Section 3.7.4 Atmospheric Dump Valves (ADVs)

Question 1

What is 3.7.4 Atmospheric Dump Valves (ADVs)?

Answer 1

One ADV per steam generator shall be OPERABLE.

During Modes 1, 2, 3

AND

Mode 4 when steam generator is being relied upon for heat removal.

Question 2

What are the actions of 3.7.4 Atmospheric Dump Valves (ADVs)?

Answer 2

One required ADV inoperable. Restore ADV to OPERABLE status. 7 Days.

Two required ADVs inoperable. Restore one ADV to OPERABLE status. 24 hours.

Not met. Be in Mode 3 in 6 hours and Mode 4 in 30 hours (with no reliance on SG for heat removal).

Question 3

What is the purpose and use of the atmospheric steam dump valves?

Answer 3

Purpose

Decay heat removla if the preferred heat sink via the turbine bypass valve to the condenser is not available

• Done in conjunction with the Auxiliary Feedwater System providing cooling water from the Condensate Storage Tank (CST).

Use

During normal cooldown when steam pressure drops too low for maintenance of a vacuum in the condenser to permit use of the turbine bypass valve.

Question 4

Why is one ADV per generator required?

Answer 4

To lower steam generator pressure to 885 psig in the event Auxiliary Feedwater Pump P-8C is needed to supply the steam generators for decay heat removal.

Question 5

Why do the ADVs have manual isolation valves?

Answer 5

A means of isolation in the event an ADV spuriously opens, or fails to close during use.

• ADV is NOT operable when its manual isolation valve is closed.

Question 6

What is the design basis of the ADVs?

Answer 6

• To prevent lifting of the Main Steam Safety Valves (MSSVs) following a turbine and reactor trip.
• To provide the capability to cool the plant to SDC System entry conditions when condenser vacuum is lost, making the turbine bypass valve unavailable.

Question 7

The ADVs have nitrogen backup from the bulk system. Is this required?

Answer 7

Not required to be declared OPERABLE.

Question 8

Failure to meet the LCO can result in what?

Answer 8

The inability to supply the required AFW flow rate to the steam generators assumed by the loss of normal feed flow analysis.

Question 9

What makes an ADV operable?

Answer 9

Operable when:

• it is capable of providing a controlled relief of the main steam flow
• It is capable of fully opening and closing on demand from either
  
  • control room

OR

• C-33.

Question 10

Why is seven days allowed for one inoperable ADV?

Answer 10

The 7 day Completion Time takes into account the redundant capability afforded by the remaining OPERABLE ADV, and a nonsafety grade backup in the turbine bypass
valve and MSSVs.