Q4 — EOP-APPX-7 Reflux Cooling
EPE11 EK1.01 (4.1)
Given:
• Unit 1 is performing 1-EOP-APPX-7, CONTAINMENT SUMP BLOCKAGE.
• ALL RCPs are stopped.
Attempts to establish containment sump recirculation have failed.
1-EOP-APPX-7, Step 43, MAINTAINING RCS HEAT REMOVAL, is in progress.
• The crew is dumping steam to the condensers from the intact SGs.
In accordance with 1-EOP-APPX-7, which ONE of the following is the reason for dumping steam from the intact SGs?
• Unit 1 is performing 1-EOP-APPX-7, CONTAINMENT SUMP BLOCKAGE.
• ALL RCPs are stopped.
Attempts to establish containment sump recirculation have failed.
1-EOP-APPX-7, Step 43, MAINTAINING RCS HEAT REMOVAL, is in progress.
• The crew is dumping steam to the condensers from the intact SGs.
In accordance with 1-EOP-APPX-7, which ONE of the following is the reason for dumping steam from the intact SGs?
A. To prevent a SG tube rupture.
B. To allow time to make-up to the RWST.
C. To raise injection flow provided by ECCS.
D. To promote Core Reflux Cooling.
▶ Show Answer & Explanation
✓ D. Correct. IAW 2-EOP-APPX-7, step 43 bases document, the operator is instructed to maintain heat removal by either use of RHR System or by dumping steam. If the RCS is not full of liquid at this time, it is especially important to keep the secondary system adequately full of water to promote reflux cooling. Reflux cooling is the mechanism by which steam generated in the RCS enters the SG tubes and is condensed by the cold water on the SG secondary side. This liquid then remains in the primary system and promotes cooling.
✗ A. Incorrect. Plausible because the differential temperature between the primary and the secondary sides of the SG tubes would increase the potential for a tube rupture.
✗ B. Incorrect. Plausible since make-up would be something the crew would do to raise level in the RWST, but this is not the reason for performing step 43 in EOP-APPX-7.
✗ C. Incorrect. Plausible because dumping steam will increase the cooling down of the primary and lower primary plant pressure. This in turn will increase flow from the RH pumps and provide more cooling and more water inventory.
Ref: 1-EOP-APPX-7, Rev 2; 1-EOP-APPX-7 Bases for step 43 | LO: NOS05APPX00, Obj 3 — Given any step, caution, or note in the EOP-APPX procedures, describe the basis | Source: Bank — Byron 2019 NRC RO3 (Jan exam) | Cognitive: Fundamental/Memory
Connections
- Related EOPs: EOP-APPX-7 — Containment Sump Blockage
- Related exam: 2022 NRC Written Exam