Q31 — RHR HX Cooldown Rate Control
005000K6.03 (2.5)
Given:
• Unit 2 is in MODE 5.
• 21 RHR HX Loop is providing Shutdown Cooling with a cooldown rate of 20 °F/hr.
• 21RH18, RHR HX Flow Control Valve, is throttled at 40 % to maintain total flow at 2500 gpm.
• 2RH20, RHR HX Bypass Valve, is throttled at 30 % open.
Subsequently the following occurs:
• Foreign material dropped in the Refueling Cavity is introduced into the RHR system causing partial blockage on the 21 RHR HX tubes.
• Cooldown rate has lowered to 5 °F/hr.
Based on the above conditions, in order to maintain a 20 °F/hr cooldown rate, the operator will be required to _______. (Assume decay heat load remains constant)
• Unit 2 is in MODE 5.
• 21 RHR HX Loop is providing Shutdown Cooling with a cooldown rate of 20 °F/hr.
• 21RH18, RHR HX Flow Control Valve, is throttled at 40 % to maintain total flow at 2500 gpm.
• 2RH20, RHR HX Bypass Valve, is throttled at 30 % open.
Subsequently the following occurs:
• Foreign material dropped in the Refueling Cavity is introduced into the RHR system causing partial blockage on the 21 RHR HX tubes.
• Cooldown rate has lowered to 5 °F/hr.
Based on the above conditions, in order to maintain a 20 °F/hr cooldown rate, the operator will be required to _______. (Assume decay heat load remains constant)
A. Lower the demand on the 21RH18 and Lower the demand on the 2RH20.
B. Lower the demand on the 21RH18 and Raise the demand on the 2RH20.
C. Raise the demand on the 21RH18 and Raise the demand on the 2RH20.
D. Raise the demand on the 21RH18 and Lower the demand on the 2RH20.
▶ Show Answer & Explanation
✓ D. Correct. Raising the controller demand for the 21RHR18 will increase flow through the RHR HX and lowering the controller demand for the 2RH20 will decrease the RHR HX bypass flow.
✗ A. Incorrect. Plausible because the candidate may confuse system configuration and valve demand operation and believe that this will increase flow through the heat exchanger.
✗ B. Incorrect. Plausible because the candidate may confuse system configuration and valve demand operation and believe that this will increase flow through the heat exchanger.
✗ C. Incorrect. Plausible because the candidate may confuse system configuration and valve demand operation and believe that this will increase flow through the heat exchanger.
Ref: S2.OP-SO.RHR-0001(Q), Initiating RHR | LO: N/A | Source: Bank Modified – 2015 Beaver Valley RO #31 | Cognitive: Comprehension
Connections
- Related systems: RHR
- Related procedures: S2.OP-SO.RHR-0001 — Initiating RHR
- Related exam: 2020 NRC Written Exam