Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Chemistry

Supervisor

Dr. David W. Shoesmith & Dr. J. Clara Wren

Abstract

The present management scenario for the permanent disposal of high level nuclear waste in Canada is to seal it in metallic containers and bury it in a deep stable geologic repository. For thick-walled containers radiation fields on the outside of the container would have a negligible influence on container corrosion. However, to overcome fabrication issues and to reduce costs, steel containers with a thin outer copper coating are being designed making a reassessment of the influence of gamma radiation on container corrosion a potential licensing requirement.

The behaviour of Cu in an aerated vapour phase environment in equilibrium with condensed water has been extensively investigated using surface analysis techniques. In Chapter 3, the long-term corrosion behaviour of Cu in a 75 oC/70 %RH environment was investigated. The results show that, while general corrosion of the surface results in a thin layer of corrosion product that does not grow with time, areas of locally condensed water (termed patches) experienced more extensive corrosion. While the thicknesses of the corrosion product layer at these locations increases with time, the aspect ratio (depth of corrosion product to area corroded) is very small.

In Chapter 4, the effects of a low dose rate of g-radiation (0.3 Gy/h) were investigated by analyzing the change in resistance across a Cu wire, and analyzing surfaces of samples exposed to H2O vapour at 75 oC/85 %RH. While the corrosion rate from the Cu wire data indicated that no significant corrosion was detected, surface analysis of the coupons indicated that again, while corrosion of the general surface is minimal, patches exhibit more extensive corrosion. The effect of low-dose radiation on the general corrosion was an initial accelerated rate of surface coverage by corrosion product on the general areas and an increase in the number and size of patches. The overall extent of corrosion in both areas was comparable to the long-term study described in Chapter 3.

In Chapter 5, the effect of [O2] in a humid environment and the effect of a high radiation dose rate (3 kGy/h) in different gas environments on the initial stages of Cu corrosion were investigated. The results showed that initial O2 content affected the rates of nucleation and growth of the oxide. The faster coverage of the surface by corrosion products with irradiation and the increased thickness of corrosion products indicate that high-dose g-radiation increases the initial rate of corrosion.

Chapter 6 addresses the mechanisms of corrosion in general areas and within patches. In both areas corrosion was controlled by a dual layer of Cu2O/CuO. In the general areas the limited amount of available H2O lead to a protective layer. In the patches the greater availability of H2O allowed corrosion to continue.


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