Q32 — RHR Pump Trip / Solid Plant Pressure Response
005 K5.05 (2.7)
Given:
• Salem Unit 2 is in MODE 5.
• The RCS is in solid plant operation at 300 psig.
• One train of RHR is in service.
• One Charging Pump is running.
• RHR letdown is in service through the 2CV8, Letdown Isolation for RHR, with all letdown orifices open.
• Letdown Booster Pump is NOT in service.
• 2CV18, Letdown Pressure Control Valve, is in AUTOMATIC.
Subsequently, the running RHR Pump trips.
Which ONE of the following completes the following statement?
Initially, RCS pressure will _(1)_, and Letdown pressure will _(2)_.
• Salem Unit 2 is in MODE 5.
• The RCS is in solid plant operation at 300 psig.
• One train of RHR is in service.
• One Charging Pump is running.
• RHR letdown is in service through the 2CV8, Letdown Isolation for RHR, with all letdown orifices open.
• Letdown Booster Pump is NOT in service.
• 2CV18, Letdown Pressure Control Valve, is in AUTOMATIC.
Subsequently, the running RHR Pump trips.
Which ONE of the following completes the following statement?
Initially, RCS pressure will _(1)_, and Letdown pressure will _(2)_.
A. _(1)_ lower; _(2)_ rise
B. _(1)_ lower; _(2)_ lower
C. _(1)_ rise; _(2)_ rise
D. _(1)_ rise; _(2)_ lower
▶ Show Answer & Explanation
✓ D. Correct. Flow into (charging) and out of (RHR letdown) the RCS was initially balanced. When RHR pump tripped two things resulted: 1) the RCS pressure rose due to the flow imbalance, and 2) letdown line pressure lowered due to the loss of discharge pressure when the RHR pump tripped. 2CV18 will respond to the lowering letdown line pressure by closing to attempt to maintain pressure at setpoint.
✗ A. Incorrect. First part is incorrect. RCS pressure rises due to charging adding inventory, while no RHR pump is running to remove inventory. Second part is incorrect. Plausible because the operator may believe that when RCS pressure lowers the 2CV18 will close more resulting in more line resistance in the letdown line and an increase in pressure due to non-compressibility of water.
✗ B. Incorrect. First part is incorrect. Second part is correct. Plausible because if RCS pressure lowers, 2CV18 would normally be expected to throttle closed.
✗ C. Incorrect. First part is correct. Second part is incorrect. The 2CV18 will throttle closed. When the RHR pump trips, RHR discharge pressure, and the pressure at the letdown line will lower. 2CV18 will throttle closed to attempt to maintain pressure. Plausible because the operator may believe that when RCS pressure rises, the 2CV18 will close more to reduce pressure resulting in more line resistance in the letdown line and an increase in pressure due to non-compressibility of water.
Ref: S2.OP-IO.ZZ-0006 (R52) | LO: NOS05CVCS00-18, Objective 4 — Describe the function and how their normal and abnormal operations affects the Chemical and Volume Control System: (x) Low Pressure Letdown Control Valve, CV18 | Source: Bank — Diablo Canyon 2016 NRC RO04 | Cognitive: Comprehension/Analysis
Connections
- Related systems: RHR, CVCS
- Related procedures: S2.OP-IO.ZZ-0006 — Hot Standby to Cold Shutdown
- Related exam: 2022 NRC Written Exam