Q18 — Loss of Secondary Heat Sink / MSLI on High Steam Flow
W E05 EK1.09 (3.6)
Given:
• Unit 2 lost all feedwater, performing EOP-FRHS-1
• SI manually actuated and reset
• 24 SG selected for depressurization
• MSLI on all SGs except 24
• 22MS167 failed to close
• Depressurization rate set too HIGH
What happens and how does the crew continue depressurization?
• Unit 2 lost all feedwater, performing EOP-FRHS-1
• SI manually actuated and reset
• 24 SG selected for depressurization
• MSLI on all SGs except 24
• 22MS167 failed to close
• Depressurization rate set too HIGH
What happens and how does the crew continue depressurization?
A. No effect, MSLI signals blocked when SI reset
B. Hi steam line diff pressure causes MSLI, use atmospheric dumps
C. Hi steam flow with Lo-Lo Tavg causes MSLI, use atmospheric dumps
D. Lo-Lo Tavg (P-12) closes steam dumps, bypass Tavg pushbuttons to continue
▶ Show Answer & Explanation
✓ C. Correct. 100% steam dump causes high steam flows and Lo-Lo Tavg (P-12). P-12 closes steam dumps AND high steam flow with P-12 actuates MSLI closing all MSIVs. No steam dumps available. Continue depressurization via MS10s (atmospheric dumps). MSLI signals for high steam flow CANNOT be blocked.
✗ A. Manually actuating and resetting SI does NOT block MSLI signals. MSLI for high steam flow cannot be blocked.
✗ B. High steamline differential pressure causes SI, not MSLI. The correct MSLI signal is high steam flow coincident with Lo-Lo Tavg.
✗ D. P-12 does close steam dumps, but MSLI also actuates on high steam flow with Lo-Lo Tavg. MSLI signals cannot be blocked or bypassed with pushbuttons.
Ref: 2-EOP-FRHS-1 (R41) | LO: NOS05FRHS00-05, Obj 6.a | Source: New | Cognitive: Comprehension/Analysis
Connections
- Related systems: Main Steam, RPS/SSPS
- Related procedures: EOP-FRHS-1 — Response to Loss of Secondary Heat Sink
- Related exam: 2023 NRC Written Exam