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Catawba Nuclear Station > Waste Gas System(WG) > Flashcards

Waste Gas System(WG) Flashcards

1
Q

What is the purpose of the Waste Gas System?

A
  1. Collect fission gases, store them until activity decays to levels acceptable for release
  2. Controlled, monitored release of stored radioactive gas to environment
  3. Reduction in fission gas concentration in the NC system which reduces the escape of gases during maintenance or through leaks
  4. Remove air, hydrogen, and fission gases from NC system and associated components during degas
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2
Q

What is the system designator for the Waste Gas System?

A

WG

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3
Q

What are the components that make up the Waste Gas System?

A
  1. 2 compressors
  2. 2 hydrogen recombiners
  3. 8 waste gas decay tanks:
    A. Three banks
    B. 2 banks of three for normal service
    C. 3rd bank is for shutdown
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4
Q

Where does the Waste Gas System receive gas from?

A
  1. Mixed fission/hydrogen gas purge from the VCT
  2. Recycle and waste evaporators
  3. Degasification of the NC system(NCDT, PRT, PZR)
  4. Gases from under the diaphragms of the RHT and WDT
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5
Q

How are the Normal Waste Gas Decay Tanks divided into banks?

A

1st bank - A, B, and C WGDTs

2nd bank - D, E, and F WGDTs

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6
Q

Which Waste Gas Decay Tank do all releases come from?

A

The ‘C’ Waste Gas Decay Tank

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7
Q

What is the relief pressure for all of the normal Waste Gas Decay Tanks?

A

150psig

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8
Q

Where do all of the reliefs for the Waste Gas Decay Tanks relieve to?

A

The Waste Gas Decay Tanks all relieve to the ‘A’ Shutdown Waste Gas Decay Tank(SWGDT)

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9
Q

How many Shutdown Waste Gas Decay Tanks are there?

A

There are two Waste Gas Decay Tanks in the 3rd or Shutdown bank

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10
Q

What is the purpose of the A Shutdown Waste Gas Decay Tank?

A

The ‘A’ Shutdown Waste Gas Decay Tank receives relief gases from the normal Waste Gas Decay Tanks

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11
Q

What pressure is maintained in the ‘A’ Shutdown Waste Gas Decay Tank?

A

Pressure is maintained less than 5psig

Shutdown Waste Gas Decay Tank ‘A’ is never placed in service

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12
Q

What is the purpose of the ‘B’ Shutdown Waste Gas Decay Tank?

A

Shutdown Waste Gas Decay Tank ‘B’ is used to store nitrogen for shutdown

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13
Q

What are the relief setpoints for the Shutdown Waste Gas Decay Tanks, and where is that relief gas directed?

A

A - 100psig
B - 150psig

Directed to the Unit Vent

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14
Q

Where are the Waste Gas Decay Tank Drains directed to?

A
  1. RHT, but this is administratively controlled

2. Normally pumped to the Waste Evaporator Feed Tank Sump B

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15
Q

Where are the Waste Gas Hydrogen Recombiner and Compressor drains directed to?

A

Waste Evaporator Feed Tank Sump B

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16
Q

What prevents gases from being drained along with the liquid from the Waste Gas System components?

A

All of the drains have a gas trap to prevent gases from being drained with the effluent

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17
Q

What are the components that make up a Waste Gas Hydrogen Recombiner?

A
  1. Preheater
  2. Catalytic Reactor Assembly
  3. Cooler
  4. Phase Separator
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18
Q

How does the Instrument Air System interface with the Waste Gas Hydrogen Recombiners?

A

Instrument air is used for the valve actuators to allow oxygen admission

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19
Q

How does the Component Cooling System interface with the Waste Gas Hydrogen Recombiners?

A

Component cooling water provides a heat sink for the cooler

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20
Q

What is the purpose of the Inlet Pressure Control Valve associated with the Recombiners?

A

Controls the pressure in the recombiner at 30psig plus or minus 5psig

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21
Q

What is the purpose of the Preheater?

A

Immersion style electric heater used to preheat the feed gas prior to entering the catalytic reactor to the initial reaction temperature

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22
Q

What is the purpose of the Oxygen Addition Valves?

A
  1. Controls the amount of oxygen added to the catalytic hydrogen recombiner(one per recombiner)
  2. Can be controlled in manual or automatic
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23
Q

What is the purpose of the Waste Gas Hydrogen Recombiner?

A

Combines hydrogen and oxygen to form water(steam at the outlet)

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24
Q

What is the purpose of the Waste Gas Heat Exchanger, and what is the cooling medium?

A
  1. The Heat Exchangers condenses the steam leaving the recombiner
  2. Component cooling provides the cooling medium for the heat exchanger
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25
Q

What is the purpose of the Waste Gas Phase Separator?

A

Removes water droplets from the gas/water vapor mixture leaving the heat exchanger using a swirling action. The water drops to the bottom and the gas leaves the top

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26
Q

How is the water level maintained in the Waste Gas Phase Separator?

