Dissertation
Interactions of uranium and reactive oxygen species
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2023
DOI: 10.25820/etd.007051
Abstract
Meeting global energy needs requires development of sustainable and affordable power options with minimal carbon footprint. As the world is moving away from traditional fossil-fuel-based energy sources, nuclear power emerges as a promising alternative providing reliable baseload energy without emission of greenhouse gases. While nuclear energy has been integrated in the United States energy grid since the late 1950s, the nuclear industry still faces challenges with the long-term storage and reprocessing of spent nuclear fuel, and legacy waste from the Manhattan project and plutonium production facilities. Such waste forms present a unique chemical challenge due to radiation fields inducing unexpected chemical reactions on the surface of stored materials. Radiolysis products on the surface of either spent nuclear fuel or stored nuclear waste are typically oxidized forms of uranium as peroxide- or carbonate-bearing alteration phases. As a result, there is a critical need to evaluate various mechanisms that lead to the formation of such alteration phases in the back-end of the nuclear fuel cycle, thus addressing potential challenges in the long-term storage or reprocessing efforts.
The objective of my thesis is to explore various synthetic pathways towards uranium alteration phases found on the surface of spent nuclear fuel and nuclear waste via generation or introduction of reactive oxygen species in the presence of hexavalent uranium. I have reported successful synthesis of uranyl peroxide species using: (i) in-situ generation of organic peroxide via autoxidation of benzaldehyde; (ii) photochemical uranyl-mediated H-abstraction in the solid state resulting in uranyl peroxide dimers; (iii/iv) mechanochemical reactivity of U(IV) and U(VI) oxides with solid alkali metal peroxides. Along with uranyl peroxide phases, we managed to (v) isolate the first uranyl superoxide (O2-●) compound that exhibits direct air capture of carbon dioxide, as well as (vi) demonstrate the behavior and thermodynamic stability of this uranyl superoxide material at elevated temperatures. This thesis presents a significant contribution to our understanding of reactions between reactive oxygen species (peroxide O22- and superoxide O2-●) and uranium, which provide a plausible mechanism for the formation of uranium-bearing alteration phases found on real-life samples of spent nuclear fuel and nuclear waste.
Details
- Title: Subtitle
- Interactions of uranium and reactive oxygen species
- Creators
- Dmytro V. Kravchuk
- Contributors
- Tori Z Forbes (Advisor)David F Wiemer (Committee Member)Scott R Daly (Committee Member)Leonard R MacGillivray (Committee Member)Edward G Gillan (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007051
- Number of pages
- xxv, 306 pages
- Copyright
- Copyright 2023 Dmytro V. Kravchuk
- Language
- English
- Date submitted
- 04/24/2023
- Date approved
- 05/24/2023
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 282-306).
- Public Abstract (ETD)
- In our everyday life we are surrounded with things that are manufactured using robust and resistant materials, yet with time and exposure to natural elements, those materials will inevitably deteriorate. For example, every driver will sooner or later notice rusting metal on their car due to continuous contact with water (rain or snow) and changes in temperature. Luckily, rusting iron is not a complex material, which can be chemically treated with ease or replaced due to its abundance. Interestingly, nuclear fuel is also made from precision-machined metal, however, unlike the steel components of the car, nuclear fuel is composed of uranium. When the spent nuclear fuel is taken out of the reactor, the fuel rods are lowered inside water cooling ponds exposing uranium metal to moisture under high temperatures. Similar to rusting iron, such treatment starts corrosion processes on the surface of spent nuclear rods, however, the “rusting” of uranium is significantly accelerated due to the radiation emitted by the nuclear fuel. The corroded uranium materials, or uranium alteration phases, pose challenges during long-term storage or recycling of nuclear fuel because of their unpredictable chemistry. The goal of my thesis is to investigate various chemical methods (exposure to light, exposure to certain solvents, mechanical grinding) to prepare uranium alteration phases and explain the underlying chemistry behind the corrosion of uranium in both spent nuclear fuel and legacy nuclear waste.
- Academic Unit
- Chemistry
- Record Identifier
- 9984425313802771
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