2022 Q33 — ECCS Flow at 300 psig with Loss of 4KV Bus

✓ B. Correct. With 2C 4KV Vital Bus de-energized only 21 Charging Pump, 21 SI Pump, and both RHR Pumps are running. With RCS pressure at 300 psig, the Charging pump is running at runout flow condition which is 560 gpm per pump. The SI pumps are operating at runout flow conditions which is 675 gpm per pump. The RHR pumps are running at shutoff head (>170 psid) so no flow is expected. Therefore, total ECCS flow at 300 psig = 560 gpm + 675 gpm = 1235 gpm.

✗ A. Incorrect. Plausible if the operator believes that the charging pump is the only ECCS pump providing flow and all other pumps are above their shutoff head. This is the total flow for 1 charging pump.

✗ C. Incorrect. Plausible if the operator believes that both SI pumps are still running and doesn't take into account that the 2C 4KV bus supplies one of the SI pumps. This is the total flow with 1 charging pump and 2 SI pumps running.

✗ D. Incorrect. Plausible if the operator believes that the RHR pumps are below their shutoff head. RHR is placed in service during shutdown when RCS pressure is below 340 psig. The RHR pumps are at shutoff head so no flow is expected with RCS pressure at 300 psig. The RHR pumps can only deliver design accident flow of 4500 gpm when RCS pressure is less than 170 psid or 170 psig during injection. This is the total flow with 1 Charging, 1 SI, and 2 RHR pumps running [560 gpm + 675 gpm + 4500 x 2 = 10235 gpm].

Ref: NOS05ECCS00-10 & NOS05RHR000-19 | LO: NOS05ECCS00-10, Objective 16 — Given an Emergency Core Cooling System failure, predict the effect of the Emergency Core Cooling System failure on the following: Reactor Coolant System | Source: New | Cognitive: Comprehension/Analysis