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@INPROCEEDINGS{Brandt:140944,
      author       = {Brandt, Felix and Klinkenberg, Martina and Breuer, Uwe and
                      Rozov, Konstantin and Bosbach, Dirk},
      title        = {{U}ptake of {R}adium during barite recrystallization},
      reportid     = {FZJ-2013-06165},
      year         = {2013},
      abstract     = {In recent safety assessments for the direct disposal of
                      spent nuclear fuel, Ra has been identified as a main
                      contributor to dose after 100,000 years [1]. Due to the
                      likely presence of BaSO4 which is formed by a reaction of Ba
                      present as a fission product and sulfate ubiquitous in
                      ground waters, it is expected that Ra will form a
                      RaxBa1-xSO4 solid solution via recrystallization, which
                      would lower the Ra concentration in solution significantly.
                      However, due to a lack of reliable data, this solid solution
                      system is currently not considered in long term safety
                      assessments for nuclear waste repositories. For instance,
                      the solubility of the pure RaSO4 endmember is not well
                      defined. Furthermore, available literature data for the
                      interaction parameter a0, which describes the non-ideality
                      of the solid solution, vary by about one order of magnitude
                      [2, 3]. The final Ra concentration in solution in this
                      system is extremely sensitive to the amount of barite
                      present, the difference in the solubility products of the
                      end-member phases, and the degree of non-ideality of the
                      solid solution phase. The EU-funded SKIN project
                      investigates slow processes in close-to-equilibrium
                      conditions for radionuclides in water/solid systems of
                      relevance to nuclear waste management. Within the SKIN
                      project we have combined a macroscopic experimental approach
                      with ToF-SIMS and thermodynamic modelling to study in detail
                      how a Ra containing solution will equilibrate with solid
                      BaSO4 under repository relevant conditions. Batch
                      experiments at close to equilibrium conditions show a final
                      Ra concentration which is several orders of magnitude lower
                      than the solubility of pure RaSO4. For the first time, the
                      spatial distribution of Ra and Ba within the recrystallized
                      barite powders - analysed using an ION-TOF TOF-SIMS -
                      confirms the uptake of Ra into the solid. Solid-solution
                      aqueous-solution equilibrium calculations were carried out
                      for the BaSO4 – RaSO4 – H2O system with the GEMS – PSI
                      code [4] in combination with the NAGRA – PSI thermodynamic
                      database [10]. Thermodynamic modelling fits the experimental
                      data best with an interaction parameter a0 = 0.6 and a
                      solubility product KRaSO4 = -10.41.[1] Norrby, S.;
                      Andersson, J.; Dverstorp, B.; Kautsky, F.; Lilja, C.;
                      Sjöblom, R.; Sundström, B.; Toverud, Ö. $\&$ Wingefors,
                      S. SKB 1997[2] Zhu, C. Geochimica et Cosmochimica Acta,
                      2004, 68, 3327-3337[3] Curti, E.; Fujiwara, K.; Iijima, K.;
                      Tits, J.; Cuesta, C.; Kitamura, A.; Glaus, M. $\&$ Müller,
                      W. Geochimica et Cosmochimica Acta, 2010, 74, 3553-3570[4]
                      Wagner, T.; Kulik, D.; Hingerl, F. $\&$ Dmytrieva, S.
                      Canadian Mineralogist, 2012, 50, 701 - 723[5] Hummel, W.;
                      Berner, U.; Curti, E.; Pearson, F. J. $\&$ Thoenen, T.;
                      Nagra technical report 02-16 2002},
      month         = {Oct},
      date          = {2013-10-14},
      organization  = {EURADWASTE ’13, 8th EC Conference on
                       the Management of Radioactive Waste
                       Community Policy and Research on
                       Disposal, Vilnius (Lithuania), 14 Oct
                       2013 - 17 Oct 2013},
      cin          = {IEK-6 / ZEA-3},
      cid          = {I:(DE-Juel1)IEK-6-20101013 / I:(DE-Juel1)ZEA-3-20090406},
      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)24},
      url          = {https://juser.fz-juelich.de/record/140944},
}