Primary Vent System

Question 1

What is purpose of the Primary Coolant Gas Vent System?

Answer 1

Designed to vent steam or noncondensible gases from the Reactor Vessel head and Pressurizer under post accident conditions.

May also be used to aid in the pre- or post-refueling venting of the PCS. Vent flow is directed to the Primary System Drain Tank or Waste Gas System via the Quench Tank to prevent inadvertent release of radioactive fluid to Containment.

Question 2

PRV-1067, PRV-1068 Reactor Head Vent Valves power supplies and design.

Answer 2

PRV-1067, Reactor Head Vent Valve

• D-11-1

PRV-1068, Reactor Head Vent Valve

• D-21-1

Solenoid pilot operated valves.

• One inch diameter
• Rated for 2500 psia
• 650°F.

The valves are in parallel and are powered from separate DC Buses.

Question 3

PRV-1069 and PRV-1070, Pressurizer Vent Valves power supplies and design.

Answer 3

PRV-1069, Pressurizer Vent Valve

• D-11-1

PRV-1070, Pressurizer Vent Valve

• D-21-1

Solenoid pilot operated valves.

• One inch diameter
• Rated for 2500 psia
• 650°F.
• The valves are in parallel and are powered from separate DC Buses.

Question 4

What are RO-0101, Reactor Head Restricting Orifice and RO-0102, Pressurizer Restricting Orifice?

Answer 4

Reactor Head and Pressurizer Restricting Orifice

• 1” size, rated at 2500 psig.
• It is placed as close to the Reactor Vessel or Pressurizer as possible to limit the possibility of an uncontrolled Loss of Coolant Accident.
• Sized to limit mass loss from a line break to less than the makeup capability of a single charging pump.

Question 5

Describe PRV-1071, PCS Vent to Containment

Answer 5

PRV-1071, PCS Vent to Containment

• Powered from D11-1

Solenoid pilot operated valve

• One inch nominal diameter
• Rating of 2500 psia and 650°F.
• Discharges to the open area of Containment above the Pressurizer Shed where adequate mixing with the Containment atmosphere is assured. .

Question 6

Describe PRV-1072, PCS Vent to the Quench Tank

Answer 6

PRV-1072, PCS Vent to the Quench Tank

• Powered from D21-1

Solenoid pilot operated valve

• One inch nominal diameter
• Rating of 2500 psia and 650°F.
• Discharges to the common header which routes the discharges from the PZR Code Safety Valves and the PORVs to the Quench Tank.

Question 7

Draw the Primary Vent System

Answer 7

Per Attachment 2 of Lesson Plan

Question 8

EOP Supplement 26 Section 3.0, “Non-Condensible Void Removal, Reactor Vessel Head.”

Answer 8

• Venting through PRV‑1072 to the Quench Tank (preferred)
• Or through PRV-1071 to Containment

Reactor Void Removal

• PRV-1067 or PRV-1068 is opened to start the vent

Pressurizer Void Removal

• PRV-1069 or PRV-1070 is opened to start the vent

Question 9

After depressurization, how is first drain vented?

Answer 9

The first drain after depressurization both the Pressurizer and the Reactor Head are vented via MV-PC1044A and MV-PC1044B.

Question 10

What are the control room valve controls and indication.

Answer 10

There are six valve control circuits, one for each valve.

• PRV-1067/1068 Reactor Vent Valves
• PRV-1069/1070 Pressurizer Vent Valves
• PRV-1071, PCS Vent to Containment
• PRV-1072, PCS Vent to Quench Tank

Each valve is controlled by a keyswitch with an “OPEN”, “CLOSE”, and “RESET” position each with an open and closed indication.

Loss of power, KS must be taken to Close. This feature ensures the PRV’s do not re‑open on a loss of power and subsequent re‑energization.

Question 11

What alarms?

Answer 11

No Alarms

Question 12

What are control room indications of PVS?

Answer 12

Valve positions

The Gas Vent Header pressure of the common discharge line is indicated in the Control Room on PIA-1066.

Question 13

How does the Primary Vent System interact with H2 Monitoring?

Answer 13

System is designed to vent gases into Containment, the EOPs direct a hydrogen monitor be in operation to detect for excessive hydrogen concentration.

Question 14

How does the Primary Vent System interact with Containment Cooling?

Answer 14

Containment Air Cooler fans (V-1A/B, 2A/B, 3A/B, 4A/B) ensure mixing of containment atmosphere for representative sampling.

Question 15

How does the Primary Vent System interact Station Power?

Answer 15

Odd numbered (PRV-1067, PRV-1069 and PRV-1071)

• Powered from D11-1.

Even numbered (PRV-1068, PRV-1070 and PRV-1072)

• Powered from D21-1.

PIA-1066 is powered from L-08 Breaker 1 via Bus 1C/LCC-13/MCC-3

Question 16

What are the potential sources of non-condensible gases in the PCS?

Answer 16

• Clad oxidation from long-term core uncovery
• Gaseous fission products released due to fuel failure
• Dissolved gases coming out of solution during PCS depressurization
• Nitrogen from the Safety Injection Tanks
• Radiolytic decomposition of water by fission product decay

Question 17

What are possible indications of voiding?

Answer 17

• Indicated Charging and Letdown flows do not correspond to pressurizer level trend.
• Pressurizer level is rising significantly faster than trend expected for Auxiliary Spray Flow.
• Core ∆T (Average of Qualified CETs – TC) or Loop ∆T (TH – TC) rising for same secondary steaming and Auxiliary Feed rates.
• Any operable PCS temperature indication is less than 25°F subcooled.
• Operable RVLMS indicates voiding in the Reactor Vessel.

Question 18

What actions are taken for voiding?

Answer 18

• If PCS pressure reduction or PCS heat removal is inhibited, then void elimination action should take place.
• EOP 4.0 is the primary guidance document and will direct use of EOP Supplement 26.
• The actions to mitigate voids will consist mostly of removing condensible voids, since those are the most likely to be affecting a safety function.
  
  • Primary Coolant Gas Vent System is only used for non-condensible void removal.

Question 19

What are the requirements of ORM 3.1.10, Primary Coolant Gas Vent System

Answer 19

Applicable in Modes 1, 2 and 3 with PCS temperature > 525°F

The following Primary Coolant System vent paths consisting of at least two valves in series shall be OPERABLE and closed.

• Reactor vessel vent path to Containment and Reactor Vessel vent to the Quench Tank
• Pressurizer vent path to Containment and Pressurizer vent to the Quench Tank

If one of the valves in parallel becomes inoperable, there is no action because the affected vent path still exists via the other valve.