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Flashcards in Pressurizer Pressure Control Deck (23)

What is the purpose of the Pressurizer Pressure Control System?

Designed to maintain and control the Primary Coolant System (PCS) pressure 2010 psia to 2100 psia during power operation. through the use of a Pressurizer, where steam and water are maintained in thermal equilibrium.

Also provides overpressure protection for the PCS when the system temperature is below 430º F


How do PIC-0101A and PIC-0101B function?

Maintains pressure 2010 psia to 2100 psia during power operation

AUTO - normal mode of operation

  • Operator selects setpoint and controller sends signal for more/less spray/heat.


  • Operator changes output via slidebar.
  • SLOW (either < or >) will cause the signal to change at 2.5% per second. 
  • FAST (either << or >>) causes the signal to change at 25% per second.


What occurs with varying signal output from PIC-0101A/B?

0% to 33.3%

  • Proportional Heater vary from full on to off.

66.6% to 100%

  • Spray varies from closed to full open.

33.3% and 66.6%

  • Proportional Heaters and Main Sprays Valves are off and closed


What are the controls and indications for PIC-0101A/B?

RED Light Lit - Failure, call I&C

AMBER Light Lit - Alarm, plant below 1500 psia or call I&C

CASCADE - no function

RED (left) Pointer - indicates system pressure

BLUE (right) Pointer - Operator controlled setpoint

AUTO - pushing places controller in Auto

MANUAL - pushing places controller in manual

BOTTOM SIGNAL METER - output of controller


What are the power supplies to PIC-0101A/B?

PIC-0101A - Y10.

PIC-0101B - Y20.

PIC fails to 0% output upon loss of power to the controller (heaters fully on).


What is the purpose of 1/PRC-0101, Control Selector?


Select PIC-0101A or PIC-0101B for output to Spray/Heaters

Unselected Pressurizer pressure controller is MANUAL, with a 50% output signal.

  • Prevents saturating unselected controller


What is the function of the pressurizer heaters?

Maintain thermal equilibrium at approximately 640º F (Tsat for 2060 psia)

To limit the pressure drop and restore pressure to controller set point during transients and normal operations.

Sized to heat up the PZR at zero power programmed level at a rate which maintains about 200 psia subcooling as the PCS is heated by decay heat and pump heat.

One half of the heater capacity (nominally 750 KW) provides sufficient capacity to establish and maintain natural circulation in hot standby conditions.


What are the Pressurizer Heater Groups and power supplies?

Backup heaters - four groups.

  • Groups 1 and 3
    • 24 heaters.  Rated at 300 KW/group.
  • Groups 2 and 4
    • 30 heaters.  Rated at 375 KW/group.
  • Group 3 & 4 Power Supply
    • D Bus via LCC 16
  • Group 1 & 2 Power Supply
    • E Bus via LCC 15


What is the ouput of the pressurizer heaters? What is T.S. requried?

12.5 KW. / heater

1500 KW for all heaters (Proportional and backup).

Normal power consumption is 145 amps for each LCC 15 and 16

PZR heater capacity of 117.5 amps on each Heater Transformer (LCC 15 and LCC 16) is required to satisfy Technical Specification LCO 3.4.9 b and c to have greater than or equal to 375 kW of Pressurizer heater capacity on bus 1D and bus 1E.


What are the backup heater controls and indications?

  • C-02 Handswitch - OFF/AUTO/ON
  • Auto - not used
  • Green Light - heaters off
  • Red Light - heaters on
  • Controled in manual - backup heaters on
  • Amp meters on C-02: Normal is 145 amps for each LCC 15 and 16.


What is the Proportional heater control?

Proportional heaters

Two groups with 6 heaters/group.

Voltage Regulation based on signal from PIC-0101A/B

  • 0% - Full Power
  • 33.3% - Off

Proportional heater Handswitches (Group 1, 2):

  • OFF: Heaters breakers are open.
  • ON: Heater breaker closed and heater output controlled by output of PIC.

Proportional heater indication lights:

  • GREEN (off), RED (on)


What is the Pressure Control Strategy?

Backup Heaters On (in manual)

Pressurizer held steady at 2060 psia

Controller Output - 66%


  • Quicker spray response; therefore little pressure cycling of PZR pressure.
  • Better boron mixing or less boron concentration differential between the PZR and PCS


What is the Pressurizer Heater Level Trip?

