Journal article
Thermodynamics and Chemical Behavior of Uranyl Superoxide at Elevated Temperatures
ACS Materials Au, Vol.2(1), pp.33-44
08/26/2021
DOI: 10.1021/acsmaterialsau.1c00033
Appears in UI Libraries Support Open Access
Abstract
Understanding the alteration mechanisms of UO2-based nuclear fuel has a range of practical implications for both short- and long-term storage of spent fuel rods and environmental ramifications for the mobility of radioactive material at the Chernobyl and Fukushima sites. The major identified alteration phases on the surface of nuclear waste are analogues of schoepite UO3·2H2O, studtite UO2(O2)·4H2O, rutherfordine UO2CO3, and čejkaite Na4UO2(CO3)3. While α-radiolysis has been shown to cause the ingrowth of uranyl peroxide alteration phases, the prevalence of uranyl carbonate phases on solid waste forms has not been mechanistically explained to date, especially since the alteration chemistry is largely affected by the high temperatures of the spent nuclear material. Herein, we demonstrate the first mechanistic link between the formation of the uranyl superoxide (KUPS-1) phase, its reactivity at temperature ranges relevant to the spent nuclear fuel (40-350 °C), and its thermodynamic transformation into a potassium uranyl carbonate mineral phase, agricolaite K4[UO2(CO3)3], using thermogravimetric analysis, calorimetry, vibrational spectroscopy, and powder X-ray diffraction techniques. The thermodynamics data reveal the metastability of the uranyl superoxide KUPS-1 phase through decomposition of the hydrogen peroxide within the solid-state lattice. Increasing the temperature does not result in the breakdown of the superoxide anion bound to the uranyl cation but instead enhances its reactivity in the presence of CO2 gas, resulting in potassium carbonate phases at intermediate temperatures (150 °C) and in uranyl carbonate phases at higher temperatures (350 °C).
Details
- Title: Subtitle
- Thermodynamics and Chemical Behavior of Uranyl Superoxide at Elevated Temperatures
- Creators
- Dmytro V Kravchuk - Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United StatesTori Z Forbes - Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
- Resource Type
- Journal article
- Publication Details
- ACS Materials Au, Vol.2(1), pp.33-44
- DOI
- 10.1021/acsmaterialsau.1c00033
- ISSN
- 2694-2461
- eISSN
- 2694-2461
- Publisher
- American Chemical Society
- Language
- English
- Date published
- 08/26/2021
- Academic Unit
- Civil and Environmental Engineering; Chemistry
- Record Identifier
- 9984217559502771
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