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Exams > 2019 Q3 — CVCS Malfunction Rod Response[EDITED]

2019 Q3 — CVCS Malfunction Rod Response[EDITED]

⚠️ DRAFT
Q3 — CVCS Malfunction Rod Response [EDITED] 004 CVCS-K3.01 (2.5)
Given:
- Unit 1 is 90% Reactor Power and stable
- The Rod Bank Selector Switch is in AUTOMATIC

At Time 07:00
- An AUTOMATIC RCS Makeup starts

At Time 07:01
- 125 VDC power to 1CV179 (PRIMARY WATER FLOW) has been lost
- The Primary Water Flow Deviation Alarm actuates

At Time 07:02
- 1CV185 (MAKEUP FLOWPATH) fails to AUTOMATICALLY close

Which ONE of the following completes the statements below?

The Primary Water Flow Deviation Alarm actuates when primary water flow is greater than a MINIMUM of ±_(1)_ gpm above the setpoint.

Control Rods are expected to step _(2)_ as the makeup continues with 1CV179 in its failed position.

NOTE: Auto Rods Out has been disabled. When answering, assume "out" means manually withdrawing rods.
A. (1) 5.0 (2) out (manually)
B. (1) 5.0 (2) in
C. (1) 0.8 (2) out (manually)
D. (1) 0.8 (2) in
▶ Show Answer & Explanation
✓ A. Correct. For Part 1 and IAW S2.OP-AR-ZZ-0012, the Primary Water Flow Deviation Alarm actuates when primary water flow is greater than a MINIMUM of ±5.0 gpm above the setpoint. For Part 2, 1CV179 fails closed. Consequently, actual boron flow out of the boric acid blender will higher than the predetermined setpoint for the auto makeup (based on current RCS Boron concentration). This will cause actual RCS boron concentration to rise since the boron concentration of auto makeup flow is higher than the setpoint for the existing RCS Boron concentration. An increase in actual RCS Boron concentration will insert negative reactivity which will cause Tavg to lower. As Tavg lowers, control rods will step out (manually) to restore Tavg to program temperature.
✗ B. Incorrect but plausible. Part 1 is correct. For Part 2, the candidate could incorrectly conclude that 1CV179 fails open. With 1CV179 fully open during an automatic RCS makeup, actual RCS Boron Concentration will lower. Lowering actual RCS Concentration will add positive reactivity which will cause the Tavg to rise. As Tavg rises, control rods will step in to restore Tavg to program temperature.
✗ C. Incorrect but plausible. For Part 1, the Boric Acid Flow Deviation actuates when boric acid flow is greater than a MINIMUM of ±0.8 gpm above the setpoint. Consequently, the candidate could incorrectly conclude that the Primary Water Flow Deviation Alarm actuates when primary water flow is greater than a MINIMUM of ±0.8 gpm above the setpoint. Part 2 is correct.
✗ D. Incorrect but plausible. For Part 1, the Boric Acid Flow Deviation actuates when boric acid flow is greater than a MINIMUM of ±0.8 gpm above the setpoint. Consequently, the candidate could incorrectly conclude that the Primary Water Flow Deviation Alarm actuates when primary water flow is greater than a MINIMUM of ±0.8 gpm above the setpoint. For Part 2, the candidate could incorrectly conclude that 1CV179 fails open. With 1CV179 fully open during an automatic RCS makeup, actual RCS Boron Concentration will lower. Lowering actual RCS Concentration will add positive reactivity which will cause the Tavg to rise. As Tavg rises, control rods will step in to restore Tavg to program temperature.
Ref: Drawing 224443, S2.OP-AR-ZZ-0012 | LO: NOS05CVCS00-17 | Source: Modified Bank (ILOT 1601 NRC RO Q31) | Cognitive: Higher

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