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ILOT > Reactor Recirculation and Flow Control - 1.0 > Flashcards

Reactor Recirculation and Flow Control - 1.0 Flashcards

1
Q

What affects does Recirculation flow have on plant reactivity and the boiling boundary?

A

Changes plant reactivity in the same direction as the flow rate change and moves the boiling boundary up or down in the same fashion.

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2
Q

What cools the Recirc pump motors?

A

RACS

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3
Q

How is the Recirc system affected upon a PCIS isolation signal? Are there any follow-up actions required?

A

RACS cooling isolates on a PCIS signal but the Recirc pumps do NOT trip. AB.COOL-3 and AB.RPV-3 requires the observation of several temperatures and followup actions based on these indications.

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4
Q

Describe the layout of the Jet Pumps.

A

20 Jet pumps. Ten groups of two jet pumps connected by a RAMS head.

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5
Q

Are there chemistry/RP requirements for power alterations?

A

following runbacks (TS 3.4.5/3.11.2) (Samples required for 15% change in 1 hour)

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6
Q

What Recirc system interlocks are associated with the pump suction valves?

A

a) Must be full open to start Recirc pumps.
b) Trip Recirc pump if <90% open.

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7
Q

What is the max rated D/P and associated timing for proper operation of the recirc pump suction valve?

A

50 PSID for 30 second stroke time

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8
Q

What is the max rated D/P and associated timing for proper operation of the recirc pump Discharge valve?

A

200 PSID for 30 second stroke time, however the opening of the discharge valve is sequenced with delays resulting in an actual opening time of 80 seconds

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9
Q

What are the conditions that cause an Intermediate Runback?

A
  • Loss of 1 Circ Water pump w/ 4 running and condenser pressure >4.5”HgA.
  • Loss of 1 RFP w/ RPV water <Level 4(+30”).
  • Loss of 1 PCP or SCP w/ with feed flow ≥73.65% AND ≥2 RFPs in service..
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10
Q

What Recirc system interlocks are associated with the pump discharge valves?

A

VFD will trip under the following conditions:
1. Discharge valve must be ‘not 100% closed’ (OPEN light illuminated) 3 seconds after receipt of a DRIVE RUNNING signal from the VFD which occurs when the pump is running at 20% speed
2. Any time the discharge valve is not at least 90% open 85 seconds after DRIVE RUNNING signal

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11
Q

What are the conditions that cause an Full Runback?

A
  • RPV water level <Level 3 (12.5”).
  • Total feed flow <22% for >15 secs.
  • Loss of 1 Circ water pump w/ 3 or less running AND condenser pressure >5.8”HgA.
  • Loss of Stator water cooling after a 12 sec TD as sensed by:
    1. Inlet pressure low-low (64#)
    2. High Temp (79°C)
    3. Low Flow (690 GPM)
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12
Q

Describe the conditions that will cause a Recirc pump Trip.

A
  • Disch. VLV not off its shut seat 3 seconds after reaching 20% speed.
  • Disch. VLV <90% open. Bypassed for 85 secs on pump start.
  • Suction VLV <90% open.
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13
Q

Describe the Jet Pump Subtraction Circuits purpose.

A

During single recirc loop operation(defined by the DRIVE RUNNING signal and discharge valve position), if operating loop flow is sufficient (> 23,000 gpm{48% flow}) the idle loop will experience reverse flow through its associated jet pumps.

This circuit compensates by subtracting the equivalent reverse flow from the operating loop flow.

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14
Q

Describe the valve ratings.

A
  • F023 (Suct.) rated to shut at 50 psid.
  • F031 (Disch) rated to shut at 200 psid.
  • When isolating Recirc Pump, shut suction valve first because of this D/P.
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15
Q

Describe the Jet Pump Subtraction Circuits operation and how it knows when to operate.

A

> 48%(23,000gpm) operating loop flow - subtraction circuit
<48% - loop flows added together by operator(SPDS is inaccurate)

The circuits operation is base on the DRIVE RUNNING signal and discharge valve position

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16
Q

What is 100% core flow?

A

104Mlbm/hr summed through the jet pump loops

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17
Q

List the components of the recirc pumps that are cooled and their mediums.

A
  • Motor air cooler (Windings) - DW chill water.
  • Motor oil cooler - RACS.
  • Seal Cooler - RACS.
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18
Q

Describe the Recirc seal indications if they fail.

A

(a) 1st seal:
PT for 2nd Cavity >500#
Seal staging flow Hi
(b) 2nd seal:
Seal staging flow Low
Last seal leakage Hi
(c) Both Seals:
PT for 1st Cavity 0#
PT for 2nd Cavity 0#
Seal staging flow Low
Last seal leakage Hi

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19
Q

What is the maximum seal leakage flow and why is that the limit?

A

60 gpm leakage due to internal bushing

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20
Q

What are the RPT Breaker Trips?

A

1) End-of-cycle trip
2) ATWS Trip
3) Overcurrent

21
Q

What causes the End-of-cycle trip for the RPT Breakers

A

a) Turbine stop valve closure <95% open
OR
LOW EHC oil pressure (TCV closure) less than or equal to 530 psig
WITH

b) Power ≈18% or greater as indicated by turbine first stage pressure >98.1 psig

22
Q

Describe the ATWS Trip for the RPT Breakers.
(RRCS Interrelationship)

A

a) Low-Low reactor water level less than or equal to -38” with 9 second time delay, OR
b) High reactor pressure greater than or equal to 1071 psig

23
Q

What indications would you see if the recirc pump seal orifices are plugged?

A

Orifice #1 plugged - #2 seal pressure drops and stage flow drops.
Orifice #2 plugged - #2 seal pressure rises and stage flow drops.

