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Exams > 2020 Q56 — Rod Drive MG Set Power Supplies

2020 Q56 — Rod Drive MG Set Power Supplies

⚠️ DRAFT
Q56 — Rod Drive MG Set Power Supplies 001000K2.05 (3.1)
Given:
• Unit 1 is operating at 100% Power.
• The 1E 460 volt bus is de-energized following a trip of its feeder breaker.
• Tagging is in progress to allow troubleshooting of 1E 460 volt bus.

The operator mistakenly opens the 1F 460 volt bus feeder breaker, de-energizing the 1F 460 volt bus.

What is the consequence, if any, of this action?
A. The Reactor will trip due to the loss of BOTH Rod Drive Motor Generators.
B. The Reactor will trip due to the loss of a SINGLE Rod Drive Motor Generator.
C. The Reactor will NOT trip because BOTH Rod Drive Motor Generators are still in service.
D. The Reactor will NOT trip because ONE Rod Drive Motor Generator is sufficient to maintain power to the Rod Control System.
▶ Show Answer & Explanation
✓ D. Correct. The 1E 460V bus supplies power to the 11 MG set, but 12 MG set is powered from the 1G 460V bus. Therefore, one MG set is still powered and is sufficient to maintain power to the Rod Control System.
✗ A. Incorrect. Plausible because the candidate may believe that the power supplies to the MG sets are 1E & 1F 460V buses.
✗ B. Incorrect. Plausible because the candidate may believe that the loss of a single MG set is enough to cause the reactor to trip.
✗ C. Incorrect. Plausible because the candidate may believe that the power supplies to the MG sets have not been affected by the actions described in the stem.
Ref: 1-EOP-TRIP-1, Reactor Trip or Safety Injection | LO: N/A | Source: Bank, Salem Vision Database | Cognitive: Fundamental

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