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@PHDTHESIS{Titov:50677,
      author       = {Titov, Maxim},
      title        = {{C}haracterisation and final disposal behaviour of
                      thoria-based fuel kernels in aqueous phases},
      volume       = {4180},
      issn         = {0944-2952},
      school       = {Techn. Hochsch. Aachen},
      type         = {Dr. (FH)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-50677, Juel-4180},
      series       = {Berichte des Forschungszentrums Jülich},
      pages        = {VII, 143 p.},
      year         = {2005},
      note         = {Record converted from VDB: 12.11.2012; Aachen, Techn.
                      Hochsch., Diss., 2005},
      abstract     = {Two high-temperature reactors (AVR and THTR) operated in
                      Germany have produced about 1 million spent fuel elements.
                      The nuclear fuel in these reactors consists mainly of
                      thorium-uranium mixed oxides, but also pure uranium dioxide
                      and carbide fuels were tested. One of the possible solutions
                      of utilising spent HTR fuel is the direct disposal in deep
                      geological formations. Under such circumstances, the
                      properties of fuel kernels, and especially their leaching
                      behaviour in aqueous phases, have to be investigated for
                      safety assessments of the final repository. In the present
                      work, unirradiated ThO$_{2}$,
                      Th$_{0.906}$,U$_{0.094}$)O$_{2}$,
                      (Th$_{0.834}$,U$_{0.166}$)O$_{2}$ and UO$_{2}$ fuel kernels
                      were investigated. The composition, crystal structure and
                      surface of the kernels were investigated by traditional
                      methods. Furthermore, a new method was developed for testing
                      the mechanical properties of ceramic kernels. The method was
                      successfully used for the examination of mechanical
                      properties of oxide kernels and for monitoring their
                      evolution during contact with aqueous phases.The leaching
                      behaviour of horia-based oxide kernels and powders was
                      investigated in repositoryrelevant salt solutions, as well
                      as in artificial leachates. The influence of different
                      experimental parameters on the kernel leaching stability was
                      investigated. It was shown that thoria-based fuel kernels
                      possess high chemical stability and are indifferent to
                      presence of oxidative and radiolytic species in solution.
                      The dissolution rate of thoria-based materials is typically
                      several orders of magnitude lower than of conventional
                      UO$_{2}$ fuel kernels. The life time of a single intact
                      (Th,U)O$_{2}$ kernel under aggressive conditions of salt
                      repository was estimated as about hundred thousand years.
                      The importance of grain boundary quality on the leaching
                      stability was demonstrated. Numerical Monte Carlo
                      simulations were performed in order to explain the results
                      of leaching experiments.},
      cin          = {ISR},
      cid          = {I:(DE-Juel1)VDB182},
      pnm          = {Nukleare Sicherheitsforschung},
      pid          = {G:(DE-Juel1)FUEK249},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/50677},
}