This title appears in the Scientific Report :
2022
Detailed investigation of the microstructure of UO2 based model systems for spent nuclear fuel
Detailed investigation of the microstructure of UO2 based model systems for spent nuclear fuel
In safety assessments for the deep geological disposal of high-level nuclear waste, the possibility and results of direct contact between spent nuclear fuel (SNF) and water are considered. In contact with SNF, oxidative species are continuously produced due to the radiation induced hydrolysis of wat...
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Personal Name(s): | Thümmler, Robert (Corresponding author) |
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Barthel, Juri / Klinkenberg, Martina / Wolf, M. / Kegler, Philip / De Souza, R. / Mayer, Joachim / Bosbach, Dirk / Brandt, Felix | |
Contributing Institute: |
Nukleare Entsorgung; IEK-6 Materialwissenschaft u. Werkstofftechnik; ER-C-2 |
Imprint: |
2022
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Conference: | MRS Fall Meeting & Exhibit, Boston (USA), 2022-11-27 - 2022-12-02 |
Document Type: |
Conference Presentation |
Research Program: |
Aufklärung des Einflusses der Mikrostruktur auf die oxidative Langzeitkorrosion von Urandioxid: Ein fundamentaler Ansatz von der Synthese und Korrosion bis hin zur Elektronenmikroskopie und atomistischer Simulation an vereinfachten Modellsystemen Nuclear Waste Disposal |
Publikationsportal JuSER |
In safety assessments for the deep geological disposal of high-level nuclear waste, the possibility and results of direct contact between spent nuclear fuel (SNF) and water are considered. In contact with SNF, oxidative species are continuously produced due to the radiation induced hydrolysis of water, which then corrode the SNF, releasing radionuclides [1]. Radiation induced hydrolysis and oxidative dissolution are relevant for early conditions of deep geological waste disposal - depending on the burn up, for the first 6000 to 8000 years. Oxidative corrosion is typical for metals and unusual for oxide ceramics like UO2. For many ceramics, grain boundary (GB) dissolution is the dominant dissolution mechanism. However, a detailed mechanistic understanding of the role of microstructure in SNF corrosion is still largely absent. The details of the grain boundary structure have to this day been the subject of just a handful of studies [2]. In a previous work, the microstructure of high burnup SNF was studied, documenting the change in microstructure across the fuel pellet with distinct microstructural regions [3]. To gain a deeper understanding of the effects of individual components on the dissolution kinetics of the complex SNF, a study on UO2 model systems is used, with a focus on the microstructure and grain boundaries.In this project, polycrystalline UO2 samples are synthesised using a co-precipitation method. Besides pure UO2, also samples doped with rare earth elements up to a few mass percent are prepared mimicking fission products in SNF [4]. The success of the synthesis is verified by sample density, XRD and SEM. Further extensive microstructure characterization is performed on polished surfaces using EDX, SEM and EBSD. Statistic on grain size, pore size, grain orientation are presented. In the course of the project corrosion experiments will be performed on these samples. For the purpose of a more detailed analysis of GB structure and their reactivity under oxidizing conditions, the focus is placed on coincidence site lattice (CSL) GBs. CSL boundaries have a comparatively simple structure, which is feasible for modeling. However, this choice requires in experiment to first identify specific GBs and second to extract thin samples suitable for the subsequent transmission electron microscopy (TEM) investigation. The first problem is solved by an efficient EBSD scanning approach, where measurements are only taken near grain boundaries. A pole-figure analysis is performed to determine the crystallographic orientation of the grains and the boundary in order to solve the second problem by extracting a cross-section thin foil using focused ion beam milling. Target of the TEM measurements is to determine the atomic structure including oxygen lattice positions, which play a role in the reactivity of the grain boundaries. The results of these experiments are used as input and crosscheck in molecular dynamic simulations. The simulations are performed to understand the driving forces responsible for the stability of specific GBs and the influence of dopants.[1] Shoesmith, D. W., Noel, J. J., Hardie, D., & Ikeda, B. M. (2000). Hydrogen absorption and the lifetime performance of titanium nuclear waste containers. Corros. Rev., 18(4-5), 331-360.[2] Bourasseau, E., Mouret, A., Fantou, P., Iltis, X., Belin, R.C. (2019). Experimental and simulation study of grain boundaries in UO2. J. Nucl. Mater., 517, 286–295.[3] Gerczak, Tyler J., et al. "Restructuring in high burnup UO2 studied using modern electron microscopy." Journal of Nuclear Materials 509 (2018): 245-259.[4] Kegler, P., Klinkenberg, M., Bukaemskiy, A., Murphy, G.L., Deissmann, G., Brandt, F. and Bosbach, D., (2021). Chromium Doped UO2-Based Ceramics: Synthesis and Characterization of Model Materials for Modern Nuclear Fuels. Materials, 14(20), p.6160. |