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What is the minimum preferred pressure for starting a primary coolant pump?
- 250 psia is preferred
- -can be lowered to 235 psia
- --can have a problem with the seals staging properly
- Limit is set for cavitation
What are the PCP/CCW flow interlocks?
- If CCW flow is >80gpm, the PCP pump start interlock is satisfied
- >145 gpm for D PCP
What starts the PCP backstop pumps?
- The backstop pumps auto start when the lift oil pumps start, but remain operating after the lift pumps turn off
- Also auto starts when the PCPs are started
What are the PCP starting interlocks?
- ->/= 1700 psig lift oil pressure
- ->80 gpm CCW flow
- ->/=675 psig lift oil pressure
- ->145 gpm CCW flow
What are the PCP normal operating seal parameters?
- PCS pressure 2060 psia below the lower seal
- 1300-1400 psia after the lower seal
- 700 psia after the middle seal
- 20-100 psia after the upper seal
- If 1 seal fails then the pressure drop is 1030 psia per seal
- All seals are capable of withstanding full system pressure
- 4th seal is the vapor seal
- -designed to seal pressure when the pump is not rotating
What are the conditions requiring an emergency PCP shutdown?
- Pump bearing, seal, or controlled bleed off temperature reaches a predetermined setpoint
- -lower seal 185oF
- -controlled bleed off 185oF
- -any bearing high temperature alarm
- PCP vibration alarm accompanied by corroborating indications such as abnormal current, rising bearing temperatures, or a sudden change in PCS flow
- No PCP backstop pump is in service
- No CCW flow to containment for >10 minutes
What are the consequences of operating with PCP bleedoff pressure less than VCT pressure?
- Could have inadequate bleedoff flow which would cause damage to the seals
- Adjusted using a manual valve
P-50D anti-reverse rotation device
- Uses a ratchet and pawl system
- -as rotation is reversed a pawl grabs at the ratchet plate
What is the PCP flywheel operational design?
- Extends the coastdown of the PCPs upon a loss of all AC power
- -approximately 90 second coastdown from the flywheels plus the 10 second coastdown from the generator
- Aids in establishing natural circulation flow
- P-50D only has an upper flywheel
When are the PCP lift pumps started/stopped?
- AC or DC lift pumps are started 2 minutes prior to a PCP start.
- Also started 2 minutes prior to securing the PCP (AC pumps)
- Stop the pumps when PCP has stopped rotating (approximately 5 minutes)
What are the auto starts for the PCP DC lift oil pumps?
- DC oil lift pump will start if lift oil pressure is <1700 psig after 5 seconds if in auto and a PCP is not operating
- -<675 psig for P-50D DC lift oil pump
- They will auto shutoff after 5 minutes to protect the station batteries
- If PCPs trip, then the lift pumps auto start (AC pumps), if the AC pumps don't start, then the DC pump will start after 5 seconds and run for 5 minutes
What are the power supplies for PCP oil system pumps?
- AC pumps
- DC pumps
- Backstop pumps
What are the concerns with starting a PCP with S/G 2o side temperatures greater than PCS temperature?
Have a potential pressure transient
What is the reason for not operating P-50A and P-50B when the PCS is <300oF?
- Based on pressure in the reactor vessel downcomer region being greater with this pump combination
- -this could cause core uplift
What is the problem with running PCPs with less than normal temperatures?
Higher than normal vibrations
What is the backstop pump interlock?
The standby backstop pump will auto start if in auto and oil flow <0.24 gpm.
What are the PCP design parameters?
- Design pressure
- -2500 psia
- -2060 psia
- Design temperature
- Design flow
- -83,000 gpm each
- Maximum flow
- -110,000 gpm each
- Design head
- -260 ft
What is the purpose/design of the backstop device for P-50A-C?
- Prevents reverse rotation of the PCP
- -minimizes PCS bypass flow backwards through the pump
- -minimizes the duration of starting current
- -contains free wheeling clutches with inner and outer races and rotors and cams
What are the PCP breaker trips?
- Bus A/B undervoltage
- Breaker overcurrent
- Breaker differential
What is/are the PCP bleedoff flowpath/flowrates?
- Normally goes to the VCT
- If 4th stage seal fails, then bleedoff will go to the PSDT
- Flow is normally 1-1.25gpm at 125oF
What are the PCP power supplies?
- -A bus
- -B bus
What is the piggy back impeller?
Impeller that is mounted piggy back on the main impeller, provides forced circulation for the hydrostatic bearing and the differential pressure for the hydrostatic bearing.
What are the PCP oil system pumps?
- 2 oil lift pumps per PCP (1AC/1DC)
- -AC pumps
- -DC pumps
- 2 AC backstop oil pumps per PCP
- -P-50D does not have backstop oil pumps
What is the design of the thermal barrier?
- Mounted above the hydrostatic bearing
- Initially cools the primary coolant leaking along the shaft prior to entering the seal area
- Cooled by CCW
- Also tends to isolate the hot fluid from cooler fluid above
- In the event of a seal failure it acts as an additional barrier to reduce leakage from the pump
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