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ZZ LOIT CWS Systems 2018 > DFWC: Digital Feed Water Control > Flashcards

DFWC: Digital Feed Water Control Flashcards

1
Q

When will the DFWCS Master Controller enter and exit tracking on a Reactor Trip?

A

Exits at >51.9%NR SGWL

Enters at < 26%NR SGWL

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2
Q

If the 1E button on the DFWCS Screen is green and power is raised > 14% what will happen?

A

DFWCS will NOT automatically swap to 3E. One of the prerequisites to swap is that the 3E button is green (selected).

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3
Q

What is the Steam Flow deviation alarm setpoint in the DFWCS?

A

40%

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4
Q

When does DFWCS swap from 3E to 1E?

A

13.5% and decreasing

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5
Q

How does the Nuclear Instrumentation System interface with the DFWCS?

A

Provides Reactor Power Control Channels (UIC 1, UIC 2, or their average) to DFWCS so it can determine:

  1. When to use 1 Element Control or 3 Element Control
  2. Swapover Logic
  3. Total Feedwater Flow indication determination
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6
Q

What is the Feedwater Temperature deviation alarm setpoint in the DFWCS?

A

4%

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7
Q

From where do the Main Feed Pumps get their speed signal?

A

The DFWCS Master Controller

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8
Q

What does DFWCS do?

A

It controls feed flow to the SGs over the range of 2% to 100% automatically

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9
Q

Does each SG have its own control system?

A

Yes. DFWCS 1 for SG #1 and DFWCS 2 for SG #2

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10
Q

What causes an “ATUN Lockout”?

A

8% deviation between Reactor Power instruments or

8% deviation between Feedwater Temperature Typically a transmitter failure will be the cause of this.

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11
Q

At what power levels is the Downcomer Feed Flow used as the Total Feed Flow indication?

A

< 13%. It will automatically swap to actual Total Feed Flow when power > 13%.

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12
Q

What is the Reactor Power deviation alarm setpoint in the DFWCS?

A

4%

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13
Q

What is the DFWCS Master Controller output limited to when RTO is in effect? Why?

A
  • 9%

- Because the Master Controller is tracking the RTO Controller at this time and the RTO Controller is limited to 9%.

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14
Q

What is used to tune the proportional band and integration rate while DFWCS is in 3 Element Control?

A 
Feedwater Temperature
Reactor Power (Control Channels)
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15
Q

Describe the response of the DFWCS on a shutdown.

A

50% - Downcomer Control Valves close
15% - Swapover
13.5% - DFWCS shifts from 3E to 1E
13% - indicated feed flow changes from the Total Feed Flow transmitters to the Downcomer.

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16
Q

Does DFWCS 3 Element control utilize SBCS inputs?

A

No

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17
Q

What is High Level Override in the DFWCS?

A

When SG is too high (>88%NR), the DFWCS will close the Downcomer and Economizer Control Valves in an attempt to lower SGWL.

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18
Q

What limit is imposed on the DFWCS Master Controller when power is < 15%?

A

Max output is limited to 25%.

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19
Q

What results from an “ATUN Lockout”?

A

The use of canned values for tuning purposes.

  • 425F for Feedwater Temperature
  • Reactor Power:
    • 5% for Rx Power if < 16.5%
    • 60% for Rx Power if > 16.5%
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20
Q

In addition to SGWL, what else inputs into the DFWCS when in 1 Element Control?

A

SBCS demand and TLI from RRS.

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21
Q

On the way up, what are the requirements to perform Swapover?

A

Power > 16.5%
OR
Power between 15% and 16.5% with either Downcomer Control Valve > 80% open.

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22
Q

Which is faster: 1 Element or 3 Element?

A

3 Element

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23
Q

How do you clear an “ATUN Lockout”?

A

Place the failed transmitter in ‘maintenance’ and touch the red “ATUNE LKOUT” flag on the digital controller

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24
Q

What is Reactor Trip Override (RTO) in the DFWCS?

A

When the Reactor trips, SGWLs will lower rapidly due to shrink from the power reduction. RTO will feed the SGs much slower than the level deviation would normally call for.

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25
Q

What is the Total Feed Flow deviation alarm setpoint in the DFWCS?

A

4%

26
Q

What is the purpose of tracking in the DFWCS?

A

To provide a bumpless transfer when shifting from one mode of operation to another.

27
Q

If the normal power (NNN-D11) for DFWCS returns while its being powered from its alternate supply (NNN-D12) what will happen?

A

The AC power transfer switch will swap back to the normal source after a short time delay.

28
Q

What does DFWCS do if a Steam Flow Transmitter that has been placed in ‘maintenance’?

A

It doubles the value of the one remaining to generate a Total Steam Flow which is used to bias the Master Controller.

29
Q

Describe the Adaptive Tuning Logic (ATUN) in the DFWCS.

A

ATUN adjusts the controller responsiveness (gains, time constants) based on the values of Feedwater Temperatures and Reactor Power

30
Q

What does the DFWCS do with the inputs from Steam Flow Transmitters on its associated SG?

A

It adds them together to get Total Steam Flow which is used to bias the Master Controller.

31
Q

What flow mode is RTO designed to function?

A

Forced Circulation

In Natural Circulation the RTO Controller will likely overfeed the SGs (overcooling) due to the higher Tave associated with NC.

32
Q

How does the Reactor Regulator System (RRS) interface with DFWCS?

A

Provides Tave so DFWCS can determine if it should be feeding the SGs or not during RTO.

