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Exams > 2023 Q34 — MPC Fails Low / PZR Pressure Response

2023 Q34 — MPC Fails Low / PZR Pressure Response

⚠️ DRAFT
Q34 — MPC Fails Low / PZR Pressure Response 010 K4.03 (3.9)
Given:
• Salem Unit 2 is at 100% power
• Master Pressure Controller (MPC) is in AUTO
• PZR Pressure Channel I is selected for Control
• PZR Pressure Channel IV is selected for Alarm
Then:
• A malfunction with the MPC causes the output demand to fail LOW (0%)

Which of the following identifies the effect on RCS pressure and the expected system response, assuming no operator action?

RCS pressure will...
A. RCS pressure lowers; no backup heaters energize.
B. RCS pressure lowers; both backup heater groups energize.
C. RCS pressure rises; no PORVs open.
D. RCS pressure rises; BOTH PORVs will open.
▶ Show Answer & Explanation
✓ D. Correct. MPC fails low (0%): spray valves close (MPC controls spray), both backup heater groups energize (0% demand energizes backup heaters). RCS pressure rises with heaters on and no spray. PZR sprays will not open since MPC controls them and MPC output is at 0%. PORVs open when pressure exceeds 2335 psig — PORVs are interlocked directly from PZR pressure channels, NOT from MPC. Both PORVs will open.
✗ A. Incorrect. MPC output at 0% energizes backup heaters (not de-energizes them) and closes spray valves. With heaters on and no spray, pressure rises, not lowers.
✗ B. Incorrect. Both backup heater groups do energize (correct part), but the result is pressure rising, not lowering. With heaters on and spray valves closed, RCS pressure increases.
✗ C. Incorrect. Pressure does rise (correct part), but PORVs WILL open. PORVs are NOT controlled by MPC; they are interlocked directly from PZR pressure channels and open independently when pressure exceeds 2335 psig.
Ref: NOS05PZRPL-12, S2.OP-AB.PZR-0001 (R20) | Source: New | Cognitive: Comprehension/Analysis

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