The Nanoscale Microstructure and Mechanics of the Oxide Formed on Zr-2.5Nb Alloy Exposed to High-Temperature Water
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Authors
Shaik, Adil
Date
2024-09-24
Type
thesis
Language
eng
Keyword
Deuterium , Electron energy loss spectroscopy , Finite element analysis , Micropillars , Nanoporosity , NanoSIMS , Nb oxidation state , Zr-alloys
Alternative Title
Abstract
Zr-2.5Nb alloy is used in Canada Deuterium Uranium (CANDU®) reactors as a pressure boundary material for pressure tubes (PT). Understanding the degradation of PT during service is crucial for ensuring the safe and long-term operation of reactors. In this research, a comprehensive characterization of the oxide formed on Zr-2.5Nb alloy in simulated primary water conditions was conducted. This thesis aims to provide insights into the underlying degradation mechanisms in both irradiated and non-irradiated materials. The difference in corrosion resistance between the irradiated and non-irradiated samples is strongly linked to Nb-rich precipitates in α-Zr. Irradiation altered the oxide microstructure,
resulting in sporadically distributed equiaxed-columnar grains with isolated nanopores. Micropillar compression data of the oxide layer revealed that the elastic modulus of the oxide layer is dependent on the nature and type of defects present in the oxide layer. The failure mode in the oxide layer is brittle. Furthermore, the observed failure mode is mixed - intergranular and transgranular - in the oxide. As the exposure time increases, the nanopore density within the oxide layer increases and the defect density at the water-oxide interface is higher than at the metal-oxide interface. These defects are micro- and nanoporosity and microcracks that effectively control the oxidation tendency of Nb in the
oxide layer with +5, +4, +2 and partially oxidized states present in the oxide layer. The deuterium transport through the oxide layer directly correlates with the defect density. The concentration of deuterium is highest at the water-oxide interface and lowest at the metal-oxide interface. This correlates with a change in defect density and Nb oxidation state, which also decreases between these interfaces.
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ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution 4.0 International