Digital Feedwater Control (DFWCS) Flashcards
When will the DFWCS Master Controller enter and exit tracking on a Reactor Trip?
Exits at >51.9%NR SGWL
Enters at < 26%NR SGWL
If the 1E button on the DFWCS Screen is green and power is raised > 14% what will happen?
DFWCS will NOT automatically swap to 3E. One of the prerequisites to swap is that the 3E button is green (selected).
When does DFWCS swap from 3E to 1E?
13.5% and decreasing
What causes an “ATUN Lockout”?
8% deviation between Reactor Power instruments or
8% deviation between Feedwater Temperature Typically a transmitter failure will be the cause of this.
Describe the response of the DFWCS on a shutdown.
100%: DCCVs passing 10% flow, ECCVs maintaining SGWL
50% - Downcomer Control Valves close
15% - Swapover (ECCVs immediately close. DCCVs immediately open to 20% then ramp to 80%)
13.5% - DFWCS shifts from 3E to 1E
13% - indicated feed flow changes from the Total Feed Flow transmitters to the Downcomer.
What is High Level Override in the DFWCS?
When SG is too high (>88%NR), the DFWCS will close the Downcomer and Economizer Control Valves in an attempt to lower SGWL.
- ≥ 88% NR
- Closes feedwater control valves on affected SG (Downcomer and Economizer)
- Sends a “zero” signal to MFP controller on the affected SG FWCS.
What is the power supply to the DFWCS?
**Normal power is NNN-D11 **and NNN-D12 is the alternate power. Power is normal-seeking.
(Loss of NNN-D11 will cause the following:
o Loss of one Reactor Power input (Excore Control Channel #1) Low TAVE will cause DFWCS to NOT feed in RTO
* Loss of NNN-D12 will cause the following:
o Loss of one Reactor Power input (Excore Control Channel #2) Low TAVE will cause DFWCS to NOT feed in RTO)
Describe the response of the DFWCS on a startup.
< 13%: ECCVs closed, DCCVs maintaining SGWL, MFPs at minimum speed, 1E Control
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%
When will the Master Controller go to “tracking” mode (i.e. display “tracking” on the screen)?
- 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
If Total Feed Flow reaches ______% deviation, DFWCS will swap to ___ Control and generate a _________ __________.
8%
1E
3E Lockout
When will DFWCS cycle in RTO after a Reactor Trip?
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 (UV 1&2 OR 3&4) bus are reset.
At what Tave will all feed flow be stopped to the SGs after a Reactor Trip?
Less than 564F
If Feedwater Temperature reaches ___% deviation, DFWCS will generate a _______ Lockout and ___________________.
8% (40F)
ATUN Lockout
insert a canned value of 425F
If Steam Flow reaches ____% deviation, DFWCS will swap to ___ Control and generate a _________ __________.
50%
1E
3E Lockout
MFP Arrow control - How big are the increments for a single arrow push vs. a double arrow push?
- Manual Control
o Single arrow - 1% change (10 RPM), Double arrow - 5% change (50 RPM)
If Reactor Power reaches _____% deviation, DFWCS will generate a ______ Lockout and _________ ________________.
- 8%
- ATUN
- insert a canned value.
- 5% if below 16.5%
- 60% if above 16.5%
What are the “Elements” in 1E vs 3E control in Digital Feedwater Control System?
1E = Steam Generator Level
3E = Steam Generator Level + Steam Flow + Feedwater Flow
How does the Steam Bypass Control System support the Digital Feedwater Control System?
Steam Bypass Control System
* SBCS Demand (output) and TLI provide anticipatory transient control. (Reliable indication of steam demand.)
* 1E controller only.
When RTO (Reactor Trip Override) logic clears, what is the status of the Digital Feedwater Control System (DFWCS) master controller (auto or manual)?
- When RTO logic clears, at ≥ 51.9% (NR), then the master controller will shift to 1E control (in “auto”).
- Even if the master controller was in “manual” at the time of the trip, it will be in “auto” when the RTO logic clears.
What happens to the master controller on a reactor trip?
- Master controller shifts to “local” and “tracking” on a trip.
- Will track, and pass, the signal from the RTO controller. Controller will be in “tracking” as long as the RTO logic is present.
How many Steam Generator Water Level transmitters does DFWCS use? How does it pick a transmitter to use?
- Control function in 1E and 3E (4 total transmitters, two for each generator)
* Auto selects the highest reading Level Transmitter on a SG - If one is OOS, uses the remaining LT
-
15% deviation between SGs:
o Selects the lowest LT for control on the SG that has the higher level
What event does RTO prevent?
When the reactor trips, SG levels normally will lower rapidly due to the shrink caused by an increase in steam header pressure. DFWCS (in RTO) will feed
the SGs much more slowly than the large level deviation from setpoint would call for. RTO
prevents an overcooling transient.
During natural circulation (loss of RCP’s), RTO will overfeed.
How does DFWCS compensate for a steam flow transmitter being placed in maintenance?
If a steam flow transmitter is removed from service by placing it in “maintenance” on the FWCS 1
Redundant Transmitter Logic screen, the remaining transmitter’s value will be doubled in order to approximate total steam flow and that value will be used by 3 element control.
Is Control Channel adaptive tuning used in 1E control in DFWCS?
No
Uses Average of the inputs
o Can select either channel or average on DFWCS (only FWCS 1)
* Tunes the responsiveness by adjusting the proportional band and integration rate based on the reactor power level.
o More responsive at higher power levels. (3E only)
