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Flashcards in CRHV Deck (57)

Explain the purpose of the Control Room HVAC System

Maintain the

  1. Control Room
  2. Tech Support Center
  3. Viewing Gallery
  4. and Mechanical Equipment Room environments

Suitable for continuous personnel occupancy and reliable equipment operation under all conditions


Is the control room HVAC safety related?



What are the functional capability and design features of the CRHVAC?

  1. Maintained at a positive pressure (vestibule doors part of this).
  2. Limit radiation exposure of Control Room Personnel during any of the postulated DBA(s) within the guidelines of 10CFR50, Appendix A, General Design Criterion 19.
  3. Single active component failure, even with loss of off‑site power, cannot impair the system's ability to meet its design function.
  4. Permits rapid purging of smoke.
  5. Remain functional during and after earthquake (seismic).
  6. Remain functional during and after a design basis tornado.
  7. Maintain temperature and humidity within recommended comfort zone.
  8. Permit periodic inspection, testing and maintenance.


What components make up the over overall CRHVAC system?

Two trains of

  • Air Handling/Filtering Units
  • Continuous Air Monitor (CAM) Units
  • Purge Exhaust System
  • Toilet Exhaust System, and
  • Associated ductwork, dampers, instruments and controls.


What are the major components of the 'A' train of CRHVAC?

Air Handling Unit V‑95

Condensing Unit VC-11

Continuous Air Monitor Unit RIA-1818A

Charcoal Filter Unit VF-26A

Fan V-26A.


What are the major components of the 'B' train of CRHVAC?

  1. Air Handling Unit V‑96
  2. Condensing Unit VC-10
  3. Continuous Air Monitor Unit RIA-1818B
  4. Charcoal Filter Unit VF-26B
  5. V-26B.


How does Recirculation Mode for CRHVAC impact RIA-1818A/B's monitoring capability?

RIA-1818A/B are not located in the recirculation flow path thus will not detect adverse radiological conditions.


How does Recirculation Mode for CRHVAC impact pressure in the Control Room Envelope?

CRE will depressurize due to lack of makeup air.


How is Recirculation Mode initiated?

Initiated by placing DPIC-1659 (DPIC-1660) in manual and closing Damper D-2 (D-9).


What is the normal flow path for CRHVAC?

  1. Outside air is drawn in through a normal outside air intake
  • Tornado Damper TD-1 (TD-2)
  • Normal Air Intake Damper D-1 (D-8)
  • Modulating Damper D-2 (D-9)
  • Recirculation Damper D-3 (D-10) open, Recirculation Damper D-6 (D-13) closed
  1. Air discharges into Control Room Envelope
  2. Toilet Exhaust Fan V-16 discharges air through Exhaust Dampers D-17 & D-18 and Tornado Damper TD-6


What is the recirculation flow path?

  1. Modulating Damper D-2 (D-9) is closed
  2. Recirculation Damper D-3 (D-10) open
  3. Recirculation Damper D-6 (D-13) closed
  4. Air discharges into Control Room Envelope
  5. Toilet Exhaust Fan V-16 discharges air through Exhaust Dampers D-17 & D-18 and Tornado Damper TD-6


What is the flow path for purging?

  1. Purge Fan V-94 is started
  2. Purge Exhaust Dampers D-15 & D-16 open, Recirculation Damper D-3 (D-10) closes
  3. Control Room Differential Pressure Controller DPIC-1659 (DPIC-1660) modulates damper D-2 (D-9) as necessary to control pressure


What is the Emergency Flow Path?

  1. Verify Air Handling Unit V-95 (V-96) in service
  2. Air Filter Unit Fan V-26A (V-26B) in service
  3. Outside air is drawn in through emergency air intake through Tornado Damper TD-4 (TD-5) and Emergency Air Inlet Damper D-7 (D-14)
  4. Discharge Damper D-5 (D-12) opens
  5. VHX-26A (VHX-26B) heater energizes
  6. Dampers D-20 (D-21) modulate to control flow
  7. Normal Air Inlet Dampers D-1 & D-2 (D-8 & D-9) close
  8. Recirc Dampers D-3 & D-6 (D-10 & D-13) open
  9. Exhaust Fan V-16 trips if running, Dampers D-17 & D‑18, TD-6 close
  10. Purge Fan V-94 trips if running, Dampers D-15 & D‑16 close


How do CHP and CHR impact CRHVAC?

