CF-IFC Flashcards
Purposes of CF-IFC Integrated Feedwater Control
o Provides the required feedwater to maintain a programmed water level in the SG as a function of power level
o Protect against excessive reactivity additions and containment pressure on a steam line break
o Prevent turbine damage from water carryover
What is …
o Change in level due to a change in the average density of the water/steam mix in the SG
o At power increased boiling causes the water in the downcomer region to go up in level as the steam pushes down on the water in the boiling region
Shrink and Swell
SG mix/max’s Limiting mass are required to?
Minimum mass required to prevent the tubes from being uncovered
Max mass required to limit the potential cooldown from a steam line break (more mass in SG at lower power levels, worse RX effect then)
Reasons for a S/G Max water level
Keeping water out of steam lines
During a tube rupture high level could lead to a release outside of containment
Level set to program level to compensate for shrink and swell
Based on median select 2nd highest NI power level
If one channel below the lo-lo setpoint (17%) alarm generated
If either one of channels 3 or 4 above hi-hi setpoint (83%) alarm generated
SG level
what are the IFC Inputs?
NI power level - Based on median select 2nd highest NI power level
SG Level error - Median select 2nd highest from NR detectors
Compared to NI power level, generate the + or – 5% deviation alarm
Steam flow Feed flow mismatch
Feed Flow - 3 channels per SG with square root extractors to get mass flow rate - Median select uses all three channels
Steam Flow - 2 channels per SG with square root extractors and density compensation
Arbirtated average used (deltaT used)
Mismatch
• Selected steam flow – Selected feed flow
• 20% less steam or feed flow will generate an alarm for each case
Low vs High power control modes
In power increase
In power decrease
Low power
In power increase, mode active until 18% CF flow
In power decrease, mode active below 13% CF flow
WR detectors with a level error multiplied by 1.5 used
• Multiplication makes low power mode dominate
• Compared to NR level and outputted
High power
In power increase, mode active after 18% CF flow
In power decrease, mode active until 13% CF flow
Has a gain applied from selected SG water temp (all 4 SG’s combined water temp)
Feedwater control Program
When does the bypass valves close coming up and going down?
Recirc flow based on suction flow
• Average of two suction flow instruments with a third instrument to be arbitrator
Bypass valves closed at 30% (coming up) and 75% (coming down) to avoid AMSAC
Speed control
Highest feedwater demand signal from all 4 SG’s used (the one that needs water the most)
Automatic Modes
• Speed set mode maintains the CF pump at a operator entered RPM
o Used to start the CF Pump and accelerate up to 3900 rpm
• Auto mode maintains pump sped based on the feedwater demand signal
o Must be over 3600 rpm to meet interlock to use Auto mode
FP A/B Above Min Speed Condition
In Manual, CF pump low and high pressure governors both manually controlled
Actual pump speed comes from 5 speed signals
• The first three go into a median select as do the last three
• The outputs from the median selects are averaged
On a P-4 Rx Trip both feed pumps go into ‘rollback hold’ at 2800 RPM
• The CF pump will go from speed set into auto mode when the P-4 signal comes in
• After 105 seconds, the CF pump will go into speed set mode
What are possible SG Transmitter failures?
o SG level are wet leg with condensing pot type
o Break in reference leg
Removes high pressure side failing transmitter low (DP down)
o Low level in reference leg
Lowers the top value, looks like a level increase
o Hostile environment in containment
Increased reference leg temp will expand water resulting in mass loss, indicated higher than actual
o Break on SG line to transmitter (low pressure/process side)
Low side pressure goes away, max DP min Level
o Rupture in transmitter diaphragm
DP = 0, max level
