Q30 — RHR Cooldown Rate Control / RH18 and RH20 Valves
005 A4.02 (3.9)
Given:
• Salem Unit 1 is in MODE 4 performing a shutdown.
• 11 RHR Pump is in service
• 11 RHR Heat Exchanger is in service
• 11RH18 and 12RH18, RHR HX Flow Cont. Valves, are being throttled
• 1RH20, RHR HX Bypass Valve, is being throttled
• The BOP operator has determined that the cooldown is approaching the maximum allowable Technical Specification limit
Which of the following describes the actions that the operator will take to LOWER the cooldown rate while maintaining a constant RHR flow rate?
• Salem Unit 1 is in MODE 4 performing a shutdown.
• 11 RHR Pump is in service
• 11 RHR Heat Exchanger is in service
• 11RH18 and 12RH18, RHR HX Flow Cont. Valves, are being throttled
• 1RH20, RHR HX Bypass Valve, is being throttled
• The BOP operator has determined that the cooldown is approaching the maximum allowable Technical Specification limit
Which of the following describes the actions that the operator will take to LOWER the cooldown rate while maintaining a constant RHR flow rate?
A. Lower RH18 demand; Raise RH20 demand.
B. Raise RH18 demand; Lower RH20 demand.
C. Lower RH18 demand; Lower RH20 demand.
D. Raise RH18 demand; Raise RH20 demand.
▶ Show Answer & Explanation
✓ A. Correct. Lower demand on RH18s closes them, reducing flow through the RHR heat exchanger. Raise demand on RH20 opens the bypass valve, routing more flow around the heat exchanger. Total RHR flow stays constant, but less flow passes through the heat exchanger, reducing the cooldown rate.
✗ B. Incorrect. Raising RH18 demand opens the HX flow path more, and lowering RH20 demand closes the bypass. This increases flow through the heat exchanger and raises the cooldown rate — the opposite of what is needed.
✗ C. Incorrect. Lowering both RH18 and RH20 demand closes both the HX flow path and the bypass path. This would lower cooldown rate but also lower total RHR flow, which is not desired.
✗ D. Incorrect. Raising both demands opens both paths. This may not significantly change the cooldown rate (flow split stays similar) and would increase total RHR flow rather than maintaining it constant.
Ref: NOS05RHR000-19 | Source: Modified - Salem 2020 NRC RO31 | Cognitive: Comprehension/Analysis
Connections
- Related systems: RHR
- Related exam: 2023 NRC Written Exam