Reactor Coolant Pumps Flashcards
What is the Functions of the RCPs?
- Transfer core heat to SG’s via forced circulation
- Heat up RCS to Hot Standby (HSB) conditions via pump heat
- Provide normal Pressurizer spray for pressure control
- Provide cooling flow to the reactor vessel head to prevent head void formation during cooldown
- Centrifugal pump rated for 92,500 gpm
What is the Design Basis of the RCPs?
- Non safety-related. Not required to achieve nor maintain safe shutdown conditions
- Can operate without cooling water for periods of up to 10 minutes without incurring seal damage
Discuss RCP Impellers.
Main: Circulates reactor coolant around the RCS loops. ~70 psid across pump
Aux: (integral to main) provides flow to hydrostatic bearing cavity (used for radial alignment of shaft)
Recirculating: Circulates 40 gpm lower cavity seal water through a seal cooler cooled by CCW
Discuss RCP Thermal Barrier.
Contains labyrinth seal around shaft circumference.
Cooled by CCW via drilled passages
Assists in limiting shaft leakage
Discuss the RCP Pump Casing.
Sealed by two flexitallic gaskets
Pressure Switch provides an alarm @ >2000 psia. Indicative of inner gasket leakage
Discuss the RCP Shaft Seal Cartridge assembly.
- Consists of four-stage mechanical seal which limits shaft seal leakage to acceptable levels
- Lower seal temperature >250°F can damage seals
Discuss RCP lower seal pressure drops.
Lower 3 seals drop pressure equally by thirds:
a) Lower cavity 2250 psia (RCS pressure)
b) Middle cavity 1365 - 1565 psia (1400 psia)
c) Upper seal cavity 615 - 815 psia ( 700 psia)
d) CBO cavity 65 - 150 psia (100 psia)
Pressure drop distributed evenly across lower three seals by capillary tubes, act as pressure-reducing devices
1% of flow passes between seal faces for cooling,
99% bypasses seal faces via capillary tubes
Discuss RCP Control Bleed-off Flow.
CBO flow: Normally about 1 gpm from each RCP, Goes to VCT
Each RCP CBO flow passes thru excess flow check valve which closes >10 gpm
Combined CBO return flow passes thru two CIAS valves which FC on loss of power/air
If these CTMT isolation valves close (CIAS), the Operator must open V2507 to unisolate the CBO relief valve (150 psig) which relieves to the Quench Tank
Alarm if CBO flow isolates
Discuss actions for RCP Seal Problems.
If CBO or lower seal cavity temperature reaches 250°F for 10 minutes or greater than 300°F at any time,
Then perform the following:
a) Trip the Rx and Turbine
b) Stop the affected RCP
c) Depressurize or cooldown the RCS as necessary to maintain CBO and lower seal cavity temp less than 250°F
Discuss RCP Vapor Seal.
Outermost barrier – Can hold 2500 psia during coast down and idle conditions
0.3 gph routed to floor drains - prevents Controlled Bleedoff leaking to atmosphere
Capable of holding 2500 psia DP with the RCP in a static condition
Discuss RCP Seal Cooling.
Each RCP CCW return line has an AOV which:
a) Closes if CCW return temperature > 200°F
b) Fails OPEN on Loss of IA OR Control Power
Annunciator Alarm: “Reactor Coolant Pumps Seal Tube Leak, Valve Closed”
RESET position of RTGB switch allows the valve to be re-opened after Tripping on High Temp.
Valve will re-close after 60 sec if High Temp condition still exists
Unit 2: Automatic reactor trip if total CCW flow to all RCPs < 1220 gpm for >10 minutes (2/4 logic)
{Unit 1 doesn’t have this trip but loss of CCW to RCPs is treated the same administratively}
Discuss RCP Seal Failure.
SEAL FAILURE: Defined as D/P < 100 psid across any seal
DEGRADED or DAMAGED SEAL: Seal parameters which are not normal but haven’t reached the failed seal criteria. Seal damage has occurred if seal cavity pressures are not equally reduced by approximately one-third of RCS pressure.
Low CCW Flow is only indicated by an Annunciator on Unit 1, flows on Unit 2
If CBO flow lost >30 minutes, trip reactor and RCP(s)
One seal failed - Take 30-minute readings and monitor
Two seals failed or CBO lost - Begin plant shutdown
Three seals failed - Trip reactor and RCP(s)
Discuss RCP Seal Injection.
- Not used since this has resulted in Cracked RCP Shafts at St. Lucie
Unit 1:
a) MV-02-1 ( Regen HX Bypass) is de-energized and OPEN when RCS pressure is greater than or equal to 1750 psia to ensure a flow path is maintained through MV-02-1, which has a Non-EQ motor.
b) Additionally, the valve position indication in the control room is powered from 120 VAC and the not the motor breaker, therefore there is indication with the motor breaker open. The Seal Injection lines downstream of MV-02-1 to the RCPs, are either isolated or removed.
c) MV-02-2 (Charging Line) is de-energized and OPEN with no indication in the control room Requires use of 1 additional Charging Pump, provided by CHG off upstream Side of the RHX
Unit 2:
a) Both V2598 (Charging Line) and V2185 (Seal Injection) are de-energized with V2598 OPEN and V2185 CLOSED. All the Seal Injection lines downstream of V2185 are isolated
Discuss RCP Motors.
Rated: 6500-hp @ 502 amps
Stator thermocouple and motor amps indicate on RTGB
Two motor air coolers cooled by CCW (cools air leaving the motor to limit temperature rise in CTMT)
Powered from 6.9 KV Buses A1 and B1
a) A1 powers RCPs A1 and B2
b) B1 powers RCPs B1 and A2
c) Loss of one 6.9 KV bus leaves RCPs running in opposing loops.
d) Loss of Offsite power leaves NO RCP’s running
Discuss RCP Anti-Reverse Rotation Device (ARRD).
Anti-reverse rotation device prevents reverse rotation of idle RCP when RCPs in other loops are operating
Limits the magnitude and duration of the starting current to prevent motor winding damage
Reduce reverse flow through an idle pump (bypass flow)
