Q10 — RPS PZR Pressure Channel Failure
012 RPS-K4.05 (2.7)
Given:
• Unit 2 is at 100% Reactor Power and stable
• The PZR Pressure Transmitters read the following:
Which ONE of the following completes the statements below concerning the design of the Reactor Protection System (RPS)?
With 2PT-456 failed low, the coincidence for the PZR Pressure LOW Reactor Trip (based on the remaining functional PZR Pressure Channels) is now ___
• Unit 2 is at 100% Reactor Power and stable
• The PZR Pressure Transmitters read the following:
| CH I | CH II | CH III | CH IV | |
| 2PT-455 | 2PT-456 | 2PT-457 | 2PT-474 | 2PT-1648 |
| 2235 PSIG | 0 PSIG | 2235 PSIG | 2235 PSIG | 2235 PSIG |
With 2PT-456 failed low, the coincidence for the PZR Pressure LOW Reactor Trip (based on the remaining functional PZR Pressure Channels) is now ___
A. 2 out of 4
B. 1 out of 4
C. 2 out of 3
D. 1 out of 3
▶ Show Answer & Explanation
✓ D. Correct. PT-455/456/457/474 are the pressure transmitters that feed into the PZR Pressure LOW Reactor Trip coincidence (2 out of 4 below low pressure trip setpoint). With 2PT-456 failed low, the coincidence for the PZR Pressure LOW Reactor Trip (based on the remaining functional PZR Pressure Channels) is now 1 out of 3.
✗ A. Incorrect but plausible. The candidate could incorrectly conclude that PT-1648 also feeds into the PZR Pressure LOW Reactor Trip coincidence and when 2PT-456 fails, this causes the 2PT-456 bistable to be bypassed from the PZR Pressure LOW Reactor Trip. Consequently, with 2PT-456 failed low, the candidate would then incorrectly determine that the coincidence is now 2 out of 4.
✗ B. Incorrect but plausible. The candidate could incorrectly conclude that PT-1648 also feeds into the PZR Pressure LOW Reactor Trip coincidence. PT-1648 is only used for indication at the RSP. Consequently, with 2PT-456 failed low, the candidate would then incorrectly determine that the coincidence is now 1 out of 4.
✗ C. Incorrect but plausible. The candidate could incorrectly conclude that when 2PT-456 fails, this causes the 2PT-456 bistable to be bypassed from the PZR Pressure LOW Reactor Trip. Consequently, coincidence for the PZR Pressure LOW Reactor Trip would be 2 out of 3.
Ref: NOS05RXPROT-12 (Reactor Protection System) | LO: NOS05RXPROT-12 — Describe the design bases of the RPS including redundancy, independence, fail safe, testability | Source: New | Cognitive: Higher
Connections
- Related systems: RPS/SSPS, Pressurizer Level & Press Control
- Related exam: 2018 NRC Written Exam