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Abnormals > AB.COND-0001 — Loss of Condenser Vacuum

AB.COND-0001 — Loss of Condenser Vacuum

⚠️ DRAFT

AB.COND-0001 — Loss of Condenser Vacuum

Purpose

Provides guidance for responding to a loss of condenser vacuum, including actions to identify the cause, start available vacuum pumps, and stabilize condenser backpressure before plant protective actions (turbine trip) are required.

Entry Conditions

  • Condenser backpressure rising unexpectedly
  • Loss of one or more vacuum pumps
  • OHA alarms indicating condenser vacuum degradation

Key Actions

  • Initiate Attachment 1 CAS (Continuous Action Summary)
  • Dispatch operator to perform Attachment 2, Loss of Vacuum Local Checks
  • Start all available vacuum pumps
  • Manually open vacuum pump discharge air-operated valves (e.g., 25AR25) if they fail to open automatically
  • Monitor condenser backpressure for recovery
  • If backpressure continues to rise, evaluate need for load reduction or reactor trip per CAS criteria

Exam History

Scenario — 2022 #1
Event 2: 24 Vacuum Pump trips. PO enters AB.COND-0001. PO initiates Att 1 CAS, dispatches operator for Att 2 local checks. PO starts all available vacuum pumps — 22 Vacuum Pump trips after starting, 25 Vacuum Pump starts but 25AR25 fails to open and must be manually opened. Backpressure stabilizes.
Scenario — 2020 #2
Event 3: 24 Vacuum Pump trips. PO enters AB.COND-0001. Dispatches operator for Att 2 local checks — reports no abnormal conditions except breaker tripped open. PO starts all available vacuum pumps. 22 Vacuum Pump trips after start; 25AR25 fails to open on 25 Vacuum Pump start — PO manually opens 25AR25. Backpressure improves.
Exam — 2019 Q92
AB.COND-0001 CAS actions based on reactor power relative to P-9: at 45% power (below P-9), when condenser backpressure exceeds the limit of Attachment 4, the crew will trip the TURBINE (not the Reactor). After the turbine trip, crew will perform AB.COND-0001 concurrently with AB.TRB-0001 (Turbine Trip Below P-9). Trap: if power had been above P-9, the crew would trip the Reactor (and transition to EOP-TRIP-1 without performing AB.COND-0001 concurrently). Below P-9, it is a turbine trip only, and the AB procedures are performed concurrently.
Exam — 2019 Q70
CAS reactor trip criteria: if the turbine load reduction rate needs to increase to a MINIMUM of 5 % / min to stabilize condenser backpressure, the crew is REQUIRED to TRIP the Reactor. All distractors (15, 10, 7.5 %/min) are plausible because load reductions up to 15%/min are within the capability of rod control and steam dumps — but the CAS-directed trip threshold is specifically 5%/min.
Scenario — 2019 #3
Loss of Main Condenser vacuum at ~89% power due to missing tube plug in 21A waterbox during cleaning (Event 4). Rising condenser backpressure — crew starts all available vacuum pumps and manually opens AR25 valves. Vacuum stabilizes then continues to degrade. CRS enters AB.LOAD-0001 and directs load reduction to stabilize backpressure. Field report of missing tube plug — backpressure recovers after plug reinstalled.

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