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NLO Systems 2023 > GA- Service gases (Nitrogen and Hydrogen) > Flashcards

GA- Service gases (Nitrogen and Hydrogen) Flashcards

1
Q

What is the purpose of the GA Hydrogen System?

A

Provides hydrogen gas for cooling the Main Generator at 75 psig and provides VCT overpressure (oxygen scavenging from the CVCS) at 15-20 psig

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2
Q

How many hydrogen storage banks are there in the GA system?

A

Two (7 cylinders per bank)

one bank is active and the other bank is reserve

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3
Q

How does the Grounding System (QG) support the GA Hydrogen system?

A

Provides safety grounding to prevent ignition sources, personnel and equipment safety for the hydrogen system

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4
Q

What is the capacity of the GA Hydrogen Gas Storage Cylinders based on?

A

Provides two complete charges of the main generator plus 30 days consumption for generator cooling and reactor coolant system oxygen scavenging

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5
Q

What is the GA hydrogen system pressure maintained at?

A

2300 – 200 psig

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6
Q

At what pressure do we receive an alarm in the Control Room regarding the GA hydrogen system?

A

200 psig

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7
Q

Where is the GA Hydrogen Storage system located? Is the hydrogen system required for safe shutdown?

A

North of the Turbine Building

no

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8
Q

What is used to shut-off gas flow in the event of a line rupture in the GA hydrogen system? When will the excess flow valve be able to reopen?

A

Excess flow valve on the excess flow manifold, set at 30,000 scfh

when the differential pressure across the valve is zero (using the excess flow bypass to relieve pressure)

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9
Q

What impact would a loss of the GA hydrogen system have on the plant?

A

VCT could lose its cover gas which could prevent oxygen scavenging in the RCS and create chemistry concerns

Main generator may have to be shutdown or be operated at a reduced loading

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10
Q

The GA Nitrogen System provides nitrogen blanketing to what components with low pressure nitrogen?

A

TC, NC, EW, EC, WC surge tanks

CST, DWST, EDT, RDT, SITs, VCT for cover gas

Steam Generators

BAC

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11
Q

The GA Nitrogen System pressurizes what plant components with high pressure nitrogen?

A

SITs, ADVs, Steam Generator Downcomer Feedwater Isolation and Control Valve Accumulators

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12
Q

The GA Nitrogen System is used to purge what components with low pressure nitrogen?

A

CVCS Gas Stripper, Feedwater heaters, GR system, LRS Evaporator, Pressurizer, VCT, EDT, and RDT

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13
Q

The GA Nitrogen System is used to maintain chemistry of what components with low pressure nitrogen?

A

Main condenser, LRS BAC vent cooler

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14
Q

Where are the main components of the GA Nitrogen System located?

A

Northwest yard, plant east of the ‘A’ spray pond

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15
Q

What pressure is the Low Pressure Nitrogen maintained at?

A

115 psig (105 psig backup)

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16
Q

What pressure is the High Pressure Nitrogen maintained at in the active banks? Reserve banks?

A

650 psig

630 psig

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17
Q

What powers the Nitrogen Control Panel and Liquid Nitrogen Pumps?

A

NH

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18
Q

What powers the containment isolation valves in the GA nitrogen system? When do they close?

A

PK

CIAS or LOP

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19
Q

At what IA pressure will the LP Nitrogen system be supplied to its header?

A

85 psig

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20
Q

The IA system receives LP nitrogen as a backup to what components normally supplied by instrument air?

A

To operate the SG Downcomer Control Valves actuators

To open SG Downcomer Isolation Valves

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21
Q

At what pressure is Nitrogen supplied to provide the motive force to open the FW Downcomer Isolation valves?

A

240 psig

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22
Q

What is the capacity of the Nitrogen Storage Tank and what is the design of the tank?

A

3082 gallons at a design pressure of 245 psig

double walled, liquid inside the inner wall and a vacuum with insulation between the walls

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23
Q

How often is the Nitrogen storage tank refilled? How is it filled?

