Q28 — CVCS Letdown HX Temp Detector Fails Low / Boron Release
004 A3.06 (3.6)
Given:
• Salem Unit 2 is at 100% power
• 2CC71, Letdown HX Temp Control Valve, is in Auto
Then:
• 2TE-130, temperature detector for 2CC71, fails LOW
Which of the following describes the impact of this failure?
1. Letdown temperature will (1) and the RCS T-avg temperature will (2).
• Salem Unit 2 is at 100% power
• 2CC71, Letdown HX Temp Control Valve, is in Auto
Then:
• 2TE-130, temperature detector for 2CC71, fails LOW
Which of the following describes the impact of this failure?
1. Letdown temperature will (1) and the RCS T-avg temperature will (2).
A. Letdown temperature rises; RCS Tavg lowers.
B. Letdown temperature rises; RCS Tavg rises.
C. Letdown temperature lowers; RCS Tavg rises.
D. Letdown temperature lowers; RCS Tavg lowers.
▶ Show Answer & Explanation
✓ A. Correct. 2TE-130 fails low, causing the controller to see a low temperature signal. 2CC71 goes closed (reduces CCW cooling flow through the letdown HX). With less cooling, letdown HX outlet temperature rises. Hotter letdown water flowing through the mixed bed demineralizers causes boron release into the RCS (boration effect), which lowers Tavg.
✗ B. Incorrect. Letdown temperature does rise (correct part), but higher temperature through the demineralizers releases boron into the RCS, which is a boration effect. Boration inserts negative reactivity, lowering Tavg, not raising it.
✗ C. Incorrect. 2CC71 goes closed (not open) when 2TE-130 fails low, so letdown temperature rises, not lowers. With boron release from higher demineralizer temperatures, Tavg would lower, not rise.
✗ D. Incorrect. 2CC71 goes closed when the temperature detector fails low, so letdown temperature rises, not lowers. The Tavg direction (lowers) is correct due to boration from demineralizer boron release.
Ref: INPO 191007 Demineralizers | Source: Bank - Salem | Cognitive: Comprehension/Analysis
Connections
- Related systems: CVCS
- Related exam: 2023 NRC Written Exam