[SG] - Main Steam Flashcards
Where does [SG] send steam to besides HP turbine?
(5)
-MSR’s
-Main Feedwater Pump turbines
-steam seal system for the main turbine and feedwater pump turbines
-[AF] Pump A
-[AS]
How are the [SG] Downcomer Feedwater Control Valves operated? How are they normally controlled?
Pneumatically - AOVs
Digital Feedwater Control system
(And also by operator action in the CR)
How are [SG] Downcomer Feedwater Control valves affected by a loss of air or power?
Fails locked (as-is) for both
At what point will the [SG] Downcomer provide 100% feed flow to the steam generators?
Low power operation (<15%)
[SG] What is “Swapover”?
At ~15% power and increasing, Downcomer Control Valves throttle closed
&
Economizer control valves throttle open, directing all flow thru 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 [SG] Downcomer Control Valves, Block/Bypass valves all located?
120’ Mezzanine
In Mode 3, what valve feeds S/Gs?
What is the mode of force?
-S/G Downcomer Control Bypass valves,
-non-essential AFP
How do [SG] Downcomer Control Bypass valves fail on a loss of air/power?
As-Is
Why are there 2 [SG] Feedwater Downcomer Isolation Valves?
How are they opened/closed?
2 safety trains
Open - [IA] / [N2]
Close - Spring
Note: also opened manually
How are the [SG] Downcomer Isolation valves affected by a loss of [IA]/[N2]?
Fail closed
When do [SG] Downcomer Isolation Valves fail open?
When do they auto close? (3)
-Loss of DC power
-steam line break,
feedwater line break,
LOCA
How do you open the [SG] Downcomer Isolation Valves after being shut by MSIS?
By placing the switch to CLOSE position (OVERRIDE light lit) then to the OPEN position
How long can the [SG] Downcomer Isolation Valves operate with the Nitrogen accumulator backup?
Where is the nitrogen accumulator and all N2 valves located?
What pressure is nitrogen regulated down to?
12 hours
TB 140’
240 psig
[MS] downcomer isolation valves location?
MSSS 100’
Where does the economizer line inject water into the S/G?
Why?
-Cold leg half of S/G
-preheats incoming feedwater to saturation temperature
Why is the S/Gs Economizer line not used during low power operation?
-insufficient preheating of feedwater
How are S/G Economizer control valves controlled normally?
-Digital Feedwater Control system
How do S/G Economizer Control valves fail on LOP/air?
-Locked (as-is)
Where are S/G Economizer control valves located?
120’ Mezzanine
What is the purpose of the S/G Economizer Feedwater Isolation Valves?
Allows remote isolation of economizer feedwater line outside of the containment in case of a steam/feed line break or LOCA
What is the difference between “A” & “B” S/G Economizer Feedwater Isolation valves?
“A” train is Upstream
“B” train is Downstream
Where are the S/G Economizer Feedwater Isolation valves located?
MSSS 120’
What happens to S/G Economizer Feedwater Isolation valves on a LOP? Where does essential power come from?
-Fails closed
-PK ‘A’ or ‘B’
What happens to the S/G Economizer Feedwater Isolation Valves on a loss of air?
-Do not change position and capable of fast closing
What ESF signal shuts S/G Economizer Feedwater Isolation Valves?
MSIS
When is the Accumulator Charge Test position selected for S/G Economizer Feedwater Isolation Valves?
To verify proper Nitrogen pre-charge in the accumulator
Note: Hydraulic pressure must be removed to perform this test
What happens when FAST CLOSE pushbutton is depressed on the S/G Economizer Feedwater isolation valves?
5000-5400# accumulators are lined up directly to the top of the cylinder to close the valves
How many U-Tubes in a S/G?
What percentage can be plugged without affecting steam pressure on the secondary side?
-12,580 tubes
-10%
What changes the S/G diameter from intermediate shell to steam drum?
-Transition Cone
What is the purpose of the integral flow orifice on the steam outlet nozzle?
Limits steam flow in a steam line break
Why is the S/G downcomer feed ring used to add Feedwater during emergency conditions?
What is mixed with the downcomer feedwater supply?
-Prevents thermally shocking the U-tubes
-moisture from moisture separators
What divides S/G downcomer and evaporator sections?
The Wrapper Plate
What design are the Moisture Separators in the S/G?
Cyclone
How do 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
What is the quality of the steam when leaving the S/G Steam Dryers?
~99.9%
Where are 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 do MSSVs (main steam safety valves) lift sequentially?
Minimize the # of valves required to open during an overpressure condition, which reduces the chance of a safety valve sticking open and overcooling RCS
What keeps MSSVs (main steam safety valves) closed?
