Main Steam Flashcards
What components & systems does main steam provide steam to ?
-HP turbine
-MSRs
-MFWP Turbines
-Steam seal system for Main Turbine & FW Pump Turbines
-Aux. FW Pump Turbine
-Aux. Steam system
What does Main Steam provide during startup, shutdown& abnormal, or emergency operations?
Provides means of dissipating heat generated from Nuclear Steam Supply Systems(NSSS) to either condenser or atmosphere
What is provided for cooldown of SG when condenser isn’t available ?
ADVS are provided for when the condenser isn’t available
What happens to RCS, if SG loses ability to remove heat from RCS ? What happens if it’s an extended loss of SG ability to remove heat ?
-Result in High Pressure & Temperature in RCS, which could lead to reactor trip
-Extended loss could result in core damage due to inability to lose decay heat
What could happen on a loss of FW to the SG ?
Results in inability to cool RCS, which could lead to plant trip due to low SG Water levels or High Pressure
What does the Steam Bypass Control system control ?
Employs 8 Steam Bypass Control Valves to control heat removal from SG during normal & abnormal operations
What does the Steam Bypass Control System(SBCS) control during startup ?
SBCS controls Main Steam Pressure either automatically or manually by adjusting bypass valves as needed to maintain steam header pressure
What happens on a loss of SBCS during startup,post trip, or whenever it’s controlling steam pressure ?
Results in high steam pressure & if not corrected by ADVs,Turbine Load, or Reactor Power Cutback could result in reactor trip
What’re Nitrogen accumulators used for ?
-Used for backup supply to ADVS,Downcomer FWIV, & Downcomer FW Control valves,
-Used to SG for blanketing during shutdown
What happens on a extended loss of nitrogen ?
Won’t affect valve operation because of accumulator, but if accumulators runs out while supplying them valves could shut
N2 IS ONLY USED ON A LOSS OF IA
What’re the SG Downcomer Valve Upstream Block Valves used for ?
Provided for remote isolation of the Downcomer Control Valves
How are the Downcomer Block Valves operated? What is the normal position of them ?
-Motor operated operated by handswitch in Control Room
-Downcomer Block Valve are normally opened gate valves
What’re the FW Downcomer Control valves normally controlled by ? Where is another alternate way they can be controlled by ?
-Normally controlled automatically by Digital Feed water Control System
-Alternately can be controlled by operator in Control Room
What position do the Feedwater Downcomer Control Valves fail in on loss of air or power to solenoid ?
They fail in the as-is position, on loss of air or power to solenoid
What is the flow percentage passing through Feedwater Downcomer Control Valves during Low Power operation ?
100% of flow is passing through Downcomer Control Valves
Why during low power operation does 100% of Feedwater flow pass through Downcomer Control Valves ?
Supplied sufficient preheating for incoming feedwater at lower power
What percentage of power do the Feedwater Downcomer Control Valves throttle close ?
At 15% power & increasing, the Downcomer Control Valves will throttle close
When Downcomer Control valves are throttled closed at 15%, what valve is throttled OPEN at 15% power?
Economizer Control Valves are throttled open sending ALL FW through Economizer lines
What is it called when the Downcomer Control Valves are closed at 15% power, & the Economizer Control Valve is opened at 15% power ?
It’s called “Feedwater Swapover”
What happens to the Downcomer Control Valves at 50% power ?
-Downcomer Control Valves are throttled set position to supply 10% of feed flow
-Between 50%-100% power
What does throttling the Downcomer Control Valve to 10% when at 50% power provide for the system ?
Provides sub cooling for Recirc water& promotes increased Recirc ratio in S/G
How are the Downcomer Control Valve Bypass Valves operated? What position are they normally in ?
-Motor operated valves operated from control room & is normally closed
When & why are the Downcomer Control bypass valves used ?
Used in Mode 3 to control SG water level being supplied by
Non-Essential Aux FW Pump (AFN-P01
How does the Downcomer Control Valve Bypass Valves switch in the Control Room work ? What position does the valve in ?