A

Twice per week while at power, or as needed during an outage

through the top fill valve or the bottom fill valve

driver performs all operations with the supervision of the AO

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24
Q

How full do we fill the Nitrogen storage tank to?

A

~85%

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25
Q

What pressure do we maintain in the Nitrogen storage tank?

A

150 – 160 psig

26
Q

What happens if pressure drops below 150 psig in the nitrogen storage tank?

A

A Nitrogen Tank Pressure Buildup Regulator opens and nitrogen is vaporized in the pressure buildup coil and returned to the top of the nitrogen tank to maintain tank pressure at 150 psig

27
Q

What happens if pressure rises above 160 psig in the nitrogen storage tank?

A

A Tank Vapor Space Backpressure Control Valve opens which bleeds gas from the top of the tank to the liquid supply line for the low pressure vaporizer, lowering tank pressure

28
Q

When would the nitrogen storage tank’s safety relief valve lift? What other overpressure protection is there?

A

245 psig

Also has a rupture disc

29
Q

What is the administrative maximum pressure of the nitrogen storage tank?

A

220 psig

30
Q

What is the purpose of the Liquid nitrogen pumps? What is the capacity of the Liquid Nitrogen pumps?

A

provide motive force to transfer the contents of the liquid nitrogen storage tank to the high pressure nitrogen storage banks for use in the HP nitrogen system

14,000 scfh

31
Q

How would I know which Liquid Nitrogen pump is the non-selected pump?

A

Associated disconnect would be open

32
Q

At what pressure in the Nitrogen system Active Bank will the Standby pump start?

A

1400 psig

33
Q

What happens after the switch for the liquid nitrogen pump is taken to START?

A

Pump running light and the ‘COOLDOWN LIGHT’ will illuminate, pump inlet and vapor return valves will open

After 15 minutes, the pump ‘COOLDOWN’ light will turn off and the pump will start

15 seconds after the pump starts, the vapor return solenoid valve will shut

34
Q

How long will a Liquid Nitrogen pump run for?

A

Until the Active Bank reaches 2100 psig

35
Q

What conditions would stop the Liquid Nitrogen pumps? Basis?

A

Low temperature downstream of the high pressure vaporizer -> prevents liquid carryover into the nitrogen cylinders

High pump discharge pressure at 2400 psig -> prevents lifting of safety relief valves and protects the system from overpressure

Liquid nitrogen storage tank low level at 25” -> prevents pump damage from low suction pressure

36
Q

What is the purpose of the Nitrogen Vaporizers?

A

Low pressure vaporizer transforms the liquid nitrogen from the storage tank to a low pressure gas for use in the low pressure nitrogen header

High pressure vaporizer transforms the liquid nitrogen pump discharge flow into a gas for storage in the high pressure nitrogen gas storage banks

37
Q

What is the purpose of the Nitrogen Gas Storage Cylinders?

A

Provides storage of high pressure nitrogen utilized in the system

Gas capacity is sized for a 7 day normal usage demand

38
Q

What does the Nitrogen Gas Storage Cylinders consist of?

A

Two banks of four cylinders which are isolated from each other by a closed valve

(active bank and reserve bank)

39
Q

What low pressure in the Nitrogen Gas Storage Cylinders would cause an alarm in the Control Room? Where else can the cylinders be charged from?

A

750 psig in either bank

trailer truck

40
Q

What is the nitrogen pressure alarm setpoint of the ADV? What is the high setpoint?

A

635 psig

700 psig

41
Q

What could happen if we lost High Pressure Nitrogen?

A

If lost for an extended period of time, then ADV accumulator pressures would fall below 615 psig and affect the required 16 hour coping time requirement for heat removal during a Station Blackout

42
Q

What is the flowpath of the GA hydrogen system?

A

Active and reserve banks are normally aligned to their respective pressure control valves, then downstream of the PCVs the two headers combine into one common header, then to an excess flow control valve and on to the system loads

43
Q

In the GA hydrogen system, when is the active bank isolated, the cross-connect opened and the reserve bank feeds both pressure control valves?