Spring Force
When are ADVs used?
Opened to remove heat from RCS when the Main Condenser or SBCS (steam bypass control system) is not available, such as when the MSIVs are closed
How are ADVs operated?
Pneumatically w/ N2 backup
(Also operated manually)
(atmospheric dump valves)
Where are ADVs located?
MSSS 150’
N2 provides backup operation for ADVs for how long?
16 hours during SBO
What causes SG ADVs to fail closed?
LOP / pneumatic pressure
What is the purpose of the ‘A’ AFP Steam supply valves?
Where are they located?
Provides steam to AFA feed pump turbine on a AFAS/hand switch actuation
MSSS 120’
Why does the ‘A’ AFP bypass valve first open for 30 seconds on a AFAS?
Provides steam to spin AFA feed pump turbine to gain sufficient speed for the governor oil pressure to increase
Governor Oil pressure will cause the governor actuator-controlled steam admission valve to start closing before [MS] supply valves open preventing 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 MSIVs located?
MSSS 140’
What pressure are MSIVs charged to?
5000-5400 psig
T/S is 5000 psig
What ensures MSIVs can be closed on a LOOP and [IA]?
2 Air Reservoirs
Where can power to MSIVs come from?
‘A’ or ‘B’ Battery or PK ‘A’ or ‘B’ bus
What happens on a LOP power to MSIVs?
-Fail closed
What happens if air is lost to MSIVs?
Do not change position and capable of Fast Closing
What is the purpose of the MSIV Steam Bypass valves? (2)
Allow steam to be put into [MS] piping, independent of MSIVs to allow piping downstream of the MSIVs to warm for pressure equalization across the MSIVs, or to allow operation of the Main Feed Pump after an MSIS
How do MSIV Steam Bypasses fail on a loss of air/power/MSIS?
How are they operated normally?
Can they be operated manually?
-closed
-Opened w/ 2 Class air solenoids
Closed w/ spring
-yes
What is the purpose of the Steam Bypass control valves?
Remove heat from the RCS, via S/Gs by providing a flowpath to the Main Condensers or atmosphere for steam flow
How may Steam Bypass Control Valves are there?
Where are they located?
-8
TB 140’ (North & West of Main Condenser shells)
Where do the SBCVs direct steam discharge?
How are their actuators operated?
-6 go to main condenser
2 go to atmosphere
[IA] for control and operating air
What is meant by SBCVs “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 [MS] system?
Deliver steam from S/Gs to HP Turbine, & dissipating heat from RCS to the main condenser or atmosphere
When doesn’t the RCS rely on S/Gs for heat removal?
Shutdown Cooling
What happens when the S/Gs ability to remove heat from the RCS by steaming is lost?
high RCS temperature and pressure
trips the reactor
What happens to S/Gs on a loss of feedwater?
-Low water level/high pressure causing plant trip
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
[IA] interface in [SG]?
-air/control air to:
FWIVs, MSIV, & MSIV bypass
-economizer and downcomer feedwater control valves
-ADVs
-steam bypass control valves
[N2] interface in [SG]?
Is the loss of [N2] felt immediately?
fills ADV, downcomer FWIV, economizer FWIV, and MSIV accumulators
backup for downcomer feedwater control valve ops
N2 blankets S/G during shutdown conditions
No
When can the [AF] system supply feedwater to either S/G during normal operations?
shutdown and low power conditions
typically with the non-essential pump
How fast are the economizer & downcomer FWIVs designed to close?
9.6 sec
What modes can economizer FWIVs and MSIVs can be opened/closed?
-slow open/close
-fast close
-test/exercise
What is the main difference between the MSIVs and FWIVs?
MSIVs - 1 valve w/ 2 redundant class trains of accumulators
FWIVs - 2 redundant valves w/ own class train accumulators
What is the purpose of the primary chamber in S/Gs?
-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
What is the purpose of the S/G lower and intermediate shells?
Steam drum?
-surround evaporator and economizer
-surrounds moisture separator and steam dryer
What is the purpose of the economizer section of the S/G?
-increases S/G efficiency by preheating incoming feedwater before it enters the evaporator section.
Is there a procedure for increasing/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 CR to select blowdown flow source or isolate all together
-MOV or manually, no auto features
-CNTMT
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 is the purpose of S/G economizer line stop valves?
Where do they get Power?
-remote isolation of economizer feedwater line
-[NH]
Which valves are spring forced closed in the Feedwater lines to S/Gs and main steam lines from S/Gs? (3)
ADVs, DC FWIVs, MSIV bypass
What provides motive force to recirc water in the S/G during shutdown conditions?
Wet Layup Recirc Pump