-Three position switch is used to either jog the valve close or open
-Valve fails as-is on loss of power
What’re the events that the Downcomer FW Isolation Valves are supposed to close on ?
Isolated FW from SG in event of steam line break,FW line break, or LOCA
How fast are Downcomer FW Isolation Valves supposed to close following a MSIS? Why do they need to close this fast
Within 9.6 seconds to:
-Control Radiation release in case of LOCA
-Prevent Containment overpressure
-Prevent overcooling the primary system
How many Downcomer FW Isolation Valves are there ?
There are 2 valves in series on each Downcomer line one is ‘A’ Train & other is ‘B’ Train
What’re the Downcomer FWIVS normal position ? What’re they operated by ?
-Normally opened
-Operated by Pilot Solenoid valves to open, spring loaded to close
-Operated from control room
When you take the Downcomer FWIVS hand switch in the control room to “OPEN” what happens ?
-Instrument air supplied to overcome spring actuated valve
-Which will align high pressure nitrogen reduced down to 240psig
-240psig nitrogen goes to bottom of valve actuator will overcome spring force to open Downcomer FWIV
What happens when Downcomer FWIV hand switch is taken to “close” in control room or when it receives MSIS?
-Nitrogen is ported off & springs will rapidly close valve
What happens to Downcomer FWIV on a loss of power& IA or Nitrogen ? Can they be manually operated ?
-Loss of DC Control power, will fail open Downcomer FWIV
-Loss of IA or HP Nitrogen, valves will eventually fail closed
-Provided with manual operators
During normal operation of Downcomer FW Isolation Valve,what two systems are used in conjunction with each other to operate the valve ?
IA used with HP Nitrogen to operate Downcomer FWIV by overcoming spring force holding valves closed
What is the SGN-X02 Accumulator used for during a Loss of Offsite power which causes loss of Nitrogen ?
Dedicated backup source for HP Nitrogen to provide control & operating pressure to operate Downcomer FW Regulating & Isolation Valves
How does Downcomer FWIV support “N” Aux. Feed Pump ?
Supports its in it backup capability for safety related Aux FW Trains during LOOP by opening to provide N-train flow path
How long can the Accumulator supply nitrogen for ?
Sized for a minimum of 12hr supply
If you lose IA then you lose the ability to align HP nitrogen to the Downcomer FWIV to open. What is used as a backup to IA to be able align HP Nitrogen to Downcomer FWIV
Nitrogen from HP header will serves as a backup to the pneumatic control signal via check valve at 95psig
What’s the Economizer FW control valves used for ?
Control flow to SG in conjunction with Downcomer FW Control Valves & Digital FW Control system
What do the SG Economizer Line Stop Valves do?
Allows remote isolation of the Economizer FW Line
Where are the Economizer Stop Valves operated by? What’re they powered by?
They’re operated in the control room & powered by non-class MCC
What’re the Economizer Control Valves used for ?
They control FW to the Economizer section of SG
What happens in the Economizer section of the SG ?
Incoming water mixes with water already in cold leg half to preheat the incoming FW to saturation temp.
Why is the Economizer line not used during low power operation ?
Not used due to insufficient preheating of Feedwater
Where are the Economizer Control Valves controlled from ?
-Normally controlled by Digital FW Control System
-Can be manually controlled by operators in control room
When are the Economizer FW Isolation Valves supposed to isolate FW from the SG ?
In event of Steam Line Break, Feedwater Line Break, or LOCA
How fast are the Economizer FWIV supposed to close ? Why’re they supposed to close fast ?
Supposed to close in 9.6seconds to:
-Control radiation release in case LOCA
-Prevent Containment overpressure
-Prevent overcooling primary system
What Independent system operates the Economizer FWIV ?
Hydraulic Supply System
Where does the Hydraulic pump take suction from & discharge to for Economizer FWIV Hydraulic system ?
Takes suction from oil reservoir & discharges to both accumulators
How is accumulators pressure maintained in the Economizer FWIV Hydraulic system?
