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Exams > 2023 Q73 — Steam Tables Subcooling and SG Pressure

2023 Q73 — Steam Tables Subcooling and SG Pressure

⚠️ DRAFT
Q73 — Steam Tables Subcooling and SG Pressure T4 193003 K1.24 (3.1)
Given:
- Salem Unit 2 is shutdown.
- RCS pressure is 1805 psig and stable.
- Core decay heat is being removed via the Steam Generators (SGs) using the MS10s, Atmospheric Dump Valves

What is the HIGHEST pressure in the SGs to obtain a MINIMUM 100 degrees F subcooling margin in the reactor coolant leaving the SGs (assume the reactor coolant leaves the SGs at the SG saturation temperature)?
A. 790 psig
B. 805 psig
C. 820 psig
D. 835 psig
▶ Show Answer & Explanation
✓ B. Correct. At 1805 psig or 1820 psia the RCS saturation temperature is 623 degrees F. Therefore, to obtain a 100 degrees F subcooling margin in the RCS loop cold legs, temperature must be 100 degrees F lower than 623 degrees F (which is equal to 523 degrees F). Because a negligible temperature difference exist across the steam generator tubes, steam generator temperature must also be approximately 523 degrees F. Because core heat is being removed by the SGs, the SGs are a saturated system. Therefore, to determine correct SG pressure to obtain 100 degrees F subcooling margin, one must determine the saturation pressure at 523 degrees F, which is approximately 820 psia (which is equal to approximately 805 psig).
✗ A. Plausible if the operator incorrectly calculates the required subcooling temperature or incorrectly reads the Steam Table value.
✗ C. Plausible if the operator fails to convert 820 psia to psig.
✗ D. Plausible if the operator incorrectly calculates the required subcooling temperature or incorrectly reads the Steam Table value.
Ref: ASME Steam Tables | LO: NOS05STEAM0-02 | Source: Modified Bank - INPO GFES Bank P575 | Cognitive: Comprehension/Analysis

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