A

Level is controlled by an automatic drain valve that directs drainage to Waste Evaporator Feed Tank Sump B

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27
Q

How often are the Hydrogen Recombiners swapped?

A

Quarterly

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28
Q

What is the oxygen/hydrogen precaution associated with Waste Gas Operation?

A

Oxygen and hydrogen are monitored and controlled such that system oxygen is less than or equal to 2% whenever hydrogen is greater than 4%

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29
Q

What are the pressure and flow values to ensure proper operation of the Hydrogen Recombiner?

A
  1. Pressure should be maintained greater than or equal to 30psig
  2. Flow should be maintained greater than or equal to 1800scfh to prevent flame propagation
30
Q

What are the power supplies to the Waste Gas Compressors?

A

A - SMXA

B - SMXB

31
Q

What components make up the Waste Gas Compressor Package?

A
  1. Compressor
  2. Separator
  3. Heat Exchanger
32
Q

How does the Instrument Air System interface with the Waste Gas Compressor Package?

A

Provides air for valve operators

33
Q

How does the Component Cooling System interface with the Waste Gas Compressor Package?

A

Component Cooling supplies the cooling medium to the heat exchanger

34
Q

How does the Reactor Makeup Water System interface with the Waste Gas Compressor Package?

A

Provides makeup water to the separator as needed

35
Q

What is the purpose of the Waste Gas Compressor?

A
  1. Provides the motive force for moving gases within the WG system
  2. Compressor maintains continuous circulation of gases around(within) the waste gas loop
36
Q

What is the purpose of the Moisture Separator?

A

The moisture separator allows separation of the gases and water exiting the compressor.

37
Q

How does the Moisture Separator separate the liquid and gas?

A
  1. Increase in size as the mixture transitions from the pipe to the separator allow for a decrease in velocity. The heavier water drops out of the mixture.
  2. Centrifugal force is also used to separate the liquid and gas
38
Q

What provides the cooling medium to the Compressor Heat Exchanger?

A

Component Cooling provides the cooling to the Compressor Heat Exchanger for removal of heat from the seal water

39
Q

What is the purpose of the Waste Gas Analyzers, and how many are there?

A
  1. There are 2 Gas Analyzer Racks(GAR) which monitor the system for hydrogen and oxygen to:
    A. Verify explosive mixtures are not present
    B. Provide appropriate alarms and trip functions
    C. Each GAR can only be placed in service with the associated Catalytic Hydrogen Recombiner(CHR)
40
Q

What types of analyzers are used in the Waste Gas System?

A
  1. Orbisphere hydrogen/oxygen analyzers

2. Oxygen analyzers

41
Q

How does the Hydrogen Orbisphere measure hydrogen concentration?

A
  1. Uses a semipermeable membrane and a gas thermal conductivity sensor.
  2. Hydrogen passes through the membrane and is detected by the thermal conductivity sensor
42
Q

How does the Oxygen Orbisphere measure oxygen concentration?

A
  1. Uses a semipermeable membrane and cathode to detect oxygen
  2. The oxygen passes through the membrane and reacts with the cathode. This reaction produces and electrical signal proportional to oxygen concentration
43
Q

How can water buildup be detected in the Waste Gas Analyzers?

A

Water build up can be observed in the drain tank sight glass on the Orbisphere analyzers

44
Q

What can excess water in the Waste Gas Analyzers lead to?

A
  1. Increase in filter D/P requiring increased filter change outs
  2. Erratic hydrogen/oxygen readings
  3. Problems with flow measurement instrumentation
45
Q

How do the System Oxygen Analyzers detect oxygen concentration?

A
  1. System oxygen analyzers detect oxygen electrochemically through the use of a micro-fuel cell, a type of galvanic cell.
  2. Oxygen will pass through a membrane and be dissolved in an electrolyte solution. The oxygen will migrate to a sensing electrode and current produced will be proportional to oxygen concentration
46
Q

How can water build up be detected in the System Oxygen Analyzers?

A

Water will build up will be observable in the rotometers of the analyzers

47
Q

What can excess water in the System Oxygen Analyzers lead to?

A
  1. Fuel cell failure
  2. Incorrect oxygen readings
  3. Flow rotometers to stick
48
Q

What is the largest source of input to the Waste Gas System, and how does it enter the system?

A
  1. The largest source of gas in the Waste Gas System is from the Volume Control Tank(VCT)
  2. Fission product gases are removed from NC via VCT purge.
  3. Fission product gases are removed and replaced as hydrogen will automatically makeup to the VCT as pressure lowers
49
Q

How is gas transferred from the Reactor Coolant Drain Tank to the Waste Gas System?

A

The NCDT has a nitrogen or hydrogen overpressure during operation. When pressure in the NCDT rises gases will be vented to the Waste Gas System

50
Q

How is gas transferred from the Pressurizer Relief Tank to the Waste Gas System?