CHP (2 of 4 at 4 psig)

CHR (2 of 4 at 10R)

  • CRHVAC goes to Emergency
  • Condensing Units VC-11/VC-10 if operating will trip 


Explain why a positive pressure is maintained in the Control Room, Viewing Gallery, TSC, and Mechanical Equipment Room.

Prevents airborne radioactive material from entering the controlled area subsequent to accidents.

Differential Pressure Transmitter DPT-1659 (DPT-1660)

  • Compares Control Room pressure with South Corridor
  • Modulates damper D-2 (D-9) on the air inlet to maintain dp at 0.125” H2O



What is the design and operation of Air Handling Units V-95 (V-96)?

Each air handling unit consists of the following

  • A medium efficiency filter
    • Efficiency – 60 to 65%
  • An electric heating coil
    • Breaker open - not needed
    • MCC-77 (MCC-78)
  • A refrigerant cooling coil
    • 11,340 CFM of recirculated air and 1,160 CFM of outside air is cooled to 52°F prior to entering the Control Room envelope
  • A centrifugal fan
    • 12,500 CFM Centrifugal Fan
  • Associated ductwork, instrumentation and controls


What are the power supplies to V‑95/96?


  • V-95, Air Handling Unit, 'A' Train


  • V-96, Air Handling Unit 'B' Train


What is the function and power supply for VH-12/13, CRHVC Humidifiers?

  • HUC-1683 (HUC-1684) located in MER set at 40% ± 5%.
  • Rated 50 lb/hr, required 36 lb/hr
  • MCC-79 - VH-13
  • MCC-80 - VH-12
  • Not required to comply with Technical specifications


What makes up V-26A/B, Emergency Air Filtration Units?

Each Air Filtration Unit consists of the following components:

  • Fan V-26A (V-26B)
  • Prefilters VFP-26A (VFP-26B)
  • Electric Heating Coil VHX-26A (VHX-26B)
  • Upstream and downstream HEPA Filters VFH‑26A (VFH-26B)
  • Charcoal Filters VFC-26A (VFC-26B)
  • Associated ductwork, instrumentation and controls


What is the function of VF-26A/B's electric heater?

  • Electric Resistance Type 15 kW
  • Designed to reduce relative humidity of incoming air
  • Requires 12.48 kW
  • Ensures maximum charcoal filter efficiency
  • Power Supply – MCC-25 (MCC-26)
  • Minimum air flow for heater operation 2650 CFM


What is the purpose of the charcoal filters within the Emergency Air Filtration Units VF-26A (VF-26B)?

Minimizes exposure to radioactive materials during accident conditions

  • Two 2” beds in series (4” total charcoal depth)
  • Remove radioactive iodine



What detects fire in the charcoal beds?

Charcoal bed temperature can be monitored at Charcoal Filter Fire Alarm Panel

Dual meter indicates temperature for upstream and downstream charcoal beds.

  • Yellow “Detection High Alarm” indicating light illuminates at 220°F.
  • Red “Detection High-High Alarm” indicating light illuminates at 280°F.
  • Yellow “Detection Abnormal” indicating light illuminates when any of the following occur:
    • Open Sensor, terminator, or wiring.
    • Faulty or improperly seated status relay on the detection panel
    • Malfunction in the detection panel.


What is the design, capacity and power supplies for VF-26A/B, Emergency Handling Filter Fans? What starts them?

2 Stage Centrifugal Fan

  • Design flow 3200 CFM @ 10.0” H2O
    • 1000 CFM intake from outside air
    • 2200 CFM recirculated air
    • Driven by 20 Hp Motor

Power Supply

  • MCC-25 - VF-26A
  • MCC-26 - VF-26B

Automatically started by CHP/CHR


What is the power supply and design of VC-11 and VC-10?


  • VC-11


  • VC-10

Skid mounted 4-cylinder compressors with condensers

Capacity – 554,400 BTU/HR = 46.2 tons of refrigeration

60 Hp motor


How is VC-10/11 controlled?

Compressor loading/capacity is based on thermostats in the Control Room:

  • < 70ºF – Compressor will turn off.
  • 70ºF - 73ºF – One cylinder is loaded.
  • 73 ºF - 76 ºF – Two cylinders are loaded
  • > 76 ºF – All four cylinders are loaded


What is the function of the Hot Gas Bypass Valve, PCV-1675 (PCV‑1676)?