Pressurizer Level Heater Trip

36% - Heater Control Selector switch trips heaters

Heater breaker from Bus 1E (LCC‑15), will reclose when Pressurizer level > 36%

Heater breaker from Bus 1D (LCC‑16), will NOT reclose when Pressurizer level > 36%

  • Diesel Generator sequencer could be loading the Diesel Generator and the Pressurizer Heaters are NOT part of the sequence.



What is the design and motive force for CV-1057, CV-1059?

CV-1057, CV-1059

Parallel 3" air to open spray control valves.

Combine into a single four-inch line connected to a single spray head.

¾” flow adjustable manual bypass valve throttled to approximately 1 gpm flow.

  • Reduces thermal shock to the Pressurizer spray lines and surge line and minimizes differences in boron concentration between Pressurizer and PCS.




What loops are the spray valves off of and what is spray flow under varying conditions?


  • PCS Loop 1B


  • PCS Loop 2A

Spray Flows

  • Both spray valves - 375 gpm.
  • One spray valve - 280 gpm.
  • One Spray valve open will overcome the heat input from all Heaters ON.
  • One PCP operating in each loop, spray flow is reduced to 40% of maximum flow.
  • One spray valve isolated, spray flow is reduced to  70% of maximum flow.
  • One PCP operating in each loop and one spray valve isolated, the pressurizer spray flow is reduced to approximately 30% of maximum flow.


What are the controls and indications for CV-1057/1059?

Spray Valve Handswitches (CV-1057/1059):

  • CLOSE: Valve closed.
  • AUTO: Positioned from output of PIC-0101A/B.

Spray Valve indications (CV-1057/1059):

  • Green: valve closed.
  • Red: valve open.
  • Green and red: valve throttled


What is Auxiliary Spray Control Valve (CV-2117)?

Auxiliary Spray Control Valve (CV-2117)

Air to Open (Open/Closed no throttling)

On 2-inch line from charging pumps

Used during startups/shutdowns or for pressure control during natural circulation, i.e., PCPs NOT available.



What are the requirements for logging spray cycles?

If Pressurizer sprays (main or auxiliary) are operated when differential temperature
between spray water and Pressurizer vapor phase is greater than 200F, then
perform the following:


  • Log the time, differential temperature, and Pressurizer pressure in the NCO Turnover Items book and the narrative logs.
  • A cumulative total of spray cycles with greater than 200F differential temperature shall be kept in the NCO Turnover Items book.
  • The abnormal operating limit for differential temperature is 350F, but may be exceeded in an emergency situation.
  • Initiate a Condition Report for Engineering to track the number of thermal cycles on the Spray Line.


What is LTOP?

Low Temperature Overpressure Protection Operations (LTOP)

  • Overpressure protection for the PCS, when the system temperature is below 430º F,
  • System utilizes the power operated relief valves (PORVs) to relieve pressure in excess of the limits imposed by reactor vessel brittle fracture restrictions. 
  • The PORV setpoint can be a fixed or variable and is a computer-determined value dependent on PCS temperature. 
  • The major components are the PORVs and the LTOP control units.


What are the LTOP Control Units (PY-0105A and PY-0105B) and their power supplies?

PY-0105A and PY-0105B

Calculates a pressure setpoint based on cold leg temperature.

Will actuate the PORVs if the calculated pressure setpoint is exceeded.

Power Supplies

  • PY-0105A, Y‑30
  • PY-0105B, Y‑40
  • Loss of power renders channel unavailable.


What are the inputs into LTOP?

PT-0104A/B, Pressurizer Narrow Range Pressure - Low Range

  • Initiate opening of the PORVs on LTOP signal

PT-0105A/B, Pressurizer Wide Range Pressure

  • Redundant wide range pressure channels inputs to the LTOP system.

TT‑0112CA, Cold Leg Temperature

  • Input to TS‑0115, LTOP Temperature Switches (Channel A).
    • Provides temperature input signal which enables automatic operation of the LTOP system
    • Provides an alarm if LTOP is not in service prior to an established temperature limit.

TT-0122CB, Cold Leg Temperature

  • Input to TS‑0125, LTOP Temperature Switches (Channel B)
    • Provides temperature input signal which enables automatic operation of the LTOP system
    • Provides an alarm if LTOP is not in service prior to an established temperature limit.

'A' Channel inputs into PY-0105A.

'B' Channel inputs into PY-0105B


What is the LTOP use of temperature input?

The LTOP computer in the shutdown-cooling mode does NOT use the temperature input to LTOP, but that failure of the temperature input will render the LTOP channel out of service.

The LTOP logic is designed to prevent any automatic actuation with a failed temperature input.