A
  1. The PRT has a nitrogen overpressure on it during normal operations.
  2. Gas from the PRT is transferred to the Waste Gas System when:
    A. Pressure needs to be lowered
    B. Gas space needs to be purged
    C. Chemistry needs to sample the PRT gas space
51
Q

How is gas transferred from the Recycle Evaporator Vent Condenser to the Waste Gas System?

A

Gases stripped from the feed liquid can vent to the Waste Gas System or the Unit Vent which is preferred to prevent excessive moisture carryover in the Waste Gas System

52
Q

How is gas from the Volume Control Tank Sample Space transferred to the Waste Gas System?

A

Purging of the sample lines is necessary to obtain samples so that purge volume will be transferred to the Waste Gas System

53
Q

How is gas transferred from the Recycle Holdup Tank and the Waste Drain Tank to the Waste Gas System?

A

There is a diaphragm that separates the liquid in the tank from the atmosphere. Periodically it is necessary to remove gases that come out of solution from under the diaphragm to prevent explosive mixtures. These gases are sent to the Waste Gas System.

54
Q

What will cause the Waste Gas Discharge Flow Control Valve(1WG-160) to automatically close?

A

The WG Discharge Flow Control Valve will close on a Trip 2 signal from:

  1. WG discharge monitor 0EMF-50
  2. Unit Vent gaseous monitor 1EMF-36
  3. Unit Vent particulate monitor 1EMF-35
55
Q

What is the interlock associate with Compensated Seal Water Valves?

A

At 5 psid decreasing the compensated seal water valves open to prevent compressor stall at higher pressures

56
Q

What is the interlock associated with the Compressor Unloader Valve Relief?

A

At 100psig solenoid valve is de-energized to open separator gas unloader valve to prevent a compressor stall

57
Q

What will cause a Waste Gas Compressor to trip?

A
  1. High moisture separator level or pressure
  2. Low moisture separator level or pressure
  3. Low suction pressure
58
Q

What types of trips do the Catalytic Hydrogen Recombiners have?

A
  1. Fast Trips(vents control air)

2. Slow Trips(bleeds control air)

59
Q

What does a trip of the Catalytic Hydrogen Recombiner accomplish?

A

Trips, either fast or slow, cause the oxygen supply valve to close

60
Q

What affect does a “Fast Trip” have on the Oxygen Addition Valves?

A

The Oxygen Addition valves are air actuated valves. When a fast trip occurs the air is vented from the air actuator causing the valves to close

61
Q

What additional signal is generated by a “Fast Trip” signal in the Waste Gas System?

A

The VCT purge outlet isolation valves will trip if BOTH oxygen addition valves have an active “Fast Trip Signal”

62
Q

How many valves close on “Fast Trip” signal?

A

All four valves should close:
2 VCT purge valves
2 Oxygen addition valves

63
Q

What are the Recombiner “Fast Trip” signals?

A
  1. 900 ppm oxygen outlet(200 second time delay)
  2. 950F outlet of CHR
  3. 200F outlet of heat exchanger
  4. 350F oxygen addition point
  5. Less than 1800 scfh flow
  6. 9% inlet hydrogen
  7. 3% inlet oxygen
  8. Pressing the “Emergency Close” pushbutton
64
Q

What will cause a “Slow Trip” of the Recombiners?

A

A high temperature slow trip signal is generated when thermocouples inside the CHR reach 1050F

65
Q

What affect does a “Slow Trip” have on the Oxygen Addition Valves?

A
  1. The slow trip was originally designed to give the recombiner a chance to recover
  2. The air for the oxygen addition valve actuator is slowly bled off through an adjustable orifice cause the valves to slowly close
66
Q

What will cause the VCT Purge Outlet Isolation Valves to automatically close, and the purpose?

A
  1. Low VCT pressure
  2. Low Waste Gas Compressor Suction Header Pressure(0.5psig)
  3. Both Recombiner oxygen addition valves “Fast Trip” signals

These interlocks prevent gas binding of the NV pumps and ensures adequate backpressure to the NCP seals

67
Q

What are the two modes of operation for the Waste Gas System, and what mode do we use?

A
  1. The two modes of operation are:
    A. High Pressure Mode
    B. Low Pressure Mode
  2. CNS uses the High Pressure Mode only
68
Q

What is the basic flow path of the High Pressure Mode of operation?

A

Compressor—>WGDT—>Recombiner

gas is then sent back to the suction of the compressor at approximately 0.5psig

69
Q

What different types of Volume Control Tank Purge is there?

A

The VCT can be run on either a continuous purge or intermittent purge to maintain fresh hydrogen concentration in the VCT

70
Q

How many Waste Gas Decay Tanks are in service at a time?

A

Only one WGDT is placed in service at a time, and are typically left in service until the CHR flow rate cannot be maintained due to tank filling.

71
Q

What gases are used in the Volume Control Tank, and when?

A
  1. Shutdown uses nitrogen

2. Normal operation uses hydrogen

72
Q

Why would we need to perform a nitrogen purge of the VCT prior to startup?

A

The oxygen concentration in the VCT may need to be lowered(less than 3%) prior to admitting hydrogen

Catawba Nuclear Station (72 decks)

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