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Exams > 2022 Q57 — IR NIS Channel Failure and P-10 Permissive

2022 Q57 — IR NIS Channel Failure and P-10 Permissive

⚠️ DRAFT
Q57 — IR NIS Channel Failure and P-10 Permissive 015 K4.07 (3.7)
Given:

• Unit 2 is performing a planned shutdown for a refueling outage.
• Current reactor power is 30%.
• 2N35, Intermediate Range NIS channel fails HIGH.

Which ONE of the following describes the plant impact from this failure?
A. Reactor trips immediately on 1/2 Intermediate Range channels exceeding the high flux trip.
B. Reactor trips ONLY when 2/2 Intermediate Range channels exceed the high flux trip.
C. Reactor trips when 3/4 Power Range channels are less than the P-10 permissive.
D. Reactor trips when 2/4 Power Range channels are less than the P-10 permissive.
▶ Show Answer & Explanation
✓ C. Correct. When at least 3/4 PR NIS channels are less than P-10 setpoint (approx. 9%), P-10 will automatically unblock and reinstate the 1/2 IR high flux trip (25%) and 2/4 PR high flux low setpoint trip (25%). In this case, with the 2N35 failed high, the Rx will automatically trip when below P-10 permissive.
✗ A. P-10 (2/4 PR channels > 10%) is blocking the 1/2 IR high flux trip. Plausible because the operator may incorrectly assess the plant conditions and believe that a Rx trip will occur when one IR channel fails high.
✗ B. P-10 (2/4 PR channels > 10%) is blocking the 1/2 IR high flux trip. Plausible because the operator may incorrectly believe that both (2/2) IR channels exceeding the high flux setpoint are required to cause a Rx trip.
✗ D. When at least 3/4 PR NIS channels are less than P-10 setpoint (approx. 9%), P-10 will automatically unblock and reinstate the 1/2 IR high flux trip (25%) and 2/4 PR high flux low setpoint trip (25%). Plausible because the operator may incorrectly determine that P-10 permissive will clear when 2/4 PR channels are less than the P-10 permissive.
Ref: NOS05EXCORE-14 | LO: NOS05EXCORE-14, Obj 7 — Outline the control interlocks associated with Excore NIS: P-10, Enable At-Power trips | Source: Bank — Salem | Cognitive: Comprehension/Analysis

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