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@INPROCEEDINGS{Bosbach:138581,
      author       = {Bosbach, Dirk and Brandt, Felix and Klinkenberg, Martina
                      and Rozov, Konstantin and Vinograd, Victor},
      title        = {{R}adium solubility control in the ${B}a{SO}_4$ –
                      ${R}a{SO}_4$ solid-solution aqueous solution system},
      reportid     = {FZJ-2013-04680},
      year         = {2013},
      abstract     = {Radium is a decay product of 238U and 232Th and plays an
                      important role regarding the dose rate in long term safety
                      assessments for the direct disposal of nuclear fuel
                      elements. The solubility control of Ra by the formation of a
                      RaxBa1-xSO4 solid solution has been demonstrated in many
                      cases [1]. Coprecipitation leads to the formation of
                      structurally incorporated Radium within the barite
                      structure. Such solid solutions are ubiquitous in natural
                      systems – most minerals in nature are atomistic mixtures
                      of elements rather than pure compounds. In many cases the
                      formation of solid solutions leads to a thermodynamically
                      more stable situation compared to the formation of pure
                      compounds, due to a negative excess Gibbs energy of mixing.
                      However, radionuclide solubility controlled by solid
                      solutions is currently not considered in long term safety
                      assessments for a nuclear waste repository system. One
                      reason is related to the fact that only a limited number of
                      rather simple solid solution systems have been studied to a
                      sufficient level. Nevertheless, the thermodynamic concepts
                      for solid solution formation under repository relevant
                      conditions are very well developed. Here we have combined
                      microscopic and spectroscopic experimental approaches to
                      study in detail how a Ra containing solution will
                      equilibrate with solid BaSO4 under repository relevant
                      conditions. In combination with atomistic modeling a
                      molecular level mixing model has been derived. In general,
                      Radium solubility is significantly reduced if it is
                      controlled by a binary (Ra,Ba)SO4 solid solution. Atomistic
                      modeling indicates that a regular solid solution model may
                      be applied. The thermodynamic parameters for the solid
                      solution have been derived and can now be applied in the
                      safety assessment of the direct disposal of nuclear fuel
                      elements. Literature: [1] H. A. Doerner, $\&$ W. M. Hoskins,
                      (1925) Journal of the American Chemical Society, 47,
                      662-675},
      month         = {Sep},
      date          = {2013-09-01},
      organization  = {GDCh-Wissenschaftsforum Chemie 2013,
                       Darmstadt (Germany), 1 Sep 2013 - 4 Sep
                       2013},
      subtyp        = {Invited},
      cin          = {IEK-6},
      cid          = {I:(DE-Juel1)IEK-6-20101013},
      pnm          = {142 - Safety Research for Nuclear Waste Disposal (POF2-142)
                      / SKIN - Slow processes in close-to-equilibrium conditions
                      for radionuclides in water/solid systems of relevance to
                      nuclear waste management (269688)},
      pid          = {G:(DE-HGF)POF2-142 / G:(EU-Grant)269688},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/138581},
}