Q50 — Natural Circulation Monitoring
EPE: 011 EK1.01 (4.1)
Given:
• The crew is performing 1-EOP-LOCA-2 (Post LOCA Cooldown and Depressurization) Step 29, "Monitor For Natural Circulation Flow"
• The RO observes the following:
◦ CETs are 600 °F and stable
◦ RCS Pressure is 1645 psig and slowly lowering
◦ 11 SG pressure is 725 psig and stable
◦ 11 T-COLD is 509 °F and stable
◦ 11 T-HOT is 530 °F and stable
In accordance with 1-EOP-LOCA-2, which ONE of the following completes the statements below?
Natural Circulation _(1)_ established.
If Natural Circulation is NOT established, the crew will _(2)_ 11 SG steam dumping rate.
• The crew is performing 1-EOP-LOCA-2 (Post LOCA Cooldown and Depressurization) Step 29, "Monitor For Natural Circulation Flow"
• The RO observes the following:
◦ CETs are 600 °F and stable
◦ RCS Pressure is 1645 psig and slowly lowering
◦ 11 SG pressure is 725 psig and stable
◦ 11 T-COLD is 509 °F and stable
◦ 11 T-HOT is 530 °F and stable
In accordance with 1-EOP-LOCA-2, which ONE of the following completes the statements below?
Natural Circulation _(1)_ established.
If Natural Circulation is NOT established, the crew will _(2)_ 11 SG steam dumping rate.
A. _(1)_ is / _(2)_ raise
B. _(1)_ is / _(2)_ lower
C. _(1)_ is NOT / _(2)_ raise
D. _(1)_ is NOT / _(2)_ lower
▶ Show Answer & Explanation
✓ A. Correct. For Part 1 and IAW 1-EOP-LOCA-2 Step 29, to have proper Natural Circulation flow, the following are required:
• RCS Subcooling based on CETs > 0°F
• RCS Subcooling is 9°F (TSAT for 1645 psig (1660 psia — RCS Pressure) is 609°F and CETs are 600°F)
• SG Pressure stable or lowering (11 SG pressure is 725 psig and stable)
• RCS THOT stable or lowering (Loop 1 THOT is 530°F and stable)
• CETs stable or lowering (CETs are 600°F and stable)
• 11 SG pressure at saturation pressure for RCS TCOLD temperature.
• 11 TCOLD is 509°F (PSAT is 725 psig or 740 psia) and 11 SG pressure is 725 psig
Consequently, natural circulation flow is indicated. For Part 2, 1-EOP-LOCA-2 Step 29, "Raise steam dumping rate to establish natural circulation flow."
• RCS Subcooling based on CETs > 0°F
• RCS Subcooling is 9°F (TSAT for 1645 psig (1660 psia — RCS Pressure) is 609°F and CETs are 600°F)
• SG Pressure stable or lowering (11 SG pressure is 725 psig and stable)
• RCS THOT stable or lowering (Loop 1 THOT is 530°F and stable)
• CETs stable or lowering (CETs are 600°F and stable)
• 11 SG pressure at saturation pressure for RCS TCOLD temperature.
• 11 TCOLD is 509°F (PSAT is 725 psig or 740 psia) and 11 SG pressure is 725 psig
Consequently, natural circulation flow is indicated. For Part 2, 1-EOP-LOCA-2 Step 29, "Raise steam dumping rate to establish natural circulation flow."
✗ B. Incorrect but plausible. Part 1 is correct. For Part 2, the candidate could incorrectly conclude that raising 11 SG pressure (which is caused by lowering steam dumping rate) will establish natural circulation flow.
✗ C. Incorrect but plausible. For Part 1, since there are 5 separate evaluations required to determine if natural circulation has been established, the candidate could incorrectly perform one of the evaluations and determine that natural circulation is not established. Part 2 is correct.
✗ D. Incorrect but plausible. For Part 1, since there are 5 separate evaluations required to determine if natural circulation has been established, the candidate could incorrectly perform one of the evaluations and determine that natural circulation is not established. For Part 2, the candidate could incorrectly conclude that raising 11 SG pressure (which is caused by lowering steam dumping rate) will establish natural circulation flow.
Ref: 1-EOP-LOCA-2 (Post LOCA Cooldown and Depressurization) | LO: NOS05LOCA02-03 LO 5 | Source: New | Cognitive: Higher
Connections
- Related systems: RCS, Steam Generator & Blowdown
- Related EOPs: EOP-LOCA-2 — Post LOCA Cooldown and Depressurization
- Related exam: 2018 NRC Written Exam