Service Gases- Hydrogen

Question 1

What is hydrogen service gas used for ?

Answer 1

-Cooling main generator
Maintained at 75psig
-Volume Control Tank (VCT) over pressure
Pressure maintained at 15-25psig for the purpose of oxygen scavenging in RCS

Question 2

What is flow path for hydrogen system ?

Answer 2

-Two storage banks of 7cylinders each(Active/Reserve)
-Normally aligned to there respective pressure control valve
- After the PCVS they come together in a common header
-Hydrogen then flows through Excess Flow Control valve to loads:
VCT & Main Generator

Question 3

What happens when active bank lowers to 300 psig?

Answer 3

-Active bank is isolated and then active/reserve cross connect valve is opened to align reserve bank to both active and reserve PCVs

Question 4

How does Hydrogen system interface with Ground system (QG) ?

Answer 4

Provides safety grounding to prevent ignition sources

Question 5

How does Hydrogen system interface with Generator Hydrogen and CO2 system (GH) ?

Answer 5

GH system receives hydrogen gas for main generator cooling

Question 6

How does Hydrogen system interface with Chemical& Volume Control system(CH) ?

Answer 6

CH system receives hydrogen gas for used for RCS oxygen scavenging

Question 7

What is the purpose for Hydrogen Gas Storage Cylinders?

Answer 7

-Hydrogen storage banks provide two complete charges of main generator
-Also provides 30 day generator cooling and RCS oxygen scavenging

Question 8

What’re cylinder in each bank connected to ?

Answer 8

Connected to pigtails on manifold with isolation valve and rupture disc for each cylinder

Question 9

What is each manifold provided with ?

Answer 9

-Isolation Valves
-Relief valves
-Pressure indications
-Temperature Indications

Question 10

What is the storage bank pressure maintained at ?

Answer 10

-Maintained between 2300psig-200psig
-Bank is isolated when it reaches 300psig

Question 11

What pressure will control room receive an alarm at ?

Answer 11

-When active bank reservoir is at 200psig
-Once pressure is below 200psig chemistry has to be involved for hydrogen purity reasons

Question 12

What do the Pressure Control Valves do for the hydrogen system ?

Answer 12

-It reduces hydrogen pressure from approximately 2300psig-100psig

Question 13

What is the excess flow manifold/excess flow valve designed to do ?

Answer 13

-Designed to close on excess flow (30000 SCFH) hydrogen flow
-Supposed to be bubble tight and not reopen until DP across valve is reduced to zero

Question 14

What’re hydrogen characteristics ?

Answer 14

-Colorless,odorless gas
-Burns with an almost invisible flame
-Hydrogen in air mixture of 4-74.2% flammable mixture
-hydrogen in air mixture of 8.2-58.9% is explosive

Question 15

How far must ignition sources be from hydrogen system ?

Answer 15

Kept at least 25 ft away from any hydrogen sources

Question 16

How far do combustion sources need to be away from hydrogen system ?

Answer 16

50 ft away

Question 17

When working on hydrogen system what must you remember ?

Answer 17

-Non sparking tools(Brass or aluminum)
-make sure excessive torque isn’t applied to valves or regulators

Question 18

What must be done when venting gas during hydrogen fill process ?

Answer 18

-Carefully monitor and control to prevent ignition as a result of this heat up and presence of static charge
-Minimize heat up of hydrogen gas expansion

Question 19

On loss of hydrogen system how does that affect Generator Hydrogen & CO2 system ?

Answer 19

-Inadequate hydrogen pressure in main generator will result in a reduced load due to loss of heat removal
-Generator would have to be shutdown if hydrogen pressure can’t be restored

Question 20

How would a loss of hydrogen system affect Chemical& Volume control ?

Answer 20

-If lost for a extended amount of time VCT could lose its cover gas
-Would affect oxygen scavenging in the RCS, which would cause corrosion

Question 21

What happens if hydrogen is lost for extended amount of time for the CVT system & Main Generator ?

Answer 21

-VCT will lose its cover gas and which prevents oxygen scavenging and crest chemistry concerns
-Main generator may have to operate at reduced loading or have to shutdown if it gets really low pressure