Q14 — SEC Mode 2 SI Pump Status
APE 56 AA2.03 (3.8)
Given:
• Unit 2 is at 100% Power.
• The crew is performing S2.OP-ST.SJ-0001, Inservice Testing – 21 Safety Injection Pump.
• 21 SI Pump is running.
Subsequently, the following occurs;
• Loss of Offsite Power.
• OHA J-2, 2B 4KV VTL BUS DIFF PROT, is LIT
After 2 minutes has elapsed, which ONE of the following describes the operational status of the Safety Injection Pumps?
• Unit 2 is at 100% Power.
• The crew is performing S2.OP-ST.SJ-0001, Inservice Testing – 21 Safety Injection Pump.
• 21 SI Pump is running.
Subsequently, the following occurs;
• Loss of Offsite Power.
• OHA J-2, 2B 4KV VTL BUS DIFF PROT, is LIT
After 2 minutes has elapsed, which ONE of the following describes the operational status of the Safety Injection Pumps?
A. ONLY 21 SI Pump is running.
B. ONLY 22 SI Pump is running.
C. BOTH SI Pumps are running.
D. NEITHER SI Pumps are running.
▶ Show Answer & Explanation
✓ D. Correct. On a loss of offsite power the SECs will strip the loads on the 2A and 2C 4KV Vital buses, start the EDGs and close the output breakers, and then load the safeguards equipment using the load sequencer. The 21 and 22 SI pumps are powered from 2A and 2C 4KV Vital buses. Since no SI signal is present, the SECs are in Mode 2 (Blackout only). In Mode 2 the SEC load sequencers will only start the Charging Pumps. No SI or RHR pumps will be started since no SI accident signal is present. The OHA J-2 alarm identifies that the 2B 4KV Vital Bus will be de-energized and lockout, which has no impact to the SI Pumps power source. Therefore, on a Blackout only, the SI pumps will NOT start.
✗ A. Plausible distractor if the candidate believes that the 21 SI pump that was already running will remain running following SEC actuation, similar to a SEC Mode 1 (Accident only) actuation. The candidate may also believe that the OHA J-2 will prevent the start of the 22 SI Pump.
✗ B. Plausible distractor if the candidate believes that the 22 SI pump will be the only pump running based on the Bus Differential protection lockout on 2B 4KV Vital Bus affecting the 21 SI Pump. SI pumps are not powered from 2B 4KV Vital bus.
✗ C. Plausible distractor if the candidate believes that the SECs will start both SI pumps during a SEC Mode 2 (Blackout). In SEC Mode 2, only the Charging Pumps will start. The SI pumps will only start when an accident SI signal is present during an SEC Mode 1 (Accident only) or SEC Mode III or IV (Accident plus Blackout) conditions.
Ref: NOS05SEC000 | LO: NOS05SEC000-09, Objective 4 — Describe in detail each Mode of Safeguards Equipment Control System operation, including setpoints for automatic actuation | Source: Bank — Salem 2016 NRC RO19 | Cognitive: Comprehension/Analysis
Connections
- Related systems: ECCS, EDGs
- Related exam: 2022 NRC Written Exam