PCV-1675 (PCV‑1676)

  • Maintains a minimum compressor suction pressure under low cooling load conditions.
  • The lower coil is always in service.  This creates an artificial load that is sensed at the cooling coil outlet by the temperature controller.
  • This load causes the thermostatic expansion valve to open and inject more refrigerant into lower cooling coil, which maintains a minimum compressor suction pressure.
  • Hot Gas Bypass Mode will maintain suction pressure between 55 psig to 65 psig.


What provide the heat removal to VC-10/11 and how is it controlled?

Critical Service Water

  • VC-10 - 'A' Header
  • VC-11 - 'B' Header

CV-1655 (CV‑1656) controls based on shell side pressure of the condensing unit.

As load (air temperature) rises, shell side pressure rises, which opens the cooling water regulating valve and subsequently lowers the condenser temperature and pressure


What happens on a loss of instrument air, ac power, or dc power to VC-10/11?

Unit Trips

Low Suction Pressure when CV-1655/1666 fails open.

Upon loss of Instrument Air or DC Power to operating train, CRHVAC will fail to the RECIRC mode if in any mode other than emergency.


How do CHP and CHR interact with VC-10/11?

CHP/CHR shuts down Condensing Units

If cooling is required, control switch must be taken to CHP/CHR OVRD position.


What is the power supply and function of V-94, Purge Fan?

Power Supply – MCC-79

When operating in conjunction with the normal fan results in 8.4 air volume changes per hour.

Purpose is to evacuate smoke and/or noxious gas from the Control Room envelope.

Both Control Room AHUs must be available for the Purge Fan to start


How do CHP and CHR interact with the V-94, Purge Fan?

Purge Mode is blocked during Emergency Operation (CHP/CHR)

  • Unable to maintain Control Room pressure during purge

If running in Purge Mode, actuation of a CHP OR CHR will trip the Purge Fan


What interlocks are associated with V-94, Purge Fan?

Dampers D-15, D-16 and D-3 (D-10) are interlocked to the start of V-94

  • D-15 & D-16 OPEN, D-3 (D-10) CLOSE


How does outside air temperature, impact the Condensing Unit when placing the Control Room HVAC System in the Purge Mode?

Usually only a concern if the unit is out of service and the oil heater is not energized.

  • If operating in Purge Mode and outside air temperature is less than 70°F, compressor operation should be avoided.
  • Freon has an affinity for cold and could be absorbed in the oil and eventually condense into a liquid.
  • Upon starting of the unit damage could occur to the compressor.


What is the capcaity and interlocks associated with the toilet exhaust system?

  • Fan V-16 – 160 CFM
  • Isolation Dampers D-17, D-18, TD-6 open when fan is started
  • V-16 exhausts to roof by SIRW tank, opposite from RGEM
  • Control of V-16 is by a hand switch in restroom


How do CHP and CHR interact with the Toilet Exhaust System?

Trips on a CHP/CHR, OR start of either V‑26A/B Fan

  • Aligns system for Control Room pressurization


How do D-1, D-2, D-3, D-8, D-9, D-10, D-15, D-16, D-17, D-18 operate?

Air to operate

Spring return


What is the design function of D-1, D-2, D-8, D-9, D-15, D-16?

D-1, D-2, D-8, D-9, D-15, D-16 are “bubble tight” style dampers to reduce Control Room operator radiological whole body dose following a design basis accident (DBA)


What are the fail positions for Pneumatic Dampers?

Pneumatic Damper Fail Positions

  • Dampers D-1, D-2, D-8, D-9, D-15, D‑16, D-17, D-18 fail CLOSED
  • Dampers D-3, D-6, D-10, D-13 fail OPEN
  • Fail to Recirculation Mode lineup, unless in Emergency.


What are the power supplies and failure modes for D-7 and D-14?

D-7 Power Supply – 480 MCC-25

D-14 Power Supply – 480 MCC-26

Fail AS-IS on loss of power


What are the power supplies and failure modes for D-20 and D-21?

D-20 Power Supply – 480 MCC-25

D-21 Power Supply – 480 MCC-26

Fail OPEN on loss of power


What is the function of the tornado dampers?

Six tornado dampers installed in ductwork penetrating the Control Room envelope protect the Control Room from the depressurization effects of a tornado.