Automatically maintained by pressure based on Instrument Air Control Signal
What’re the accumulators pressurized with in the Economizer FWIV Hydraulic system?
-Pre-Pressurized Nitrogen to 3000-3400psig
-Hydraulic pump is used to pump oil from reservoir to accumulator to raise combined nitrogen/oil pressure to 5000-5400psig
-5000PSIG REMEMBER THIS NUMBER !!
What is the 4 way hydraulic valve used for in the Economizer FWIV Hydraulic system? How is operated ?
Instrument air aligns 4 way valve to allow hydraulic pressure to top or bottom of valve actuator to either close or open the FWIV
What is the one air reservoir used for in the Economizer FWIV Hydraulic system?
-Used as backup source of air to operate 4way hydraulic control valve on loss of IA
-This ensures Economizer FWIV can be closed following loss of offsite power
What position will the Economizer FWIV fail in ?
They fail as-is and still be capable of fast closing
Where are the Economizer FWIV solenoid operated air control valves powered from ? What happens on a loss of power to the solenoids ?
-Powered from PK’A’ & PK’B’
-Loss of power to solenoids Economizer FWIV will fail closed
What control hand switch’s are in control room to operate Economizer FWIVS ?
The following ways to operate valve from control room are:
-Slow Open
-Slow Close
-Fast Close
-Test/Exercise
What is the tech spec minimum for the Economizer FWIV Hydraulic system accumulators ?
5000psig
What will make accumulators pressure fluctuate in the Economizer FWIV Hydraulic system?
Temperature fluctuations throughout day & wind conditions will cause pressure fluctuations in accumulators
What must be done if Economizer FWIV Hydraulic system accumulator pressure is dropping close to 5000 psig limit ?
-Control Room sends AO to raise pressure by adjusting 1of2 pneumatic pressure regulators at the valve to operate hydraulic pump
-Pump operated to raise pressure in both accumulators
When are the Thermal relief valves supposed to open & close on the Economizer FWIV Hydraulic system Accumulators ? Why’re they permanently isolated ?
-Supposed to open at 5400psig & close at 250-350psig
-They’re isolated from use due to them not reseating properly & being unreliable
Instead of thermal relief valve what is preferred to be used to relief pressure in accumulator when it reaches 5400psig?
There is a FWIV Hydraulic Relief Bypass Valve that is throttled open to lower pressure in both accumulators
During slow open/ close operation of the Economizer FWIV how does the Economizer FWIV Hydraulic system operate ?
-Solenoid valves will operate to align 4 way hydraulic control valve to isolate the Accumulators
-Once accumulators are isolated hydraulic pump will pressurize appropriate side of actuator to either OPEN or CLOSE valve
How is a fast close signal generated for the Economizer FWIV?
-Fast close generated by hand switch in control room or MSIS
How does fast close operation of the valve Economizer FWIV work ?
-Solenoid air control valve will align 4 way hydraulic control valve
-4 way Hydraulic Control Valve will line up accumulators to top of valve actuator
Why’re the pre charged nitrogen accumulators used for the Economizer FWIV “Fast Close” operation ?
The Nitrogen Accumulators act as driving force for hydraulic oil to close valve within 9.6 seconds
What is the primary chamber in the SG?
-Bottom of SG
-RCS pressure boundary
-Directs RC flow through SG
What does the Stay Tube in primary chamber of the SG do ?
Stay tube separates primary chamber inlet & outlet plenums
How many inlet & outlet nozzles are there in the primary chamber ?
One inlet nozzle and two outlet nozzles
What does 10% design margin mean for the SG Tubes ?
Means 10% of tubes in SG could be plugged without affecting steam pressure on secondary side
What does secondary side shell form?
-Forms pressure boundary between SG secondary side
-Containment atmosphere & contains SG internals
What is the secondary side shell constructed of ?
-Lower & intermediate shell
-Transition Cone
-Steam Drum
-Head
What is the Lower & Intermediate shell surround ?
