and the Economizer control valves throttle open, directing all flow through the economizer lines
Reactor power is ascending. In the SG system, after the downcomer control valves close and the economizer valves open, will it stay in this line-up?
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
Why are there two steam generator Feedwater Downcomer Isolation Valves? How are they operated?
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
IA and nitrogen to open, spring close
(can also open manually)
How are the steam generator Downcomer Isolation valves affected by a loss of IA and Nitrogen backup?
How do they fail on a loss of power?
The valves fail closed
fail open
How can I open the steam generator 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
Why is the steam generator Economizer line not used during low power operation?
Due to insufficient preheating of the feedwater
What happens to the S/G Economizer Control valves on a loss of power or air?
Fails locked (as-is)
What happens to the S/G Economizer Feedwater Isolation valves upon a loss of power? Where does power come from?
Fail closed
supplied directly off the battery or from the PK ‘A’ or ‘B’ bus
What signal would shut the S/G Economizer Feedwater Isolation Valves?
MSIS
Concerning the S/G Economizer Feedwater isolation valves, what happens when the FAST CLOSE pushbutton is depressed?
5000-5400# accumulators are lined up directly to the top of the cylinder to close the valves
Why does each steam outlet nozzle of the S/G have an integral flow orifice?
To limit steam flow in the event of a steam line break
Why are the MSSVs (main steam safety valves) designed to lift 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 the MSSVs (main steam safety valves) closed?
Spring force
When would I use the ADVs (atmospheric dump valves)?
Opened as necessary to remove heat from the RCS when the main Condenser or SBCS (steam bypass control system) is not available, such as when the MSIVs are closed
How are the ADVs (atmospheric dump valves) operated?
Air operated with Nitrogen backup
can be operated manually
What would cause the SG ADVs to fail closed?
Loss of power and loss of all pneumatic pressure
Where can power to the MSIVs (main steam isolation valve) 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?
Fail closed
What happens if air is lost to the MSIVs?
Designed to not change position and remain capable of Fast Closing
