Digital EHC Flashcards
What is the purpose of Digital EHC?
Position Turbine Control valves, intercept valves, and bypass valves to achieve turbine load and to control reactor pressure during startup, shutdown, and cool down.
Achieve Turbine Speed and load consistent with the ability of the nuclear boiler to supply steam
What are the two inputs for DEHC Pressure Control?
Throttle Pressure and Dome Pressure
What is the primary (preferred) pressure control mode and why?
Dome Pressure due to smaller gain
What is the gain for Dome Pressure Control?
1.25%stm flow/1psi error = 100%stmflow/DomePressure(1000#) - Setpoint (920#)
What is the gain for Throttle Pressure COntrol?
3.33%stmflow/1psi error
What are the standard throttle and dome pressure at 100% steam flow?
950# throttle press, 920# dome press
What kind of control modules are used for DEHC control?
Tripple Modular redundant
Which value from the DEHC Triple Modular Redundant controllers is used?
Median value if all 3 are available
How many processors are in each controller and how many signals per processor
3 and 3
What are the two TMR Controllers and what is the third?
Turbine Controller (Q1), Pressure Controller (Q2), Protection Controller (P)
What are the three processors for the Turbine and Pressure COntrollers? For the Protection Controller?
R/S/T, R/S/T, X/Y/Z
What control does the the Turbine COntroller have?
All valves except Bypass. All Trips excep Backup Overspeed
What control does the Pressure Controller have?
Pressure Control Signal & Bypass Valve Controls
What protection does the Protection Controller Provide?
Backup Overspeed ONLY
How does the Dome Pressure Controller function?
Measures RPV pressure via 3 detectors, compares to setpoint, and develops error signal
What is the Max Combined Flow Limiter normal setpoint?
113.7% for U2, 114% for U3
What is the Max Combined Flow Limiter designed to do?
Designed to limit the max combined flow from both Control Valves and Bypass Valves to prevent damage to RPV.
How does the Throttle Pressure Control function?
Measures throttle header pressure via 3 detectors, compares to setpoint and develops error signal
What provides input to the Auto Tracking Function?
Both the Throttle and Pressure Control output
What happens if Dome Pressure exceeds Throttle Pressure by 200#?
Control will auto transfer to Throttle Pressure Control
What pressure difference will Dome Pressure Control auto transfer to Throttle Control?
Dome PRessure 200# greater than Throttle Pressure
Under what conditions would you expect Dome Pressure to exceed Throttle Pressure by 200#?
Rx isolated from Throttle Header
Dome Pressure transmitters fail High
What is the purpose of Dome/Throttle Pressure transfer when D exceeds T by 200#?
Prevents CV &BPV cycling when MSIVs closed
What is the DEHC Auto Tracking Function?
It constantly tracks error signal difference between active pressure controller and standby, and continuously adjusts standby controller demand to equal the one in service. THis ensures a BUMPLESS transfer
What does the Bypass Control Unit do?
Positions BPV based on demand from BPV jack control, Auto RPV C/D, summation of pressure demand and Turbine Control reference signal.
What happens if total steam flow demand exceeds turbine steam flow demand?
BPV control opens BPV sequentially to meet demand
What will happen to BPVs if Low vacuum condition is sensed and what is the “LOW” signal?
Positions them to min value, sensed at 7inHg, and bias to 0.
What is the purpose of the “Load Control Unit”
Designed to measure and compare turbine load vs demand settings
What is a PLU Runback and what does it do?
Actuates if a 40% mismatch occurs between generator stator amps and cross over header pressure. Sensed between HP&LP turbines (normal 215psi)
Initiates a Control Valve fast closure during load reject conditions.
Causes load set reference to runvack to a no-load condition of 2%
CV fast acting solenoids cause CV rapid close generating scram when EHC pressure drops.
How is Chest Warming Performed?
2 MSV internal bypass valve opens in first 1” of valve travel
What are the power supplies to DEHC?
Supplied by Instrument Bus and Computer UPS - auctioneered
Both supplies are always online supplying components in parallel.
GE UPS used on IB feed due to ABT momentary (6 cycle) loss of power
What interlocks are associated with DEHC?
Bypass Vavle steam demand low vacuum signal prevents opening bypass vlvs when condenser vacuum is below 7inHg
What happens with a PLU with Rx Power > 38.5%
Fast closure of CVs and IVs by actuating fast acting solenoid
When fast acting solenoid <590psig, scram signal sent to RPS
What happens to DEHC with loss of stator cooling?
Max load capability run to 25% within 2 minutes
IF Stator AMPS >27395 after 2 min, turbine trip
IF Stator AMPS >9121 after 3.5 min, turbine trip
IF RX Power >33.5%, SCRAM
What happens with a loss of ONE DEHC Pressure processor?
Still functions: Loss of B/U pressure regulation. COLR MCPR penalty
What happens with a loss of TWO Pressure Processors?
CV Closure due to loss of control signal, therefore no CV closure scram. Results in High Pressure or High Flux Scram
What happens with a Pressure Control Signal Fail Hi?
MCFL limits BPV demand to 13.7%
What happens on a failure of DEHC Pressure Transmitter?
1 failure - median of remaining will be used
2 failures - remaining signal will still be used - OPERATOR SHOULD CHOOSE OTHER MODE
What happens with a failure of the MCFL?
MCFL Fails Low:
BPVs will close down and CVs will close down causing Rx Flux, Rx Pressure and Throttle Pressure to rize
Eventual scram
What happens if the Pressure control signal fails low?
This is the same as the setpoint failing hi
- CVs and BPV close - resulting in Hi Flux or Hi Pressure Scram
Product of 2 processors lost or loss of all processors
- If in Dome controll and all throttle pressure sensors fail low, logic would auto swap to throggle and Rx scram would occur from High flux and high pressure.
