Q12 — Loss of VIB VCT Level and Overpressure Protection
000057AA2.13 (3.0)
Given:
• Unit 2 was at 100% Power when a Loss of the 2A 115V Vital Instrument Bus occurred.
• The CRS has entered S2.OP-AB.115-0001, Loss of 2A Vital Instrument Bus.
The following Volume Control Tank (VCT) components and indications have been affected:
• LT-112, VCT Level - Loss of indication and alarms.
• PI-139, VCT Pressure - Loss of indication.
• The VCT makeup system will be unavailable for normal makeup.
The crew has restored normal letdown in accordance with the procedure and has selected 2CV35 to MANUAL FLOW TO VCT.
Complete the following statements:
The 2LT-114 VCT level can be monitored in the control room using the _(1)_. If VCT level continues to rise above 77%, over-pressurization protection of the VCT is provided by _(2)_.
• Unit 2 was at 100% Power when a Loss of the 2A 115V Vital Instrument Bus occurred.
• The CRS has entered S2.OP-AB.115-0001, Loss of 2A Vital Instrument Bus.
The following Volume Control Tank (VCT) components and indications have been affected:
• LT-112, VCT Level - Loss of indication and alarms.
• PI-139, VCT Pressure - Loss of indication.
• The VCT makeup system will be unavailable for normal makeup.
The crew has restored normal letdown in accordance with the procedure and has selected 2CV35 to MANUAL FLOW TO VCT.
Complete the following statements:
The 2LT-114 VCT level can be monitored in the control room using the _(1)_. If VCT level continues to rise above 77%, over-pressurization protection of the VCT is provided by _(2)_.
A. _(1)_ plant computer
_(2)_ LT-114 automatically diverting the 2CV35 to the CVCS HUT
_(2)_ LT-114 automatically diverting the 2CV35 to the CVCS HUT
B. _(1)_ plant computer
_(2)_ 2CV241, VCT relief valve, relieving to the CVCS HUT.
_(2)_ 2CV241, VCT relief valve, relieving to the CVCS HUT.
C. _(1)_ control console
_(2)_ LT-114 automatically diverting the 2CV35 to the CVCS HUT.
_(2)_ LT-114 automatically diverting the 2CV35 to the CVCS HUT.
D. _(1)_ control console
_(2)_ 2CV241, VCT relief valve, relieving to the CVCS HUT.
_(2)_ 2CV241, VCT relief valve, relieving to the CVCS HUT.
▶ Show Answer & Explanation
✗ A. Incorrect. The first part is correct, LT-114 is only available in the control room using the plant computer. The second part is plausible because the LT-114 controller is a separate Hagen Controller located in the instrument racks behind the control room and not on the control console. It could be believed that the LT-114 could still function in automatic control, even with the LT-112 controller in MANUAL FLOW TO VCT on the console. However, either controller in manual will override the auto function of the other, therefore the CV35 valve will not automatically divert to the CVCS HUT between 77 - 87% level.
✓ B. Correct. LT-114 is only available in the control room using the plant computer. LT-114 is also located in Panel 216 in charging pump alley. The VCT is protected by a relief valve 2CV241 which is set to 75 psig and relieves to the CVCS HUT. The AUTO control of the LT-114 Hagen controller will not function in auto with the LT-112 controller in manual.
✗ C. Incorrect. The first part is plausible because the candidate could believe that there is indication for VCT LT-114 Level on the control console. Incorrect as LT-114 is only available in the control room using the plant computer. LT-114 is also located in Panel 216 in charging pump alley. The second part is plausible because the LT-114 controller is a separate Hagen Controller located in the instrument racks behind the control room and not on the control console. It could be believed that the LT-114 could still function in automatic control, even with the LT-112 controller in MANUAL FLOW TO VCT on the console. However, either controller in manual will override the auto function of the other, therefore the CV35 valve will not automatically divert to the CVCS HUT between 77 - 87% level.
✗ D. Incorrect. The first part is plausible because the candidate could believe that there is indication for VCT LT-114 Level on the control console. Incorrect as LT-114 is only available in the control room using the plant computer. LT-114 is also located in Panel 216 in charging pump alley. The second part is correct because the VCT is protected by a relief valve 2CV241 which is set to 75 psig and relieves to the CVCS HUT. The AUTO control of the LT-114 Hagen controller will not function in auto with the LT-112 controller in manual.
Ref: S2.OP-AB.115-0001(Q), Loss of 2A Vital Instrument Bus | LO: N/A | Source: New | Cognitive: Comprehension/Analysis
Connections
- Related systems: CVCS, 115V AC
- Related procedures: AB.115-0001 — Loss of 115V Vital Instrument Bus
- Related exam: 2020 NRC Written Exam