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@INPROCEEDINGS{Thmmler:917163,
      author       = {Thümmler, Robert and Barthel, Juri and Klinkenberg,
                      Martina and Wolf, M. and Kegler, Philip and De Souza, R. and
                      Mayer, Joachim and Bosbach, Dirk and Brandt, Felix},
      title        = {{D}etailed investigation of the microstructure of {UO}2
                      based model systems for spent nuclear fuel},
      reportid     = {FZJ-2023-00395},
      year         = {2022},
      abstract     = {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.},
      month         = {Nov},
      date          = {2022-11-27},
      organization  = {MRS Fall Meeting $\&$ Exhibit, Boston
                       (USA), 27 Nov 2022 - 2 Dec 2022},
      subtyp        = {Other},
      cin          = {IEK-6 / ER-C-2},
      cid          = {I:(DE-Juel1)IEK-6-20101013 / I:(DE-Juel1)ER-C-2-20170209},
      pnm          = {1411 - Nuclear Waste Disposal (POF4-141) / Investigation of
                      the effect of the microstructure upon the oxidative
                      long-term dissolution of uranium dioxide: a fundamental
                      approach including synthesis and corrosion of simplified
                      model systems as well as electron microscopy and atomistic
                      simulation (455439961)},
      pid          = {G:(DE-HGF)POF4-1411 / G:(GEPRIS)455439961},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/917163},
}