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Thesis Format

Integrated Article

Degree

Master of Science

Program

Chemistry

Supervisor

Dr. Jungsook Clara Wren

Abstract

The Used Fuel Container (UFC) is a key barrier in Canada’s nuclear fuel disposal plan. Understanding the radiation-induced corrosion of the carbon steel (CS) vessel is critical for predicting the long-term integrity of the UFC. Developing a mechanistic understanding of CS corrosion and the effect of solution parameters is essential.

This work investigates the effects of H2O2, the key radiolytic oxidant, on CS corrosion dynamics in small, stagnant solutions. Elementary processes are identified, corrosion rates are calculated, and the effects of H2O2 concentration are investigated. Corrosion was studied by quantifying the concentrations of H2O2, dissolved iron, pH, and surface morphology evolution as a function of time. Results show that corrosion progresses through different kinetic stages and their rates change drastically with solution parameters.

This project improves the fundamental understanding of CS corrosion and will support the development of a high-fidelity corrosion model for CS in the anticipated UFC environments.

Summary for Lay Audience

Carbon steel (CS) is a material commonly used in the nuclear industry, finding use in coolant pipes to containers for used nuclear fuel disposal. Degradation of CS by aqueous corrosion can result in failure of components and lead to costly maintenance. Aqueous corrosion is a process where metal is lost by different electron and atom exchange steps. Corrosion can progress differently depending on the solution environment it is exposed to. Rates of steps involved in corrosion depend on solution properties such as acidity, volume, temperature, and types and quantities of chemicals in the solution. Since material is continuously introduced into the solution, corrosion behaviour can significantly change with time.

In the nuclear industry, radiation can create reactive species like hydrogen peroxide (H2O2) in solution that participate in corrosion. Radiation complicates corrosion and has been shown to promote coupling between different solution reactions. This coupling makes it difficult to predict the corrosion damage in existing corrosion analysis where coupling is not prevalent. To predict corrosion damage over expected lifetime of CS components, a model must be developed which can predict corrosion damage for 100s of years and accounts for coupling of reactions. To generate long term (+100 years) CS corrosion models that include this observed reaction coupling, experiments must be done to calculate rates of chemical reactions.

This work investigates the effects of H2O2 on CS corrosion dynamics in nuclear waste disposal container like environments. H2O2 is the most impactful species for corrosion in radiation environments. From this work, a fundamental understanding of the processes involved in corrosion and how H2O2 participation in corrosion reactions with time is proposed. Then, the effect of solution parameters like initial H2O2 quantity is investigated, and rates of reaction are calculated.

This project improves the fundamental understanding of the reactions in CS corrosion that can be applied to other materials and metals. The understanding of corrosion reactions established in this work can support the development of predictive models for degrading systems.

Creative Commons License

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

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