  • One in each normal air inlet (2)
  • One in each emergency air inlet (2)
  • One in Purge Exhaust Duct
  • One in Toilet Exhaust Duct

Close on reverse air flow


How do and what is the function of fire dampers?

Fire Dampers are installed in various supply and return ducting.

  • Three hour fire rated dampers (Fire Barriers)
  • Operate by melting a fusible link at 165°F
    • Damper CD-49 (CD-51) fusible link has been replaced with a higher temperature fusible link (212°F) due to location in duct
    • Link is located just downstream of the steam distributor for the humidifier


What are the operating requirements for Continuous Air Monitors (CAM) RIA-1818A/B?

Not Saftey Related, No Automatic Functions

Operation of a CRHVAC train with a CAM out of service is only allowed in the emergency mode per SOP-24.


Why is there an OFF/RESET position for V-96/96 Control Switch?


  • AHUs receive a trip signal during load shed.
  • When the sequencer (either Shutdown or DBA) sends a start signal to the AHU, the load shed trip is cleared.
  • On sequencer failure, the load shed trip is locked in and the AHU wil not start in either AUTO or ON

Resets the Load Shed circuitry and allows starting of the AHU.



What equipment is in operation during 'A' Train in service Recirculation Mode?

D-1, 2, 3, 17 and 18 are Open. D-2 is Closed.

Cannot maintain positive pressure.

  • -D-6, 7, 15, and 16 are closed
  • -V-95 in service with VC-11 cooling
  • -V-16 in service
  • RIA’s not in the flow path therefore will not detect adverse radiological conditions
  • -Need SM or SED permission to go to Recirc Mode


How does CHP/CHR and Load Shed impact V-95/96 with the Control Switch in Auto?

Load shed and Sequencer (NSD or DBA) circuitry places the Air Handling Units in the same condition they were in before the loss of power 55 seconds after the bus is re-energized.

If in AUTO and CHP/CHR

  • V-95/96 will start after a 1 minute time delay 


Which fans can be controlled locally?

V-95 (V-96)

V-26A (V-26B)

Purge Fan V-94


Identify redundant Control Room indications that can be used to validate Control Room alarm:

•           EK-0249 CONTROL ROOM LOW PRESS DPIC-1659/1660

Check DPIC controller indication

  • Located on back of C-11A at knee level

Check Control Room Envelope doors properly closed

Other parameters external to the Control Room can be checked for additional trouble shooting such a normal and emergency air intakes clear.


How do the following systems interact with CRHVAC?

  • Service Water
  • Municipal Water
  • Instrument Air
  • Dirty Radwaste
  • Fire Protection
  • Turbine Sump
  • Electrical Power

  • Service Water
    • Critical Headers supply VC-10/11 condensors
  • Municipal Water
    • Provides Humidifier Steam Tank with water
  • Instrument Air
    • Operates Dampers/Condensor TCV, etc
  • Dirty Radwaste
    • Charcoal Filters drain here after fire 
  • Fire Protection
    • Manual deluge/flooding connection for charcoal filter
  • Turbine Sump
    • Humidifier drains here
  • Electrical Power
    • Various sources


Loss of panel D-11A will cause what to happen?

Left train of CRHVAC to fail to the emergency mode regardless of status of operation.

VC-11 trips and will not restart.


What happens on a loss of D-21A?

Right train of CRHVAC to fail to the emergency mode regardless of status of operation.

VC-10 trips and will not restart.


What happens on a loss of Preferred AC Bus Y‑10 ?

Left train cannot be operated in emergency mode

If left train is in operation, it will fail to recirculation mode

VC-11 trips and will not restart


What happens on a loss of Preferred AC Bus Y‑20?

Right train cannot be operated in emergency mode

If Right train is in operation, it will fail to recirculation mode

VC-10 trips and will not restart


What trips VC-10/11?

- High Discharge Pressure
-Low Suction Pressure
-Low Differential Oil Pressure
-High Oil Temperature


How does Cable Spreading Room ventilation interact with CRHVAC?

When CRHVAC is operated in Emergency Mode then, Switch Gear Exhaust Fan, V-47, SHALL not be operated


How do RIA 1818A/1818B interact with CRHVAC?

Emergency Mode should be manual initiated within 20 minutes of actuation of Rad
Monitor, RIA 1818A/1818B


How is EDG Loading managed with CHP/CHR and CRHVAC?

During CHP/CHR if Control Room Temperature is <110F then VC-10/11 may be
off to minimize EDG loading.