SG- Main Steam 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
When is the Main Steam system required to be available? When is the SBCS available?
Modes 1-4, and in Mode 5 under certain conditions
modes 1-4
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
Where are the steam generator 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 steam generator Downcomer Control Bypass valves fail upon a loss of air or power?
As-is
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?
The valves fail closed
When would the steam generator Downcomer Isolation Valves fail open? When would they close automatically?
Upon a loss of DC power
steam line break, feedwater line break, LOCA
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
If I lost IA, how long could the steam generator Downcomer Isolation Valves operate with the Nitrogen accumulator backup supply? Where is the nitrogen accumulator and all N2 valves located? What pressure is nitrogen regulated down to?
12 hours
140’ turbine building
240 psig
Where are the steam generator downcomer isolation 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 steam generator Economizer line not used during low power operation?
Due to insufficient preheating of the feedwater
How are the S/G Economizer control valves normally controlled?
By the Digital Feedwater Control system
What happens to the S/G Economizer Control valves on a loss of power or air?
Fails locked (as-is)
Where are the S/G Economizer control valves located?
120’ Mezzanine
What is the purpose of the S/G Economizer Feedwater Isolation Valves?
To allow remote isolation of the economizer feedwater line on the outside of the containment in the case of a steam or feed line break or LOCA
What is the difference between the two S/G Economizer Feedwater Isolation valves in each line?
Upstream is “A” train, downstream is “B” train
Where are the S/G Economizer Feedwater Isolation valves located?
120’ MSSS building
What happens to the S/G Economizer Feedwater Isolation valves upon a loss of power? Where does power come from?
Fail closed
supplied from the PK ‘A’ or ‘B’ bus
What happens to the S/G Economizer Feedwater 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 S/G Economizer Feedwater Isolation Valves?
MSIS
Concerning the S/G Economizer Feedwater Isolation Valves, when would the Accumulator Charge Test position be selected?
To verify proper Nitrogen pre-charge in the accumulator
Hydraulic pressure must be removed to perform this test
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
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 steam 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 we use the S/G downcomer feed ring to add feedwater? What does the downcomer feedwater supply mix with?
To prevent thermally shocking the U-tubes
moisture from moisture separators
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 S/G 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
In the S/G’s, what is the quality of the steam when it leaves the Steam Dryers?
~99.9%
Where are the MSSVs (main steam safety valves) located?
135’ MSSS, upstream of the MSIVs (main steam isolation valves)
(each one has a drain line to prevent accumulation in the relief chamber and on the valve)
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
Where are the ADVs (atmospheric dump valves) located?
150’ MSSS
The nitrogen backup for each ADV (atmospheric dump valves) should be able to provide ADV operation for what amount of time?
16 hours during a station blackout
What would cause the SG ADVs to fail closed?
Loss of power and loss of all pneumatic pressure
What is the purpose of the ‘A’ AFP Steam supply valves? Where are they located?
To provide the AFA feed pump turbine with steam when called upon by an AFAS or hand switch actuation
120’ MSSS
Concerning the ‘A’ AFP, when an AFAS 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-D21
alternate is output from same train battery charger
Where are the MSIVs (main steam isolation valve) located?
140’ MSSS
The MSIVs (main steam isolation valve)accumulators are charged to what pressure?
5000-5400 psig
5k is tech spec limit
What ensures that the MSIVs (main steam isolation valve) can be closed following a loss of offsite power and IA?
Two air reservoirs
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
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 Main Feed Pump after an MSIS
How are the MSIV Steam Bypasses effected by a loss of air, power or a MSIS? How are they operated normally? Can they be operated manually?
Fail closed
two Class solenoids for air open, spring close
yes
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? How are their actuators operated?
Six go to the main condenser, two go to atmosphere
IA for control and operating air
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 is the main purpose of the Main steam system?
deliver steam from the steam generators to the high pressure turbine, dissipating heat from the RCS to the main condenser or the atmosphere
In which plant mode does the RCS not rely on the steam generators for heat removal?
Shutdown Cooling
What happens on a loss of the ability of the steam generators to remove heat from the RCS by steaming?
high RCS temperature and pressure
trips the reactor
What happens in the Steam generators on a loss of feedwater?
plant will trip on S/G low water level or high pressure
What happens on a loss of the Steam Bypass Control System when it is controlling system pressure?
high steam pressure
if uncorrected, will cause plant to trip and/or high primary system temps and pressures
How does IA interface with the SG system?
provides operating air and/or control air to the:
All FWIVs, MSIV, MSIV bypass
economizer and downcomer feedwater control valves
ADVs
steam bypass control valves
What purpose does Nitrogen serve in the SG system? Is the loss of this system felt immediately?
fills ADV, downcomer FWIV, economizer FWIV, and MSIV accumulators
backup for downcomer feedwater control valve ops
N2 blanket in the S/G during shutdown conditions
No
Not in an emergency situation, when can the AF (auxiliary feedwater) system supply feedwater to either steam generator?
shutdown and low power conditions
typically with the non-essential pump
In how many seconds are the economizer and downcomer FWIVs designed to close?
9.6 seconds
What are the modes in which the economizer FWIVs and MSIVs can be opened and closed?
slow open
slow close
fast close
test/exercise
What is the main difference between the MSIVs and FWIVs?
MSIVs have one valve with two redundant class trains of accumulators
FWIVs are two redundant valves with their own class train accumulators
What is the purpose of the primary chamber in the steam generators?
forms part of the RCS boundary and helps direct RCS flow from the hot let, through the inlet plenum, through the tubes and into the outlet plenum and out the outlet nozzles to the cold legs
In the steam generator, what is the purpose of the lower and intermediate shells? Steam drum?
surround the evaporator and economizer
surrounds the moisture separator and steam dryer
What is the purpose of the economizer section of the steam generators?
increases steam generator efficiency by preheating incoming feedwater before it enters the evaporator section.
Is there a procedure for increasing or decreasing FWIV or MSIV accumulator pressure?
no, its “skill of the craft”
What is the purpose of the S/G downcomer hot and cold leg blowdown isolation valves? How are they operated? Location?
allows control room to select S/G blowdown flow source or to isolate blowdown all together
motor operated or manually, no auto features
in containment
What is the purpose of the S/G combined blowdown line containment isolation valves? How are they operated? Location? When would they fail closed?
isolates S/G blowdown manually or on a MSIS, AFAS or SIAS
air operated or manually
inside and outside containment (outside valves on the 100’ MSSS)
loss of power or air
What are the steam generator economizer line stop valves for? Powered from where?
remote isolation of the economizer feedwater line
NH
Which valves in the Feedwater lines to the S/Gs and the main steam lines from the S/Gs are spring forced closed?
ADVs, DC FWIVs, MSIV bypass
