Loss of Condenser Vacuum

Question 1

State how one of the listed problems would affect Cond. Vacuum.(not all inclusive of what could cause problems)

Circ Water

Air in-leakage

Environmental

Answer 1

• Circwater:
  
  • CW pump trip or clogged intake screens - reduced CW mass flowrate
  • Cooling tower loss - loss of heat removal capacity.
• Air inleakage:
  
  • Loss of GS steam, faulty GS regulator.
  • Air inleakage from Vac breaker seal, dogbone seals, at condenser shell, expansion joints, or other areas where vacuum and atompshere are present.
• Environmental:
  
  • Hi relative humidity, outside air temperatures or abnormal wind conditions.

Question 2

What components are affected by rising condenser vacuum?

Answer 2

> 5.5” SBCS cond interlock

> 7.5” Tur trip

> 13.5” MFP trip

Question 3

State the Rx and turbine trip criteria associated with Cond Vacuum.

Answer 3

Generator On-line:

• > 7” HgA and ↑ (Turbine trip imminent and SBCS is not available)
• < 410 MWe and > 5” HgA (ARP for Low vacuum directs a Turbine trip, AOP directs Reactor trip)
• < 410 MWe and > 4” HgA for > 1 hour
• Generator on-line < 70 MWe and load reduction is needed

Generator NOT on-line:

• PRX > 12% and SBCS Cond interlock actuated (5.5” HgA) (exceeds capacity of 1007/1008)
• PRX 3-12%, SBCS Cond interlock actuated, > 7” HgA and ↑, and MFPs are tripped

Turbine Trip Criteria

• Generator NOT on-line, SBCS Cond interlock actuated, PRX ≤ 12%, and > 7” HgA and ↑

Question 4

What are the consequences of NOT taking CEDMCS out of AUTO when transitioning to SBCS 1007/1008?

Answer 4

This will cause RRS to drive CEAs in on the percieved Tave - Tref mismatch due to TLI being driven low by transitioning to SBCS. Actual Tave would lower until operator action was taken or the Rx tripped on Ppzr low.

Question 5

Where should SG pressure be maintained when transitioning to SBCS valves 1007 or 1008?

Answer 5

SG pressure should be maintained less than the SBCS automatic setpoint and RCS temperature +/-3F.

Question 6

How does a loss of Cond Vacuum impact hotwell level control and what actions are necessary to maintain the level?

Answer 6

Lowering vacuum will prevent hotwell makeup to condenser due to inadequate d/p from CST and condenser. If < 41” hotwell level then direct an operator to use hotwell makeup bypass to raise hotwell level.

Question 7

What are the concerns of a dropping hotwell level during plant operation?

Answer 7

If hotwell level drops < 30 “ in a particular shell with a running condensate pump, that pump will trip. If a HDP were to trip an expected hotwell level drop of 9” would occur until the system stabilized out.

Question 8

How is SBCS system reset following a condenser interlock?

Answer 8

If Cond vacuum went above >5.5”, after it returned to below 5.5” you must reset the cond interlock by using the emergency off switch on B06. Ensure SBCS master is in L Manual.