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Dissertation
INFLUENCE OF RARE-EARTH DOPING AND IRRADIATION ON THE DEFECTS AND MICROSTRUCTURE OF URANIUM OXIDE SPENT NUCLEAR FUEL ANALOGUES
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2021
DOI:
https://doi.org/10.7273/000003158
Handle:
https://hdl.handle.net/2376/125124
Abstract
Nuclear power is a large contributor in global electricity generation. Spent nuclear fuel (SNF) may remain hazardous for millions of years. The favored route for disposal is deep underground in geological repository sites. To assess the long-term safety of and viability of SNF storage in repositories, details must be understood about both the interactions of SNF with its surrounding environment, and the influence of defects present within the SNF. Fuel chemistry and defects created during fuel fabrication or during reactor operation have strong effects on the stability of SNF and its dissolution rates. In long time frames, dissolution and radionuclide release is governed by the stability of the UO2 fuel matrix.Uranium oxides were synthesized with rare-earth doping to simulate fission products in SNF. Microstructures and oxide phases were characterized with scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Defects were introduced via oxidation in air, hydrothermal oxidation, and ion irradiation to examine the effects of doping, and measured using Raman spectroscopy. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to determine the oxidation and stoichiometry of doped UO2. High-temperature Raman measurements were used to assess the oxidation of UO2 to UO2+x in undoped and Zr-doped UO2 and supplement TGA. Luminescence signals that arise from certain combinations of excitation wavelength and rare earth elements were investigated, indicating impurities in some precursor materials. In this study, spectral mapping with Raman spectroscopy is demonstrated using defect signatures and luminescence signals. Intricacies and limitations of Raman band fitting, and comparisons using those fits across sample sets are discussed. Suggestions for best practices when collecting, processing and fitting Raman data are offered.
Finally, the effects of doping are investigated in real-world conditions using single-pass flow through (SPFT) dissolution testing at Pacific Northwest National Laboratories (PNNL). The tests replicated oxidizing conditions found at Yucca Mountain, Nevada, which simulate worst-case waste repository conditions. Slower dissolution was recorded in doped samples, reflecting higher resistance to oxidation demonstrated earlier. To conclude, recommendations for future work are made using the findings and methods described in this research.
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Details
- Title
- INFLUENCE OF RARE-EARTH DOPING AND IRRADIATION ON THE DEFECTS AND MICROSTRUCTURE OF URANIUM OXIDE SPENT NUCLEAR FUEL ANALOGUES
- Creators
- Sam Karcher
- Contributors
- John S McCloy (Advisor)David P Field (Advisor)Xiaofeng Guo (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Mechanical and Materials Engineering, School of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 220
- Identifiers
- 99900652004301842
- Language
- English
- Resource Type
- Dissertation