Surrounds SG evaporator & Economizer sections
What is the Secondary Shel Transition Cone surround?
-Transition come surrounds SG evaporator section
-provides changes in diameter from intermediate shell to steam drum
What is the Head ? What does it provide ?
-Head is the top of the SG
-Provides with two main steam outlet nozzles connected to each Main Steam line
What do the Main Steam Outlet Nozzles have to protect against steam line break ?
Includes integral flow orifice which limits steam flow in event of steam line break
What does the Downcomer Feedwater Ring do ?
Distributes FW entering SG from the Downcomer Feedwater nozzle
When FW entered feed ring & directed to top of Downcomer region what does it mix with ?
-Combines with moisture separated from steam-water mixture & drains to Downcomer annulus
Why is the feed ring distributing water all around Downcomer region important ?
Limits tube steam space by putting relatively cold water FW into Thot tube region of SG
Why is Feedwater added through feed ring during emergency conditions ?
Prevents thermally shocking the U-Tubes
What does the Economizer do ?
Increases SG efficiency by preheating incoming Feedwater before it enters evaporator section
What is the wrapper plate in the SG do ?
Divided SG Downcomer & evaporator sections
What’re the Moisture Separators in the SG used for ?
Moisture Separators remove water from steam-water mixture leaving SG Evaporator section
How do the Moisture Separators work ?
-Have spinner blades using centrifugal force to separate heavier water droplets from steam
What’re steam dryers used for in the SG ?
They’re above Moisture Separators for additional moisture removal before leaving SG
How do the Steam Dryers remove moisture from the steam ?
Sends steam through a tortuous path removes moisture
When the water drains from Steam Dryers where does it collect? What is the water called that is removed by the moisture separators & Steam Dryers ?
-Drains to moisture separator support plate where it joins with water removed from moisture separators & Downcomer Feedwater
-It’s called recirculating water
What is the steam quality when leaving the steam dryers in the SG ?
Quality of approx. 99.9% less than .1%moisture
What are the Main Steam Safety Valves(MSSVs) supposed to do ?
Limit secondary system pressure <110% of design pressure when passing 100% design steam flow
How many MSSVs does each main steam line have ?
There is 5 MSSVs to each main steam line
How is the MSSVs relieving capacity work ?
-Relief capacity is divided equally between main steam lines
-Sufficient to pass greater than 100% steam flow
How do the MSSVs open to prevent overcooling RCS ?
-Open sequentially to minimize number of valve opening during over pressure condition
-Also REDUCES chance of safety valve sticking open, overcooling the RCS
What’re the drain lines used for on the MSSVs ?
Provided to remove moisture from relief chambers & outlet safety valves
How are the MSSVs held closed ? How are the MSSIV opened ?
-Held close by spring force
-Pressure increases to valve setpoint, then leakage has pressure buildup in huddle chamber which will rapidly open valve
Why is it desirable for MSSVs to open rapidly ? How far does it open when setpoint is reached ?
-Minimizes seat damage
-valves opens to full open where lift stop contacts cover plate
What’re the pressure relief setpoint of the MSSV?
1st: 1250psig
2nd: 1290psig
Last 3: 1315psig
How many ADVs are on each Main Steam Line?
There is one ADV on each Main Steam Line
When are ADVs used ?
Used to remove heat from RCS when Main Condenser or SBCS isn’t available
What is normally source used to operated ADVs ? What is backup source to operate the ADVS ?
-ADVs are air operated
-Backup nitrogen from a nitrogen accumulator below each ADV
Where can the ADVs be operated from ?
-Can be operated from control room
-Manually operated at the valve
What is the ADV design basis capacity ?
Adequate nitrogen for operation of single ADV during:
-Natural Circulation cooldown event
-Station Blackout
When is the ADV Block Valve supposed to be used ?
-Block valve will isolate ADV & only used for maintnence purposes
-DON’T use block valve if ADV is stuck open will damage block valve
What happens to ADV on loss of power & loss of ALL pneumatic pressure?
