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Exams > 2019 Q69 — SG Tube Leak Subcooling Calculation

2019 Q69 — SG Tube Leak Subcooling Calculation

⚠️ DRAFT
Q69 — SG Tube Leak Subcooling Calculation APE: 037 Steam Generator Tube Leak-AK1.01 (2.9)
Given:
• The crew is performing S2.OP-AB.SG-0001 (STEAM GENERATOR TUBE LEAK) Step 3.37.B, "DEPRESSURIZE the RCS concurrently with cooldown AND MAINTAIN 20 to 40°F subcooling"
• The subcooling monitor is NOT functional

At time 15:00
• TAVG is 530 °F
• The Hottest CET is 540 °F
• RCS Pressure is 1200 psig

Based on information contained in Steam Tables, which ONE of the following completes the statement below?

At 15:00, the RCS is subcooled by approximately ___ °F.
A. 25
B. 29
C. 35
D. 39
▶ Show Answer & Explanation
✓ B. Correct. The candidate must first determine TSAT for 1200 psig. Since the steam tables are in PSIA, 1200 psig must be converted to PSIA: (1200 + 15) = 1215 PSIA. Using steam tables (and interpolating) TSAT of 1200 PSIG is approximately 569 °F. Subcooling is based on the Hottest CET which is 540 °F. Subcooling = TSAT - Hottest CET = 569 - 540 = 29 °F.
✗ A. Incorrect but plausible. 25 is plausible if the candidate incorrectly determines TSAT for 1200 psig to be 565 °F and correctly uses the CET reading to calculate subcooling. This would be done by incorrectly entering the steam tables at 1185 PSIA (1200 - 15 = 1185). Subcooling would then be calculated at 565 - 540 = 25 °F.
✗ C. Incorrect but plausible. 35 is plausible if the candidate incorrectly determines TSAT for 1200 psig to be 565 °F and incorrectly uses TAVG to calculate subcooling. This would be done by incorrectly entering the steam tables at 1185 PSIA (1200 - 15 = 1185). Subcooling would then be calculated at 565 - 530 = 35 °F.
✗ D. Incorrect but plausible. 39 is plausible if the candidate correctly determines TSAT for 1200 psig = 569 °F but incorrectly uses TAVG to calculate subcooling (569 - 530) = 39 °F.
Ref: Steam Tables | LO: NOS05ABSGTL-05 | Source: New | Cognitive: Higher

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