Q12 — MSLI Actuation Conditions
APE 40 AK3.01 (4.2)
Given:
• Unit 2 reactor tripped due to a Main Generator fault
• All immediate actions of 2-EOP-TRIP-1, Reactor Trip or Safety Injection, are complete
• The RO now reports the following plant status:
- RCS Pressure is 1950 psig and lowering
- RCS Tavg is 542 °F and lowering
- PZR Level is 30% and lowering
- Containment Pressure is 5.3 psig and rising
- 21-23 SG Pressures are 895 psig and lowering
- 24 SG Pressure is 810 psig and lowering
- 24 SG Steam Flow is indicating 42% and 21-23 SG Steam Flows are indicating 41%
Based on the above conditions, which ONE of the following completes the statement?
Main Steam Line Isolation actuated due to...
• Unit 2 reactor tripped due to a Main Generator fault
• All immediate actions of 2-EOP-TRIP-1, Reactor Trip or Safety Injection, are complete
• The RO now reports the following plant status:
- RCS Pressure is 1950 psig and lowering
- RCS Tavg is 542 °F and lowering
- PZR Level is 30% and lowering
- Containment Pressure is 5.3 psig and rising
- 21-23 SG Pressures are 895 psig and lowering
- 24 SG Pressure is 810 psig and lowering
- 24 SG Steam Flow is indicating 42% and 21-23 SG Steam Flows are indicating 41%
Based on the above conditions, which ONE of the following completes the statement?
Main Steam Line Isolation actuated due to...
A. high steam flow with low SG pressure.
B. high steam flow with low-low Tavg.
C. Containment Pressure high.
D. SG Pressure ΔP.
▶ Show Answer & Explanation
✓ B. Correct. Based on the given plant conditions, MSLI actuated due to high steam flows (>40%) on 2/4 SGs and low Tavg (≤ 543 °F) on 2/4 Tavg loops.
✗ A. High steam flow setpoint (>40%) has been exceeded, but the low SG pressure of < 600 psig has not been exceeded. Plausible since this is a condition for actuating MSLI.
✗ C. Containment Pressure at 5.3 psig exceeds the Safety Injection setpoint of 4 psig. For a MSLI a high Containment Pressure needs to exceed 15 psig. Plausible since this is a condition for actuating MSLI.
✗ D. This will actuate an SI signal when a high SG differential pressure needs to exceed the setpoint of > 100 psig lower than the other SGs. Plausible because the operator may incorrectly determine that this SI signal also actuates MSLI.
Ref: NOS05FLUNCY | LO: NOS05FLUNCY, Objective 2.K — State those items in the Licensed Operator Fluency List: Steamline Isolations | Source: New | Cognitive: Comprehension/Analysis
Connections
- Related systems: Main Steam
- Related exam: 2022 NRC Written Exam