Corrosion behavior of alloy 690TT in soluble boron-free PWR primary water using potassium hydroxide as pH control agent

Abstract

Boric acid has been widely used in primary water of pressurized water reactors (PWR) for homogeneous reactivity control. However, dissolving boric acid in primary water has unfavorable safety features

no immediate reactivity control, positive shift of moderator temperature coefficient, acidic and corrosive primary water, and axial offset anomaly (AOA). Due to unfavorable safety features by using boric acid in primary water, a soluble boronfree primary water system provides potential advantages. A pH control agent of soluble boron-free primary water is necessary because pure water becomes mildly acidic. Potassium hydroxide is regarded as a good pH control agent instead of lithium hydroxide. The steam generator tube with the largest surface area in the primary water system is readily exposed to corrosion. Therefore, a corrosion of steam generator tube is a major concern in the management of primary water chemistry. In this dissertation, the corrosion behavior of Alloy 690TT was investigated in soluble boron-free primary water using potassium hydroxide. Corrosion tests were performed for 100, 500, and 1000 hrs with varying pHT 6.9, 7.2, and 7.5. The characterization of oxide films was conducted by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and secondary ion mass spectrometry.