Service Gasses (GA) (N2, H2)

Question 1

What is the purpose of the N2 system?

Answer 1

Vaporizes liquid nitrogen to supply both high and low pressure gas headers

N2 blanket:
TC, NC, EW, EC, WC Surge Tanks
CST, DWST, RDT, EDT, Condenser hotwell, and VCT (outage), SITs

Provide N2 to:
Ø SG Downcomer Control and Isolation valves
Ø back up to instrument air
Ø Blanketing of SG’s, BAC, and LRS Evap
Ø Purge Gas stripper
Ø Purge FW heaters during outage and post outage
Ø Purge GR system header for a High O2 condition
Ø Post accident sampling system (PASS)

Question 2

What is normal N2 storage tank pressure?

How is the tank filled?

Answer 2

Normal pressure is at 150 psig

Fill either via top or bottom valve
Normally from bottom, but use top to lower pressure

Question 3

What kind of pumps are the N2 pumps?

Answer 3

reciprocating, positive displacement

Question 4

What is the power supply and alignment of the N2 pumps?

Answer 4

NH

Power supply disconnect switch is closed for in-service pump, the other pumps switch is usually open.

Question 5

At what pressure in the N2 storage banks does the selected N2 pump start and stop?

Answer 5

Start @ 1400 psig on active bank

Stop @ 2100 psig on active bank

Question 6

What will automatically stop the N2 pumps?

Answer 6

Hi pump discharge pressure (2400 psig) (prevent lifting reliefs and protect pump)

High Pressure Nitrogen Vapor temp decreasing -20 degrees F (prevent liquid Nitrogen going to cylinders)

Active nitrogen storage bank decreasing 10 degrees F

Liquid nitrogen storage tank at 25” ( prevent pump damage from lower suction pressure, cavitation)

Question 7

What happens directly after the N2 pumps get a start signal?

Answer 7

15 minute cooldown cycle by allowing liquid nitrogen to flow into the pump

Question 8

At what pressure is the N2 low pressure header maintained normally?

How is the header supplied?

Answer 8

~115 psig by PCV-0049

from tank to the vaporizer and right onto the header

Question 9

At what pressure is the high pressure N2 header maintained normally?

How is the header supplied?

Answer 9

~650 psig

from tank through liquid N2 pumps to the high pressure vaporizer and then to the active and reserve banks. from the banks to the header

Question 10

What are the N2 storage banks sized for?

Answer 10

Sized for 7 day normal usage demand. The total usable storage capacity is evenly divided into two banks of four cylinders each, one active and the other reserve.

Question 11

When do the N2 outside containment isolation valves, GAA-UV1/UV2, close automatically?

Answer 11

CIAS

loss of PKA

Question 12

What do N2 outside containment isolation valves, GAA-UV1/UV2, provide nitrogen to?

Answer 12

UV1 - HP N2 to SITs

UV2 - LP N2 to RDT

Question 13

What does the H2 header supply?

Answer 13

VCT when online

Main generator

Question 14

What is the purpose of H2 in the main generator?

what needs to happen if hydrogen is reduced in the generator?

Answer 14

cooling

reduce generator loading

Question 15

What is the purpose of H2 in the VCT?

what will happen if hydrogen is reduced in the VCT?

Answer 15

oxygen scavenging

increased corrosion in CH system

Question 16

When does the CR get an alarm for low H2 storage bank pressure?

When do we normally swap to the reserve bank?

Answer 16

200 psig in active bank

300 psig

Question 17

What component is in place that prevents dumping H2 when there is a line break downstream of the H2 farm?

how is this component reset?

Answer 17

excess flow check valve (excess flow manifold)

bypass opened to equalize pressure across the valve

Question 18

What could bring in this alarm?

Answer 18

Causes for this annunciator include:
* Nitrogen or Hydrogen active or reserve bank pressures Lo
* Nitrogen Control panel Trouble
* Hydrogen, low pressure Nitrogen, or high pressure Nitrogen header
pressures Hi

Question 19

What could bring in this alarm?

Answer 19

Causes for this annunciator include:
* Instrument Air valve opens on IA low pressure to supply IA header
from N2 low pressure system