<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "Characterisation of water penetration into polycrystalline UO2"^^ . "In the event of exposure of spent nuclear fuel to groundwater in a final repository, the preferential\r\ndissolution of grain boundaries rather than matrix dissolution would cause a rapid increase of the\r\nsurface area exposed to groundwater, with effects on the mobilisation of radionuclides and on the\r\noverall mechanical stability of the spent fuel pellet. In this respect, a research project has been\r\nlaunched at the Institute for Transuranium Elements (ITU, Karlsruhe, Germany), with the goal of\r\ngaining understanding of the mechanisms of the penetration of water into polycrystalline UO2 under\r\nconditions relevant for final disposal in a geological repository.\r\nAs a first approach to this issue, the study has been initially focused on natural UO2 with well defined\r\ngrain size and morphology. The experiments have then been extended to SIMFUEL, an inactive\r\nanalogue of UO2 fuel containing elements simulating a spent fuel, to assess potential effects\r\nassociated to the presence of fission products. The experiments consisted of static leaching tests on\r\nUO2 fuel pellets using 18O-labelled water. Unlike most of the diffusion studies on UO2, the experiments\r\nin this study were conducted at low temperature (≈ 25°C and 60°C), in order to reproduce the\r\ntemperature range expected in the geological disposal scenario temperatures. To ensure sufficient\r\ncontact time between the solid phase and the solution for penetration to be detectable experiments\r\nlasted 3-9 months. Experiments were carried out initially in oxidising conditions (in air or in N2\r\nglovebox) and thereafter under 10 bar H2 atmosphere, in order to approach conditions more similar to\r\nthe anoxic and reducing environment expected in the final repository. Pre- and post-corrosion surface\r\ncharacterisation was performed by means of scanning electron microscopy (SEM), atomic force\r\nmicroscopy (AFM) and X-ray photoelectron spectrometry (XPS), while solution analysis was\r\nperformed by inductively coupled plasma mass spectrometry (ICP-MS). The penetration of water was\r\nassessed by depth profiling of the tracer 18O using Secondary Ion Mass Spectrometry (SIMS)\r\nmicroscopy. Well-known analytical models were used to fit of the profiles and determine the relevant\r\ndiffusion coefficients.\r\nFor the first time in this study, the chemical diffusion coefficient of oxygen in different UO2+x phases\r\nwas experimentally determined at temperatures below 100°C. The good agreement with extrapolated\r\nliterature data obtained from high-temperature diffusion experiments verifies the viability of the SIMS\r\ndepth profiling method for the determination of diffusion coefficients, even with a diffusion length of\r\ntens of nm. The study has also reported for the first time evidence of the presence of oxygen/water\r\ngrain-boundary diffusivity in polycrystalline UO2 and an estimate of the diffusion coefficient at 25°C is\r\nhere presented. The study has also shown that the possibility to observe grain boundary diffusion by\r\nSIMS depth profiling might depend to a large degree on the grade of surface oxidation of UO2. In\r\ngeneral, all these experimental findings have given an important starting point for the study of water\r\npenetration in the spent fuel.\r\nZusammenfassung\r\nii\r\nCharakterisierung der Penetration von Wassermolekülen in polykristallines UO2\r\nStichwörter: Urandioxid; SIMFUEL; Sekundärionen-Massenspektrometrie; Tiefenprofil; Korrosion;\r\nAuslaugen; chemische Diffusion; Korngrenzendiffusion; Kristallgitter Diffusion;\r\nSauerstoff-Diffusion; Endlagerung; abgebrannte Brennelemente"^^ . "2013" . . . . . . . "Ilaria"^^ . "Marchetti"^^ . "Ilaria Marchetti"^^ . . . . . . "Characterisation of water penetration into polycrystalline UO2 (PDF)"^^ . . . "Thesis_final.pdf"^^ . . . "Characterisation of water penetration into polycrystalline UO2 (Other)"^^ . . . . . . "indexcodes.txt"^^ . . . "Characterisation of water penetration into polycrystalline UO2 (Other)"^^ . . . . . . "lightbox.jpg"^^ . . . "Characterisation of water penetration into polycrystalline UO2 (Other)"^^ . . . . . . "preview.jpg"^^ . . . "Characterisation of water penetration into polycrystalline UO2 (Other)"^^ . . . . . . "medium.jpg"^^ . . . "Characterisation of water penetration into polycrystalline UO2 (Other)"^^ . . . . . . "small.jpg"^^ . . "HTML Summary of #14979 \n\nCharacterisation of water penetration into polycrystalline UO2\n\n" . "text/html" . . . "540 Chemie"@de . "540 Chemistry and allied sciences"@en . .