Q8 — ATWS Turbine Trip
000029EK3.12 (4.4)
Given:
• Unit 2 was at 100% Power when a trip of both Steam Generator Feed Pumps occurred.
The following sequence of events occurs:
• ALL SG NR LO-LO level setpoints are reached, but the reactor failed to trip.
• ALL attempts to trip the reactor from the control room were unsuccessful and the reactor trip is NOT confirmed.
• The crew enters 2-EOP-TRIP-1, Reactor Trip or Safety Injection.
Complete the following statements:
In accordance with 2-EOP-TRIP-1, which one of the following is the NEXT required action and why?
• Unit 2 was at 100% Power when a trip of both Steam Generator Feed Pumps occurred.
The following sequence of events occurs:
• ALL SG NR LO-LO level setpoints are reached, but the reactor failed to trip.
• ALL attempts to trip the reactor from the control room were unsuccessful and the reactor trip is NOT confirmed.
• The crew enters 2-EOP-TRIP-1, Reactor Trip or Safety Injection.
Complete the following statements:
In accordance with 2-EOP-TRIP-1, which one of the following is the NEXT required action and why?
A. Trip the Turbine to maintain steam generator inventory.
B. Start 21 and 22 AFW Pumps to maintain steam generator inventory.
C. Initiate rod insertion to insert negative reactivity.
D. Initiate rapid boration to insert negative reactivity.
▶ Show Answer & Explanation
✓ A. Correct. Although the step is included in 2-EOP-TRIP-1 as an immediate action, the bases documents for 2-EOP-FRSM-1 states that; "The turbine is tripped to prevent an uncontrolled cooldown of the RCS due to steam flow that the turbine would require. For an ATWS event where a loss of normal feedwater has occurred, analyses have shown that a turbine trip is necessary (within 30 seconds) to maintain SG inventory." The first action in TRIP-1 if the reactor trip is not confirmed is to trip the turbine.
✗ B. Plausible because the first step of 2-EOP-FRSM-1 is to initiate auxiliary feedwater and the candidate may believe it is first in TRIP-1 as well. The second part of the answer regarding the bases is correct. Incorrect the turbine is tripped in TRIP-1 prior to transition to FRSM-1 for an ATWS condition.
✗ C. Plausible because the initiation of rod insertion is a step in TRIP-1 prior to transitioning to FRSM-1. Incorrect as the step is after tripping the turbine. The second part of the answer regarding the bases is correct.
✗ D. Plausible because if BIT flow has not been established FRSM-1 initiates rapid boration. The candidate may also remember that critical task completion for an ATWS includes rapid boration as a success path when being graded on an operating exam during an ATWS event. Incorrect as rapid boration is not initiated in TRIP-1 prior to transition to FRSM-1.
Ref: 2-EOP-TRIP-1, 2-EOP-FRSM-1 and Bases | LO: N/A | Source: New | Cognitive: Fundamental
Connections
- Related systems: Main Turbine, AFW, Steam Generator & Blowdown
- Related EOPs: EOP-TRIP-1 — Reactor Trip or Safety Injection, EOP-FRSM-1 — Response to Nuclear Power Generation
- Related exam: 2020 NRC Written Exam