- Valve will fail closed
What’re the of the ‘A’ Aux. Feed Pump steam supply valves supposed to do ?
Provides ‘A’ Aux Feed Pump with steam
When do the ‘A’ Aux. Steam Valves supposed to open?
-Aux. Feed water Actuation signal(AFAS)
-Hand switch
Which SG supplies the ‘A’ Aux Feed Supply Valves ?
Both SG supply the AFA Feed Pump Turbine
What kind of valves are used for the AFA Supply Valves ?
-Electrically operated 6” gate valve
-Electrically operated 1” globe valve that is used to bypass the gate valve
When AFA steam supply valves receive an open signal what happens ?
-Bypass valve will open first 30sec to provide steam to spin AFA pump -Turbine to gain speed to cause Governor oil pressure to increase
What does the Governor oil pressure cause ?
Causes Governor actuator controlled steam admission valve to start closing before main steam supply valves open
Why is it important for governor actuator controlled steam admission valve to start closing before main steam supply valves open ?
Prevents initial admission of full steam to turbine, prevent overspeed of AFA Feed Pump Turbine
What happens after the AFA feed pump steam supply valve bypass valve is opened for 30 seconds ?
6” gate valve opens to provide steam to bring turbine to full speed & provide FW to SGs
Do both sets of AFA Steam Supply Valves open on a AFAS ?
Yes both both sets of valves will open, regardless of which SG has low level
Where are the AFA Feed Pump Turbine steam supply valves powered from ?
Powered from PKA-M41
How do the AFA Feed Pump Turbine Supply Steam Valves close?
-No auto closure, valves must manually be closed from control room
-No 30 seconds delay, all steam supply valves will immediately close
Where can main steam supply valves be operated from besides from the Main Control Room ?
Can be operated from Remote Shutdown Panel by two position switch
What’re the Main Steam Isolation Valves used for ?
Used to automatically isolate each main steam line when a MSIS is generated
What generates a MSIS ?
-SG Pressure Low
-SG Level High
-Containment Pressure High
What does the MSIV hydraulic supply system for each MSIV ?
-One oil reservoir (Both Trains)
-One Hydraulic Pump(Both Train
-Two air reservoir tanks(one per train)
-Two Nitrogen/Oil Accumulators(One per Train)
-Solenoid operated air control valve for each train
-4 way hydraulic Control Valves for each train
What’re the MSIV bypass valves used for ?
-Warms up downstream piping of MSIV
-Pressure equalization across MSIV to allow them to be opened
-Emergency operations of Main Feed Pump after MSIS
How many MSIV Bypass Valves are there for each SG?
One for each SG
What will close the MSIV Bypass Valves?
-MSIS
-Loss of power will fail close
-Loss of air will fail close
What do the Steam Bypass Control Valves do ?
Promise removal of heat from RCS by provides flow path to Main Condenser or to atmosphere
When is the Steam Bypass Control Valves available ?
-During all modes of operation when RCS can produce steam in SG
-Mode 1-4
How many Steam Bypass Control Valves are there ? What is the capacity of them as a group ?
-8 steam bypass control valves
-Can pass 100% of steam from SG
How do the Steam Bypass Control Valves work during normal operation ?
-Operated in Remote Automatic Mode with SBCVs closed
How does the SBCVs work during abnormal operations ?
Load rejection from main generator will open valves to maintain RCS temperature
How do the SBCVs operated during plant startup,cooldowns, or other times ?
-SBCVs may be operated in Local Auto,or manual on master controller
-Manual on individual valve controllers
-Local manual with AO controlling valve to control heat balance of plant
Where are the SBCS operated from ?
Normally operated from control room
Where are the Downcomer,Hot,& Cold Leg Blowdown Isolation Valves operated from ?
-Normally operated from in Control Room
-Can be operated manually if necessary
When will the Combined Blowdown Line Containment Isolation Valves close?
Upon a MSIS, AFAS, & SIAS
Where are the Blowdown Isolation Valves operated from ?
Operated from control room