24
Q

On a Recirc Seal pump leak, what valve should be closed first and why?

A

suction closed first to minimize diff press across the suction valve

25
Q

How can you operate the RPT Breakers?

A

The breakers can be closed from the control room (10C651) but the TRIPPED control bezel is an indicating light only.
Each RPT cubicle has a three-position (Pull-to-lock, trip, close) control switch
Breaker can be closed from the control room but can only be opened via the local control switch or EOC-RPT/ATWS trip

26
Q

What is the bases behind the EOC RPT trip?

A

At EOC, the reactivity feedback due to pressurization transient can add (+) reactivity faster than rod can add (-) reactivity. Tripping the RR pumps rapidly reduces coolant flow which increases voids. Designed to counteract the effect of CV’s and TSVs shutting.

27
Q

What are the conditions required for an EOC RPT trip?

A
  • TSV <95% open
    OR
  • TCV fast closure <530 psig ETS at the valve control pac
    WITH
  • Power ≈18% or greater as indicated by turbine 1st stage pressure >98.1 psig
28
Q

What can occur is Manual Speed Hold is active prior to runback initiation?

A

No runback will occur if Manual Speed Hold is active prior to automatic OR manual speed runback is initiated.

29
Q

If the raise or lower pushbutton on a VFD sticks, what is the result to the VFD?

A

Each speed command is a discrete pulse which requires a release between successive commands. If a RAISE/LOWER pushbutton sticks, only the original discrete speed change command will be sent. After 10 seconds, the STUCK BUTTON input will be removed. This causes the control system to ignore inputs from this button until MANUALLY reset(not a speed hold action)

30
Q

What is the maximum number of cells that can be bypassed in the VFD?

A

6 of 12

31
Q

What occurs on the failure of a VFD cell?

A

a speed reduction of approximately 100rpm due to the time for the fast cell bypass to short out the failed cell

32
Q

What is the primary NGX controller and what occurs as a result of a fault in this controller?

A

A NXG controller is primary and upon its loss, control will shift to the B NXG controller after a .5 sec time delay. This also results in a speed reduction due to the temporary loss of power.

33
Q

What is the lowest percent flow that can be achieved by the recirc pumps?

A

Speed cannot be manually lowered <20%, however if it automatically lowers to <20% but >18%, it will automatically restore to 20%. If instead, it lowers to <18%, the VFD will trip.

34
Q

If the recirc pump is tripped via the 7.2 kV input breaker TRIP pushbutton, what is required to restore the pump to operation?

A

The drive will consider this a fault, and will required local operation of the Latched Fault Reset key to restart the pump

35
Q

What occurs when the START PRECHARGE pushbutton is pressed? Is there a requirement for this process to start?

A

The VFD must be in a RDY PRECH state. Once the process starts it preforms the following:
1. Input power testing
2. Capacitor and resistor banks are disconnected as power is connected
3. Cell diagnostics occur and once complete
4. PRECH COMP illuminates and
5. The 7.2 kV input breaker closes

36
Q

Does the Precharge routine in the VFD verify external interlocks? If so, when does it occur?

A

It does not verify the following interlocks associated with the 7.2 Input breaker are met:
a) Suction valve open
b) Discharge valve shut
c) RPT breakers shut
if a precharge is started without these interlocks met you will get a precharge fault when the breaker fails to close.

37
Q

Where are automatic and manual runbacks generated?

A

Auto Runbacks are created EXTERNALLY and manual runbacks are created INTERNALLY.

38
Q

How does a runback affect the raise speed pushbuttons for the VFDs?

A

The RAISE speed pushbuttons are disabled while a runback is present and speed is above the runback setpoint.

39
Q

How does a runback affect the raise speed pushbuttons for the VFDs?

A

The RAISE speed pushbuttons are disabled while a runback is present and speed is above the runback setpoint.

40
Q

How does a runback affect the lower speed pushbuttons for the VFDs?

A

It does not, the LOWER speed pushbuttons are NOT disabled during a runback and WILL reduce the Speed Demand below the runback setpoint.

41
Q

When/how are automatic runbacks reset?

A

They seal-in until the condition is clear AND the Control Room resets the runback by pressing the associated runback pushbutton

42
Q

When/how are manual runbacks reset?

A

Manual R/B are automatically reset once the R/B speed limit is reached OR a speed hold occurs

43
Q

How does a speed hold affect runbacks?

A

Speed Holds can inhibit or suspend an Automatic and manual Runback.(ie if in progress it will stop it and keep it at the current speed value)

44
Q

Under what conditions will a speed hold not affect the VFD automatic/manual operations?

A
  • Speed Holds have no effect when the VFD is operating in LOCAL mode.
  • If a Cell Bypass or NXG control switchover to backup occurs during a Runback, a Speed Hold will not be issued until the runback reaches its setpoint.
45
Q

What is the sequence after you press the Start Precharge PB?

A
  • Backup then normal controller precharge sequence.
  • VFD bkr closes.
  • Start PB & pump ramps up to 30%.
  • After 20% speed, RUNNING illuminates.
46
Q

What are some VFD Trips?

A
  • If both the level switch and the transmitter sense a coolant tank level low low level (15%).
  • No cooling pumps and secondary thermal alarm.
  • Hi temps on cells & transformer.
47
Q

What can happen if a PB is held too long?

A

If a PB is depressed >10 secs it rejects any further operations until the fault reset PB is depressed.

48
Q

What can happen if a PB is held too long?

A

If a PB is depressed >10 secs it rejects any further operations until the fault reset PB is depressed.

49
Q

What will a loss of a flow transmitter cause?

A

APRM upscale trips(for the channel) based on a power to flow

ILOT (93 decks)

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