Q34 — CCW Thermal Barrier Leak Indications
008000K1.04 (3.3)
Given:
• Unit 2 is at 100% Power.
The RO reports the following console alarms on 2CC1:
• CC HDR ACTIVITY HI.
• SURGE TANK LEVEL HI-LO.
• DISCHARGE FLOW LO.
The crew has entered S2.OP-AB.CC-0001, Component Cooling Abnormality. Based on just the above plant conditions, which ONE of the following is the source of leakage into the Component Cooling System?
• Unit 2 is at 100% Power.
The RO reports the following console alarms on 2CC1:
• CC HDR ACTIVITY HI.
• SURGE TANK LEVEL HI-LO.
• DISCHARGE FLOW LO.
The crew has entered S2.OP-AB.CC-0001, Component Cooling Abnormality. Based on just the above plant conditions, which ONE of the following is the source of leakage into the Component Cooling System?
A. RHR Heat Exchanger.
B. Letdown Heat Exchanger.
C. Thermal Barrier Heat Exchanger.
D. Seal Water Heat Exchanger.
▶ Show Answer & Explanation
✓ C. Correct. A thermal barrier heat exchanger leak would result in high activity in the CCW System, a high CC Surge tank Level, and a subsequent automatic closure of the 2CC131, RCP Thermal Barrier Valve. The "Discharge Flow Lo" alarm is unique to the automatic response of the 2CC131 closure. The Discharge Flow Hi alarm would have occurred first, resulting in the isolation of the thermal barrier and then subsequent Discharge Flow Lo alarm. The Hi alarm was acknowledged and is therefore presently clear.
✗ A. Incorrect. Plausible because the RHR Heat Exchanger is a high pressure in-leakage source to CCW when in service for RCS Cooldown. Incorrect as RHR is out of service at 100%.
✗ B. Incorrect. Plausible because the Letdown Heat Exchanger is a high pressure in-leakage source. Incorrect, because the "Discharge Flow Lo" alarm is indicative of the automatic closure of 2CC131, RCP Thermal Barrier Valve.
✗ D. Incorrect. Plausible because the Seal Water Heat exchanger is cooled by component cooling and the candidate may believe it is a high pressure source. Incorrect as the seal water heat exchanger cools #1 seal leakoff and pressure has been reduced to less than CCW system pressure. Also incorrect as the "Discharge Flow Lo" alarm is indicative of the automatic closure of 2CC131, RCP Thermal Barrier Valve.
Ref: S2.OP-AB.CC-0001(Q), Component Cooling Abnormality and Bases. NOS05CCW000-11 | LO: NOS05CCW000-11, ELO 8 | Source: New | Cognitive: Comprehension
Connections
- Related systems: CCW, RCPs, RHR, CVCS
- Related procedures: AB.CC-0001 — Loss of Component Cooling Water
- Related exam: 2020 NRC Written Exam