Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Dr. Jungsook Clara Wren

Abstract

This thesis presents work focusing on the long-term effect of gamma-radiation on aqueous solution kinetics. Ionizing radiation drives the decomposition of water to form both oxidizing (•OH, O2, H2O2) and reducing (•eaq−, •O2−, •H, H2) chemical species. Over time, these radiolysis products can react with dissolved solutes and participate in interfacial reactions. This can lead to significant changes in the eventual solution redox condition, and gas phase composition, and in certain cases result in the formation of solid species. Understanding the long-term solution kinetics for radiolysis systems is particularly important for the improvement of chemistry control and activity transport models, such as those employed in the nuclear power industry.

In order to study the chemical changes induced by exposing these aqueous systems to gamma‑radiation, species in the aqueous, gaseous and solid phases (where applicable) were monitored by a variety of techniques as a function of irradiation time. Chemical kinetics modeling was performed to both validate obtained experimental results, as well as aid in the interpretation of these results. The presence of dissolved solutes was found to impact the steady-state concentrations of the molecular water radiolysis products by competing with them for reaction with radical species. This radical scavenging lowers the rate of removal of the molecular products and allows their concentrations to reach higher levels, however the increase observed relative to pure water is dependent on pH and solute concentration. Redox active solutes that can undergo pseudo-catalytic reaction cycles with the radical species can also significantly affect the concentrations of water radiolysis products without experiencing a significant change in their net speciation.

Irradiation studies with transition metal solutes were shown to generate uniform sized colloidal species in solution. The radiolytic oxidation of soluble ferrous ions to less soluble ferric species leads to the homogeneous condensation of primary particles out of solution. Prolonged irradiation leads to growth at the particle surface, with the final size determined by the steady state balance of redox reactions occurring on the particle surface. Irradiation was also shown to increase the relative metal oxidation rate on a carbon steel coupon in aqueous solutions, with dissolution dominating over oxide growth at low pH. However, the initial presence of dissolved iron suppresses the metal oxidation rate. The deposition of radiolytically produced iron oxide/oxyhydroxide particles contributes to enhanced oxide film growth on these coupon surfaces, effectively decreasing the driving force for ongoing metal oxidation.

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