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Flashcards in Primary Coolant Pumps Deck (30)

What does the Piggy Back Impeller do?

Piggy back impeller: provides forced circulation and D/P for hydrostatic bearing


What does the Thermal Barrier do?

  • Provides initial cooling to the primary coolant leaking along pump shaft before it enters seal area
  • CCW is supplied in parallel to the thermal barrier and seal HX, and removes heat from pump and PCS fluid
  • Isolates hot fluid in the pump from the cooler fluid above, and serves as an additional barrier to reduce leakage in the event of seal failure


What does the Hydrostatic Bearing do?

Provides radial alignment􀀐􀀃 uses D/P across piggy back impeller to keep shaft centered􀀐􀀃 is cooled & lubricated by PCS fluid driven by piggy back impeller.


Describe the seal package ant its function?

  • Four seal cartridge assembly􀀐􀀃
  • Lower three seals divide the total press by the number of functioning stages
  1. Post Lower Seal ~ 1300 ‑ 1400 psia.
  2. Post Middle Seal ~ 700 psia.
  3. Post Third Seal ~ 20 ‑ 100 psia
  • Fourth seal is a vapor seal, but designed to seal against full system pressure when pump is not rotating
  • Cooled by CCW, minimum flow to seal is 35 GPM (counterflow HX))


What is controlled bleedoff?

It is Normal flow out of the seal package

  • Directed to VCT (not considered when directed to VCT).
  • CHP/CHR isolates VCT path. Flows to PSDT via RV-2082 (145 psia setpoint).
    • Flow may indicate 0 as flow instrument is bypassed.

Flow Rate

  • ~ 1 GPM
  • 1 Failed Stage: ~ 1.5 to 2 GPM
  • 2 Failed Stages: ~ > 2 GPM
  • All Failed ~ 30 GPM

Normal Temp after cooler is 130F, over 185F trip.



What is the lower oil reservoir?

  • A, B, C: 18 gal; D: 25 gal
  • 􀀐􀀃Lower guide brg submerged in oil; provides radial alignment
  • Temp and level indication on C-11 􀀐􀀃
  • Possible for upper sump leak into lower if lift pumps left running after securing PCP
  • Cooled by CCW


What is the upper oil reservoir?

A, B & C: 62 gallons (P-50D is 210 gallons)

  • P-50A/B/C only: Oil Lift and Backstop pumps take suction from this sump

Sump only filled to 80% to allow room to monitor for CCW in-leakage

Contains upper radial (guide) bearing and thrust bearings

"Slinger" device provides oil lubrication system pressure/flow when PCP running.


What is the purpose of the thrust bearings?

Depending on PCS pressure, the shaft will be supported vertically by the thrust bearings.

  • When PCS pressure is low (250 psia) the thrust is downward and is supported by the lower thrust bearing.
  • When PCS pressure is high (2060 psia) the thrust is upward and is supported by the upper thrust bearing.
  • The thrust transition between downward and upward occurs at approximately 1000 psia PCS pressure.


What are the AC lift pumps and their power supplies?

P-80 A/B/C/D 

P-80A/B – MCC-3

P-80C/D - MCC-4


What are the DC lift pumps and their power supplies?

DC Pumps, P-81 A/B/C/D

P-81A/C – 125 V DC Bus D-10L

P-81B/D – 125 V DC Bus D-20L


What is the function of the lift oil system?

  • Provides hydraulic force to lift (or push) thrust bearing away from thrust runner.
  • Reduces starting current duration.
  • AC or DC Oil lift pumps are started 2 minutes prior to PCS start/Stop.
  • PCP start interlock >=1700 psig oil pressure (675 psig for P-50D) and CCW flow >= 80 gpm (P‑50D >=145 gpm )
  • DC Oil Lift Pump will start if lift oil pressure <1700 (<675 P-50D) psig after 5 seconds, if in AUTO and a PCP is not operating. Has a 5-minute auto shutoff to protect the station batteries during a loss of all AC
  • P-50A, B, and C Oil Coolers receive a total CCW flow of ~ 55 gpm.
  • P-50D Oil Coolers receive ~ 105 gpm of CCW flow.


What is the function of the backstop / anti-reverse systems?

Device contains free wheeling clutches with inner and outer race and a compliment of rotors and cams on P‑50 A/B/C only. Minimizes PCS bypass flow backwards through pump and therefore starting current. Requires backstop oil pumps.

  • VERIFY vibration indicator for the Primary Coolant Pump to be started indicates less than 2 mils for no reverse rotation.

Anti-Reverse Rotation Device (P-50D only). Ratchet and pawl arrangement requires no lubrication, thus no need for a Backstop Oil Pump.


What is the function of the backstop oil system?

Backstop Oil System (P-50A, B, C only).

  • Provides lubrication for backstop device and backstop guide bearing

Each PCP two (2) pumps: P-83 and P-84

NO Control Room indication on pumps except low flow alarm (0.24 gpm).

P-50A, B, and C Oil Coolers receive a total CCW flow of ~ 55 gpm..