A

when active bank pressure lowers to ~300 psig

44
Q

In the Hydrogen system, what pressure is the system reduced to down stream of the Pressure Control Valves?

A

100

PCV-15 is ~105 and PCV-16 is ~95 at their outlets

45
Q

Describe some hydrogen characteristics and safety precautions.

A
  • colorless, odorless gas
  • burns with invisible flame
  • flammable with air mixture 4-74.2%
  • explosive air mixture 8.2-58.9%
  • heats up during rapid expansion
  • spark or ignition source is not required to start a hydrogen fire or explosion
  • no smoking in the area
  • no ignition sources within 25ft
  • no combustion sources within 50 feet
  • non-sparking tools only
  • no excessive torque on valves or regulators (potential hydrogen release)
  • control and monitor venting hydrogen gas
46
Q

What are the main components of the nitrogen gas system?

A
  • Liquid nitrogen storage tank
  • two liquid nitrogen pumps
  • LP nitrogen vaporizer
  • HP nitrogen vaporizer
  • nitrogen gas storage cylinders
  • regulating valves
47
Q

What is the flow path of the Nitrogen system?

A

from storage tank:

LP- low pressure ambient vaporizer, then through the normal or backup pressure control valve/pressure regulating valve to supply the low pressure header loads at 115 (normal) or at 105 (backup)

HP- liquid nitrogen pumps take suction on the storage tank and go through a high pressure ambient vaporizer to the active and reserve storage banks, then to the PCV/PRV to maintain the nitrogen header at 650 (normal) or 630 (backup)

48
Q

Why is LP nitrogen sent to the condenser at power?

A

to control condensate dissolved oxygen

49
Q

When do the steam generators receive LP nitrogen?

A

wet layup conditions

50
Q

When does the RCS receive HP nitrogen?

A

to the pressurizer during depressurization and cooldown

51
Q

When does the RDT, EDT, and the VCT receive LP nitrogen?

A

while shutdown

52
Q

When does the BAC receive LP nitrogen?

A

as cover gas while shutdown

chemistry control while at power

53
Q

What is the difference between using the top fill valve and the bottom fill valve to off load nitrogen into the Nitrogen storage tank?

A

bottom fill valve will increase level and tank pressure

top fill valve will increase tank level while decreasing pressure (due to top valve directing flow through a spray head that condenses some of the vapor as the liquid falls to the liquid level)

54
Q

What is the purpose of the Liquid nitrogen control panel? What does it monitor? How is the PLC cooled?

A

provides controls, indications and alarms for the high pressure liquid nitrogen pumps and their associated solenoid valves

  • HP nitrogen active bank pressure
  • liquid nitrogen storage tank level
  • HP nitrogen header temperature downstream of the vaporizer

a small portion of low pressure nitrogen is routed through a PCV to the control panel

55
Q

Where is the nitrogen skid located?

A

north yard, just east of the A spray pond

56
Q

What alarms are associated with the Nitrogen system?

A

high pressure in the active bank

low temp. in the high pressure header downstream of the vaporizer

low level in the storage tank

57
Q

What is the purpose of the Liquid nitrogen pump override push button and override light?

A

if active bank pressure is between 1400 and 2100 and you want to run the pump, you push the button, the light will come on and then you press the start button

then the pump will raise pressure to 2100 psig

58
Q

How do the low and high pressure nitrogen vaporizers work?

A

they are HXs that absorb the heat from the surrounding air

the HX tubes are finned and in series for maximum surface area contact

low pressure nitrogen is directed to the LP nitrogen header and HP is directed to the storage banks

59
Q

What happens when the LP nitrogen header is lost?

A

HP nitrogen system will supply the LP side at 100 psig through a PCV

60
Q

What happens when we lose LP nitrogen? HP nitrogen?

A

surge tank cover gases are lost and if IA is lost too, plant would shutdown

ADVs would eventually inop and affect the 16hr coping time

NLO Systems 2023 (67 decks)

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