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Thesis Format

Monograph

Degree

Master of Science

Program

Geology

Supervisor

Moser, Desmond

2nd Supervisor

Noël, James

Co-Supervisor

Abstract

Copper corrosion is of interest to Canada’s Nuclear Waste Management Organization as it relates to their multi-barrier system for nuclear waste disposal in deep geologic repositories. Spent fuel canisters coated with a thin copper layer must persist for up to one million years. Natural copper from the Keweenaw Peninsula in Michigan, USA, has persisted for over 1 billion years and is here characterized to understand copper corrosion over geological time. Copper samples representing three rock types were characterized using optical microscopy, scanning electron microscopy techniques (energy dispersive X-ray spectroscopy and electron backscatter diffraction), and micro-computed X-ray tomography (microCT) to establish a workflow and test suitability for a larger study. Energy dispersive X-ray spectroscopy mapping revealed mineralogy and copper paragenesis. This first application of electron backscatter diffraction showed mm-scale grain size and orientation microstructures such as twins. A 3D microCT model revealed hidden domains of high-density phases (e.g., Ag).

Summary for Lay Audience

The Nuclear Waste Management Organization of Canada has designed technology to isolate spent nuclear fuel underground in deep geologic repositories for up to 1 million years. The plan is to store the used fuel within steel canisters that have been coated with a thin layer of copper to prevent corrosion of the steel. However, laboratory tests at million year time scales are not practical. In order to investigate the corrosion behaviour(s) of copper over geologic timescales, we looked to natural billion year old copper from the Keweenaw Peninsula in Michigan, USA, which has survived, sometimes un-corroded, for 1 billion years. This study examined three samples from three types of deposits in the region using a suite of imaging techniques to better understand the properties that have resulted in the long-term preservation of natural copper. A scanning electron microscope at Western University was used to obtain elemental and crystallographic (structural) information about the samples. A microCT machine was used to X-ray the samples in 3D to show hidden domains of what is believed to be natural silver within the copper. Together, these imaging techniques allow us to investigate multiple properties of the minerals such as grain size, deformation history, elemental composition, and distribution throughout the sample. This information will be useful in further characterization work done in partnership with corrosion chemists at Western University, and to inform design of NWMO’s container coatings to maximize long-term performance.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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