Q3 — SBLOCA Subcooling / Steam Tables
000009EK1.02 (3.5)
Given:
• Unit 2 has experienced a Small Break LOCA with a Loss of Off-Site Power.
• A fault developed on the 2A 4KV Bus and the Bus is de-energized.
• All available ECCS Pumps are currently running.
• Containment Pressure is currently 4.3 psig.
• RCS Pressure is currently 1035 psig.
• The crew has transitioned to 2-EOP-LOCA-2, Post LOCA Cooldown and Depressurization.
• The crew is implementing "Charging Pump Reduction" major action of EOP-LOCA-2.
• Based on operability concerns with the Subcooling Margin Monitor, the CRS has directed the RO to determine subcooling requirements using Steam Tables.
Which ONE of the following choices is the MAXIMUM RCS (Core Exit) temperature that will allow stopping one Charging Pump in accordance with step 21 of 2-EOP-LOCA-2?
[REFERENCES PROVIDED]
• Unit 2 has experienced a Small Break LOCA with a Loss of Off-Site Power.
• A fault developed on the 2A 4KV Bus and the Bus is de-energized.
• All available ECCS Pumps are currently running.
• Containment Pressure is currently 4.3 psig.
• RCS Pressure is currently 1035 psig.
• The crew has transitioned to 2-EOP-LOCA-2, Post LOCA Cooldown and Depressurization.
• The crew is implementing "Charging Pump Reduction" major action of EOP-LOCA-2.
• Based on operability concerns with the Subcooling Margin Monitor, the CRS has directed the RO to determine subcooling requirements using Steam Tables.
Which ONE of the following choices is the MAXIMUM RCS (Core Exit) temperature that will allow stopping one Charging Pump in accordance with step 21 of 2-EOP-LOCA-2?
[REFERENCES PROVIDED]
A. 500°F
B. 415°F
C. 409°F
D. 407°F
▶ Show Answer & Explanation
✓ C. Correct. Only one SI Pump is running, all RCPs are stopped, and Containment Adverse conditions exist per the question stem. The required subcooling is 141°F from Table C. Using steam tables, the T-Sat for 1035 psig (1049.7 psia) is 550.56°F. Therefore the max core exit temperature that will allow stopping one Charging Pump is 409°F.
✗ A. Incorrect. Plausible because candidate may believe two SI Pumps are running and choose a required subcooling of 135°F from Table C. Incorrect because only one SI Pump is running due to the fault on 2A 4Kv Bus.
✗ B. Incorrect. Plausible because candidate may use the normal containment value and choose a required subcooling of 50°F from Table C. Incorrect because containment pressure is 4.3 psig and therefore adverse numbers apply.
✗ D. Incorrect. Plausible because candidate may incorrectly use 1035 psig instead of 1049.7 psia. Using 1035 psia, the candidate incorrectly calculates T-Sat as 548.83°F.
Ref: 2-EOP-LOCA-2, Sheet 2 | Proposed Refs: 2-EOP-LOCA-2, Post LOCA Cooldown and Depressurization, Sheet 2 & Steam Tables | LO: N/A | Source: New | Cognitive: Comprehension
Connections
- Related systems: ECCS
- Related EOPs: EOP-LOCA-2 — Post LOCA Cooldown and Depressurization
- Related exam: 2020 NRC Written Exam