P-50D Oil Coolers receive ~ 105 gpm of CCW flow.



What are the power supplies and interlocks on the backstop oil pumps?

The backstop pumps will start and run whenever the “a” contact on either the PCP or HS associated with Oil Lift Pump breaker is closed.

If PCP is OFF:

  • AC Oil Lift Pump started, P-83 will start: Power Supply MCC-2
  • DC Oil Lift Pump started, P-84 will start: Power Supply MCC-7

Standby pump will AUTO start on low flow (0.24 gpm)

  • Lo flow alarm clears if B/U pump starts and provides adequate flow.
  • Running pump loses power, backstop low oil flow alarm will not clear.
  • 2.4 amps per breaker indicate 3 pumps are running.


What are the power supplies, starting and running current for PCPs?

A/C PCPs from A Bus

B/D PCPs from B Bus

P-50A, B, C – 670 Amps running. 4620 starting

P-50D – 687 Amps running; 4139 Starting

5500 Hp


What are primary coolant pump starting interlocks?

P-50A, B and C

  • >=1700 psig Lift Oil Pressure
  • > 80 gpm CCW flow


  • >= 675 psig Lift Oil Pressure, P-50D
  • >140 gpm CCW flow

No Control Room Guages. Use white permissive light "ON" and absence of CCW low flow alarms.



Describe the PCP vibration monitoring.

Four dual monitors, one for each pump

  • Each provides dual vibration monitoring (Channels A & B)
  • One common “Vibration Alert/Trouble” and one “Vibration Danger” alarm for all 4 pumps
  • Red lights for Danger/Alert for each channel
  • Flashing red light is “first out” indicator


What are the primary coolant pump breaker trips?

Bus 1A/B Undervoltage

  • Loss of A or B Bus results in spray flow going to 40%

Breaker overcurrent

Breaker Differential


What is the minimum pressure for starting a primary coolant pump?

Minimum PCS pressure for starting first PCP: 

  • 250 psig
  • 235 if NR selected on PI-0104


What primary coolant pump parameters require a reactor trip?

􀀐􀀃 Any PCP lower seal temp > 185F
􀀐􀀃 Any PCP CBO temp > 185F
􀀐􀀃 Any PCP bearing temp >175F


Why should P-50A/B not be run simultaneously when PCS <300F?

Press in Rx downcomer region is greater with this pump combination


What is the ramification of temperature differences between the SG and PCS on starting first PCP ?

To minimize pressure transients, the S/G water temperature should be as close as
possible and slightly lower than the PCS temperature. Heating the PCS
approximately 5F to 15F greater than the last obtained S/G temperature is the
preferred way to obtain this temperature difference.


What are the PCP starting limits?

P-50A , B, and C Starting Limitations:

  • Three starts in succession with the motor initially at room temp OR
  • Two starts with the motor at a temp that does not exceed NOT
    • Not considered > NOT when motor has been running >=20 min or idle >= 40 min

P-50 D Starting Limitations:

  • 􀀐􀀃Two starts in succession provided pump is permitted to coast down between starts
  • A third start may be made when the winding and core have cooled by running for >=20 min or the motor has been standing idle for >=45 min


What are the concerns with VCT pressure greater than Bleedoff pressure?

If Controlled Bleedoff pressure is less than VCT pressure reverse flow can occur.  This can cause damage to the PCP seals.


More than one seal failed, then what?

If more than one stage on a PCP Seal has failed or all seal Controlled Bleedoff flow
is stopped, then declare the PCP inoperable and place the Plant in Mode 3 within six
hours in accordance with Technical Specifications LCO 3.4.4.A.


What happens with the PCP Vibration Alarm of Danger?

The PCP vibration monitor "Danger" setpoint does not represent a physical limit
beyond which failure will occur, but a margin against imminent failure. It is
appropriate to monitor performance at or near this level and see if vibration is getting better or worse

Trip above 29 mils


When is a PCP stopped under Emergency conditions?

  • Pump bearing, seal, or controlled bleed-off temperature reach a pre-determined setpoint
  • PCP Vibration alarm accompanied by corroborating indications such as abnormal current, rising bearing temperatures, or sudden change in PCS flow
  • No PCP Backstop pump in service
  • No Component Cooling Water flow to Containment for > 10 minutes

Lift Pump Start NOT Required.


What happens to Bleedoff on Containment Isolation?

During CHP/CHR, controlled bleed-off is isolated from VCT, so drain path is to Primary Drn Tk via RV-2082 (145#)


How is PCP/Loop operation during Mode 3 & 4?

If the Plant is in Mode 3 or Mode 4, then all PCPs and SDC trains may be stopped
for up to one hour within any eight (8) hour period provided all of the following
conditions are satisfied:

  1. The cumulative time all PCPs and SDC trains are stopped is logged on the LCO Board until the eight (8) hour period is reset by operation of PCPs or SDC trains for a continuous eight (8) hours.
  2. No operations are permitted which would cause a reduction of PCS boron concentration.
  3. Core outlet temperature is maintained at 10F below PCS saturation temperature.