Oxidation behaviour of zirconium cladding alloys in high temperature high pressure aqueous environments

Abstract

Zirconium alloys are widely employed as fuel cladding materials in the nuclear power industry also in the pressurized water reactors (PWRs). The oxidation behaviour of Zr-based alloys is of crucial importance for the performance and safety of the reactors. The thesis studied the oxidation behaviour of two major types of them. The main goal was to provide mechanistic understanding of their oxidation process in the high temperature aqueous environment and compare their oxidation performance in such environment. The thesis was composed of two parts. In the literature survey part, issues related to Zr cladding alloys, factors affecting their performance and relevant oxidation theories were explored. In the research work part, two major cladding materials were studied in situ by the contact electric resistance (CER) and electrochemical impedance spectroscopy (EIS) techniques. The final oxide thickness was verified ex situ by optical microscopy. The EIS data is modelled by the equivalent circuit modelling method. Results from different techniques were combined for comprehensive evaluation to draw the conclusions. The EIS measurement and equivalent circuit modeling work provided a good approach for evaluating the oxidation resistance of the cladding materials. Their results were shown to be in accordance with the optical microscopy observations.