Effect of water chemistry on the oxide film on Alloy 690 during simulated hot functional testing of a pressurised water reactor

Electrochemical impedance spectroscopic measurements to follow the oxidation of Alloy 690 in high-temperature water environments simulating hot functional test (HFT) chemistries are presented and discussed. The thickness and in-depth composition of the formed oxides is estimated by X-ray photoelectron spectroscopy. Kinetic and transport parameters of the oxidation process are estimated by quantitative comparison of the results with the mixed-conduction model for oxide films. Based on the influence of LiOH and H3BO3 concentrations on the parameter values, conclusions for the relationship between HFT water chemistry and the electrical and electrochemical properties of the passive layer on reactor coolant circuit surfaces are drawn.

► Influence of hot functional test chemistry on Alloy 690 oxidation studied by EIS/XPS. ► Increase in LiOH concentration leads to a higher dissolution rate of the oxide. ► Higher boric acid content leads to more efficient passivation of the surface. ► Oxidation parameters estimated by comparison of results to the Mixed-Conduction Model.