Q20 — AFW Pressure Override Runout Protection
061 AFW-K6.02 (2.6)
Given:
• Unit 2 is at 4% Reactor Power
• 21 and 22 AFW Pumps are feeding ALL SGs using 21-24AF21 with the following bezel indications:
PRESSURE OVERRIDE NORMAL LIGHT is illuminated
At time 12:00
• 21 AFW Pump trips
Which ONE of the following describes the INITIAL response of the AFW System?
NOTE:
• 21-24AF21 = STEAM GENERATOR INLET VALVEs
• 21-24AF11 = STEAM GENERATOR INLET VALVEs
• Unit 2 is at 4% Reactor Power
• 21 and 22 AFW Pumps are feeding ALL SGs using 21-24AF21 with the following bezel indications:
PRESSURE OVERRIDE NORMAL LIGHT is illuminated
At time 12:00
• 21 AFW Pump trips
Which ONE of the following describes the INITIAL response of the AFW System?
NOTE:
• 21-24AF21 = STEAM GENERATOR INLET VALVEs
• 21-24AF11 = STEAM GENERATOR INLET VALVEs
A. 23-24AF21 will remain in its current position and AFW flow to 23 and 24 SGs will lower to 0 LBM/HR
B. 23-24AF21 will AUTOMATICALLY close and AFW flow to 23 and 24 SGs will lower to 0 LBM/HR
C. 23 AFW will IMMEDIATELY start and will now provide feed flow to 23 and 24 SGs through 23-24AF21
D. 23-24AF21 will AUTOMATICALLY close, 23 AFW will IMMEDIATELY start and will now provide feed flow to 23 and 24 SGs through 23-24AF11
▶ Show Answer & Explanation
✓ B. Correct. Since the "Pressure Override Normal Light" for 21 AFW Pump is illuminated, 21 AFW Pump Runout protection is enabled. With runout protection enabled, 23AF21 and 24AF21 will go closed (and be prevented from being opened if the valves are already closed) when 21 AFW Pump discharge pressure is below 1085 psig. Consequently, when 21 AFW Pump Trips at 1200, 21 AFW discharge pressure will go to 0 psig. The result is that 23AF21 and 24AF21 will AUTOMATICALLY close and AFW flow to 23 and 24 SGs will go to 0 LBM/HR.
✗ A. If the "Pressure Override Defeat" light had been illuminated for 21 AFW Pump, then when 21 AFW Pump tripped at 1200, 23-24AF21 would not move and AFW flow to 23 and 24 SGs would go to 0 LBM/HR.
✗ C. 23 AFW pump does have an AUTOMATIC start feature. However, trip of a MDAFW pump will not cause the 23AFW to immediately start.
✗ D. This distractor is partially correct. 23-24AF21 will automatically close when 21 AFW pump trips. Additionally, 23 AFW pump does have an AUTOMATIC start feature. However, trip of a MDAFW pump will not cause the 23AFW to immediately start.
Ref: NOS05AFW000-16 (Auxiliary Feedwater System) | LO: NOS05AFW000-16 LO 6 — Outline the interlocks associated with AFW System components including pump automatic start, MDAFW recirculation flow control valves, and MDAFW discharge flow control valves | Source: New | Cognitive: Higher
Connections
- Related systems: AFW
- Related exam: 2019 NRC Written Exam