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Dissertation
From peroxide to carbonate: the role of radical species in the reactivity of U(VI) alteration phases
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
DOI: 10.25820/etd.008469
Abstract
Nuclear energy is a promising solution for meeting global energy demands in a sustainable manner. However, expanding its commercial use is challenging due to significant obstacles within the nuclear fuel cycle. Unless fuel is reprocessed, the nuclear fuel ‘cycle’ is not a true closed-loop system, but rather used fuel materials are accumulated, and long-term disposal is necessary. Long- term storage solutions, such as deep geological repositories, have been suggested but concerns involving containment integrity and fuel stability persist. In the event of containment failure and inevitable groundwater exposure, water radiolysis and the subsequent formation of various alteration phases, particularly uranyl peroxides and uranyl carbonates, present the risk of radionuclide release into the environment. Ultimately, efficacy of storage and disposal systems are dictated by corrosion processes, however this chemistry is not fully understood. Corrosion processes are fundamentally linked to the presence of ionizing radiation fields, which induce chemical decomposition through radical formation and other pathways and significantly alter material properties. As such, there is a critical need to investigate the role of radical species in the reactivity of U(VI) alteration phases.
The objective of my thesis is to explore interactions between free radical species and U(VI) with the aim of identifying conditions that promote reactivity and the formation of known secondary alteration phases. This is accomplished by first investigating radical species within uranyl peroxide materials, followed by studying the transformation of these phases into uranyl carbonates and finally probing the stability of the uranyl carbonate phases. I have reported evidence of superoxide radical generation in a variety of uranyl peroxide phases. My findings reveal influences of trace metal impurities, uranium isotopic enrichment, sample age, and exposure to radiation on the extent of superoxide formation. Further, I have identified conditions favoring the transformation of uranyl peroxide and uranyl superoxide to uranyl carbonate phases, as well as the reaction kinetics under atmospherically relevant conditions. Finally, I have evaluated the stability of uranyl carbonate phases throughout exposure to gamma-irradiation. This thesis demonstrates the importance of radical species within various alteration phases; moreover, the contents of this thesis are critical for achieving a more complete understanding of the chemistry of used nuclear fuel.
Details
- Title: Subtitle
- From peroxide to carbonate: the role of radical species in the reactivity of U(VI) alteration phases
- Creators
- Sarah K. Scherrer
- Contributors
- Tori Z. Forbes (Advisor)Renée S. Cole (Committee Member)David M. Cwiertny (Committee Member)Scott R. Daly (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2026
- DOI
- 10.25820/etd.008469
- Publisher
- University of Iowa
- Number of pages
- xxix, 226 pages
- Copyright
- Copyright 2026 Sarah Kathryn Scherrer
- Language
- English
- Date submitted
- 04/09/2026
- Description illustrations
- Illustrations, graphs, charts, tables
- Description bibliographic
- Includes bibliographical references (pages 139-156).
- Public Abstract (ETD)
Longstanding and wide-spread reliance on fossil fuels has severely impacted the environment (climate change) and geopolitical sectors (the global energy crisis). To mitigate these effects, there has been a push for implementing low-carbon energy sources, such as nuclear energy. While promising as a clean energy source, nuclear power has its own challenges to overcome, namely safe long-term storage and disposal of used fuel. Challenges arise in fuel disposal for two main reasons: 1) storage vessels degrade over time, and 2) fuel materials are often reactive, especially when breaches in the storage vessel expose the fuel to their surroundings. When this occurs, there is a risk for radioactive materials to enter the environment, potentially exposing animals, humans, etc. to harmful radiation. A significant amount of research has been dedicated to preventing this from occurring, yet most studies do not account for the presence of ionizing radiation. This type of radiation has enough energy to significantly alter materials in ways that are frequently overlooked but could dramatically change the chemistry occurring in the system through formation of long-lived free radicals. The goal of this dissertation is to begin filling this gap in knowledge by studying how free radicals interact with nuclear fuel materials.
- Academic Unit
- Chemistry
- Record Identifier
- 9985177076002771
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