Q19 — AFW SEC Mode 2 Start
061 AFW-K2.02 (3.7)
Given:
At time 16:00
• Unit 2 is at 15% Reactor Power
• 21 SGFP is running
At time 16:01
• 2B 4KV Vital Bus de-energizes and 2B SEC starts its blackout sequencing
• A Reactor Trip occurs
The following parameters vary over time:
Which ONE of the following completes the statement below?
At 16:05, ___ AFW Pump(s) is/are running.
At time 16:00
• Unit 2 is at 15% Reactor Power
• 21 SGFP is running
At time 16:01
• 2B 4KV Vital Bus de-energizes and 2B SEC starts its blackout sequencing
• A Reactor Trip occurs
The following parameters vary over time:
| Time | 16:00 | 16:01 | 16:02 | 16:04 | 16:05 |
|---|---|---|---|---|---|
| 21 SG NR Level (%) | 33.1 | 20.7 | 21.5 | 22.7 | 23.7 |
| 22 SG NR Level (%) | 33.3 | 20.6 | 21.3 | 22.4 | 23.5 |
| 23 SG NR Level (%) | 33.1 | 19.6 | 17.6 | 15.5 | 14.4 |
| 24 SG NR Level (%) | 33.0 | 19.6 | 18.2 | 16.1 | 14.6 |
| 21 SGFP Status | Running | Running | Running | Running | Running |
Which ONE of the following completes the statement below?
At 16:05, ___ AFW Pump(s) is/are running.
A. NO Motor Driven
B. BOTH Motor Driven
C. ONLY 22
D. ONLY 21
▶ Show Answer & Explanation
✓ C. Correct. MDAFW Pumps will automatically start under the following situations: SG Level lo-lo (2/3 on 1/4 SGs <14%), Both SGFP trip, AMSAC (associated train), SEC (all modes). Since 2B SEC has actuated in Mode 2 and 22 AFW Pump is powered from 2B 4KV Vital Bus, the 22 AFW will be running at 16:05. (SEC loading should be completed by 16:01)
✗ A. Because ALL SG NR levels are above 14%, the candidate could incorrectly conclude that NO Motor Driven AFW Pumps are running at 16:05.
✗ B. Since 2 out of 4 SG NR levels are below 16% (Reactor Trip Setpoint for LO-LO SG NR Level), the candidate could incorrectly conclude that BOTH Motor Driven AFW Pumps are running at 16:05.
✗ D. The candidate could correctly determine that the SEC operating in Mode 2 will start an AFW pump. The candidate could incorrectly conclude that 21 AFW Pump is powered from 2B Vital Bus and that ONLY 21 AFW Pump is running at 16:05.
Ref: NOS05AFW000-16 (Auxiliary Feedwater System) | LO: NOS05AFW000-16 LO 5 — State the power supply to Motor-driven AFW Pumps | Source: New | Cognitive: Higher
Connections
- Related systems: AFW, SECs, 4KV
- Related exam: 2019 NRC Written Exam