Digital EHC

Question 1

What is the purpose of Digital EHC?

Answer 1

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

Question 2

What are the two inputs for DEHC Pressure Control?

Answer 2

Throttle Pressure and Dome Pressure

Question 3

What is the primary (preferred) pressure control mode and why?

Answer 3

Dome Pressure due to smaller gain

Question 4

What is the gain for Dome Pressure Control?

Answer 4

1.25%stm flow/1psi error = 100%stmflow/DomePressure(1000#) - Setpoint (920#)

Question 5

What is the gain for Throttle Pressure COntrol?

Answer 5

3.33%stmflow/1psi error

Question 6

What are the standard throttle and dome pressure at 100% steam flow?

Answer 6

950# throttle press, 920# dome press

Question 7

What kind of control modules are used for DEHC control?

Answer 7

Tripple Modular redundant

Question 8

Which value from the DEHC Triple Modular Redundant controllers is used?

Answer 8

Median value if all 3 are available

Question 9

How many processors are in each controller and how many signals per processor

Answer 9

3 and 3

Question 10

What are the two TMR Controllers and what is the third?

Answer 10

Turbine Controller (Q1), Pressure Controller (Q2), Protection Controller (P)

Question 11

What are the three processors for the Turbine and Pressure COntrollers? For the Protection Controller?

Answer 11

R/S/T, R/S/T, X/Y/Z

Question 12

What control does the the Turbine COntroller have?

Answer 12

All valves except Bypass. All Trips excep Backup Overspeed

Question 13

What control does the Pressure Controller have?

Answer 13

Pressure Control Signal & Bypass Valve Controls

Question 14

What protection does the Protection Controller Provide?

Answer 14

Backup Overspeed ONLY

Question 15

How does the Dome Pressure Controller function?

Answer 15

Measures RPV pressure via 3 detectors, compares to setpoint, and develops error signal

Question 16

What is the Max Combined Flow Limiter normal setpoint?

Answer 16

113.7% for U2, 114% for U3

Question 17

What is the Max Combined Flow Limiter designed to do?

Answer 17

Designed to limit the max combined flow from both Control Valves and Bypass Valves to prevent damage to RPV.

Question 18

How does the Throttle Pressure Control function?

Answer 18

Measures throttle header pressure via 3 detectors, compares to setpoint and develops error signal

Question 19

What provides input to the Auto Tracking Function?

Answer 19

Both the Throttle and Pressure Control output

Question 20

What happens if Dome Pressure exceeds Throttle Pressure by 200#?

Answer 20

Control will auto transfer to Throttle Pressure Control

Question 21

What pressure difference will Dome Pressure Control auto transfer to Throttle Control?

Answer 21

Dome PRessure 200# greater than Throttle Pressure

Question 22

Under what conditions would you expect Dome Pressure to exceed Throttle Pressure by 200#?

Answer 22

Rx isolated from Throttle Header

Dome Pressure transmitters fail High

Question 23

What is the purpose of Dome/Throttle Pressure transfer when D exceeds T by 200#?

Answer 23

Prevents CV &BPV cycling when MSIVs closed

Question 24

What is the DEHC Auto Tracking Function?

Answer 24

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

Question 25

What does the Bypass Control Unit do?

Answer 25

Positions BPV based on demand from BPV jack control, Auto RPV C/D, summation of pressure demand and Turbine Control reference signal.

Question 26

What happens if total steam flow demand exceeds turbine steam flow demand?

Answer 26

BPV control opens BPV sequentially to meet demand

Question 27

What will happen to BPVs if Low vacuum condition is sensed and what is the "LOW" signal?

Answer 27

Positions them to min value, sensed at 7inHg, and bias to 0.

Question 28

What is the purpose of the "Load Control Unit"

Answer 28

Designed to measure and compare turbine load vs demand settings

Question 29

What is a PLU Runback and what does it do?

Answer 29

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.

Question 30

How is Chest Warming Performed?

Answer 30

#2 MSV internal bypass valve opens in first 1" of valve travel

Question 31

What are the power supplies to DEHC?

Answer 31

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

Question 32

What interlocks are associated with DEHC?

Answer 32

Bypass Vavle steam demand low vacuum signal prevents opening bypass vlvs when condenser vacuum is below 7inHg

Question 33

What happens with a PLU with Rx Power > 38.5%

Answer 33

Fast closure of CVs and IVs by actuating fast acting solenoid When fast acting solenoid <590psig, scram signal sent to RPS

Question 34

What happens to DEHC with loss of stator cooling?

Answer 34

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

Question 35

What happens with a loss of ONE DEHC Pressure processor?

Answer 35

Still functions: Loss of B/U pressure regulation. COLR MCPR penalty

Question 36

What happens with a loss of TWO Pressure Processors?

Answer 36

CV Closure due to loss of control signal, therefore no CV closure scram. Results in High Pressure or High Flux Scram

Question 37

What happens with a Pressure Control Signal Fail Hi?

Answer 37

MCFL limits BPV demand to 13.7%

Question 38

What happens on a failure of DEHC Pressure Transmitter?

Answer 38

1 failure - median of remaining will be used | 2 failures - remaining signal will still be used - OPERATOR SHOULD CHOOSE OTHER MODE

Question 39

What happens with a failure of the MCFL?

Answer 39

MCFL Fails Low: BPVs will close down and CVs will close down causing Rx Flux, Rx Pressure and Throttle Pressure to rize Eventual scram

Question 40

What happens if the Pressure control signal fails low?

Answer 40

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.