33
Q

What happens to DFWCS if NNN-D11 and NNN-D12 are both lost?

A

DFWCS will have no power

34
Q

How does SBCS interface with DFWCS?

A

Steam Bypass Demand along with TLI (Turbine Load Index [HP Turbine First Stage Pressure]) are sent to DFWCS to provide anticipatory transient control.

35
Q

What is the power supply to the DFWCS?

A

Normal power is NNN-D11 and NNN-D12 is the alternate power. Power will automatically swap to the alternate power if the normal supply is lost.

36
Q

What is the SGWL deviation alarm setpoint in the DFWCS?

A

10% deviation between the detectors on the same SG.

37
Q

How does biasing the speed signal affect the Main Feed Pumps?

A

Biasing changes the called for speed signal to the Main Feed Pumps.
Single Arrow = 10 RPM (1%)
Double Arrow = 50 RPM (5%)

38
Q

What is used to tune the proportional band and integration rate while DFWCS is in 1 Element Control?

A

Feedwater Temperature

39
Q

Describe the response of the DFWCS on a startup.

A

13% - indicated feed flow changes from the Downcomer to the Total Feed Flow transmitters
14% - DFWCS shifts from 1E to 3E
15%-16.5% - Swapover
50% - Downcomer Control Valves open to ~65% (

40
Q

On the way down, what are the requirements to perform Swapover?

A

Power < 15%

41
Q

When will the Master Controller go to “tracking” mode (i.e. display “tracking” on the screen)?

A
  • Anytime the Economizer and Downcomer Control Valves are placed in Manual
  • When a Reactor Trip occurs the Master Controller will track the output of the RTO Controller
42
Q

What controlling function do the Steam Flow Transmitters serve in the DFWCS?

A

Once steam flow > 50%, the Downcomer will open to pass 10% flow and will close if steam flow < 50%. These steam flow values come directly from the same transmitters DFWCS normally uses.

43
Q

If Total Feed Flow reaches __% deviation, DFWCS will swap to ___ Control and generate a _________ __________.

A

8%
1E
3E Lockout

44
Q

In reference to DFWCS, what is meant by the term “element”?

A
  • SGWL
  • Feed Flow
  • Steam Flow
  • When in 1 Element Control, SGWL is the controlling indication.
45
Q

When will DFWCS cycle in RTO after a Reactor Trip?

A

It will exit when SGWL > 51.9% NR and will re-enter RTO when SGWL < 26% NR. This will cycle until the under voltage relays on the CEDMCS bus are reset.

46
Q

At what Tave will all feed flow be stopped to the SGs after a Reactor Trip?

A

<564F

47
Q

Does a loss of a Foxboro controller affect the digital controller on the flat screen?

A

No. They control the same equipment but do not affect one another.

48
Q

If Feedwater Temperature reaches __% deviation, DFWCS will generate a _______ Lockout and ___________________.

A

8% (40F)
ATUN Lockout
insert a canned value of 425F

49
Q

What is Swapover?

A

The shifting of feed flow through the Downcomer to the Economizer on a startup or from the Economizer to the Downcomer on a shutdown.

50
Q

If Steam Flow reaches __% deviation, DFWCS will swap to ___ Control and generate a _________ __________.

A

50%
1E
3E Lockout

51
Q

How does ERFDADS interface with DFWCS?

A

ERFDADS provides lots of ‘indication only’ points to DFWCS.

52
Q

What specific transient does the RTO function in DFWCS protect against?

A

Overcooling of the primary coolant.

53
Q

Which NR SGWL transmitter on a SG does DFWCS select for use by the Master Controller?

A

The higher reading of the two transmitters on a single SG (even if its broken). There is no check on a high deviation between level transmitters on the same SG.

54
Q

How is the Total Feedwater Flow signal generated for the DFWCS?

A

Its collected from either one of the Feed Flow Transmitters or the average of the two if both are available.

55
Q

Describe how RTO works for DFWCS.

A

On a Reactor Trip, RTO will tell the DFWCS to feed the SGs based on Tave as opposed to SGWL. This keeps the DFWCS from rapidly refilling the SGs after the shrink which would result in overcooling and depressurizing the RCS.

56
Q

How does the DFWCS Master Controller behave during Swapover on a down power?

A

The Master Controller will be tracking even though it doesn’t indicate it on the display. It will indicate an “L” (local) during this time

57
Q

If SGWL reaches __% deviation greater than the _______ SG, DFWCS will swap to the ________ detector on the _________ SG.

A
  • > 15%
  • opposite
  • lowest
  • affected
58
Q

How does CEDMCS interface with DFWCS?

A

DFWCS receives input from the 4 under voltage relays on the CEDMCS bus (indicating a reactor trip) for determination on if it should be in RTO.

59
Q

Is the ATUN system more responsive at high powers or low powers?

A

High power

60
Q

How does changing the Control Channel NI input to DFWCS on the FWCS 1 Redundant Transmitter Logic screen affect DFWCS?

A

Changing the input changes the selection for BOTH DFWCSs.

61
Q

When does the DFWCS swap to 3 Element Control?

A

> 14% Reactor Power

62
Q

If Reactor Power reaches __% deviation, DFWCS will generate a ______ Lockout and _________ ________________.

A
  • 8%
  • ATUN
  • insert a canned value.
    • 5% if below 16.5%
    • 60% if above 16.5%

ZZ LOIT CWS Systems 2018 (35 decks)

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