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@INPROCEEDINGS{Brandt:902899,
      author       = {Brandt, Felix and Klinkenberg, Martina and Caes, Sébastien
                      and Poonoosamy, Jenna and Renterghem, Wouter Van and
                      Barthel, Juri and Lemmens, Karel and Bosbach, Dirk and
                      Ferrand, ; Karine},
      title        = {{D}issolution of simplified nuclear waste glass and
                      formation of secondary phases},
      reportid     = {FZJ-2021-04654},
      year         = {2021},
      abstract     = {Immobilization of high-level and intermediate-level nuclear
                      wastes by vitrification in borosilicate glass is a
                      well-established process. There is a consensus between the
                      waste management agencies of many countries and many experts
                      that vitrified nuclear waste should be disposed of in a deep
                      geological waste repository and therefore its long-term
                      behavior needs to be taken into account in safety
                      assessments. In contact with water, borosilicate glass is
                      metastable and dissolves. In static dissolution experiments,
                      often a surface alteration layer (SAL) forms on the
                      dissolving glass, and later sometimes secondary phases form.
                      Based on boron or lithium release rates, commonly three
                      stages of glass dissolution are defined as a function of the
                      reaction progress: (I) initial dissolution, described by a
                      congruent glass dissolution at the highest rate, (II)
                      residual dissolution, characterized by a glass dissolution
                      rate several orders of magnitude lower than the initial one,
                      and (III) resumption of glass alteration with initial rates.
                      Microscopically, the formation of a complex SAL has been
                      identified as a prerequisite for the slower dissolution
                      kinetics of stage II. Stage III is typically observed under
                      specific conditions, i.e., high temperature and/or high pH
                      driven by the uptake of Si and Al into secondary phases.
                      Different glass dissolution models explaining the mechanisms
                      of the SAL formation and rate-limiting steps have been
                      proposed and are still under debate.In this article
                      different aspects of glass dissolution from recent studies
                      in the literature and our own work are discussed with a
                      focus on the microscopic aspects of SAL formation, secondary
                      phase formation and the resumption of glass dissolution.
                      Most of the experiments in the literature were performed
                      under near-neutral pH conditions and at 90 ∘C, following
                      standard procedures, to understand the fundamental
                      mechanisms of glass dissolution. The example of interaction
                      of glass and cementitious materials as discussed here is
                      relevant for safety assessments because most international
                      concepts include cement e.g., as lining, for plugs, or as
                      part of the general construction of the repository. The aim
                      of the investigations presented in this paper was to study
                      the combined effect of hyperalkaline conditions and very
                      high surface area/volume ratios (SA/V=264000m−1) on the
                      dissolution of international simplified glass (ISG) and the
                      formation of secondary phases at 70 ∘C in a synthetic
                      young cement water containing Ca (YCWCa). The new results
                      show that the SA/V ratio is a key parameter for the
                      dissolution rate and for the formation of the altered glass
                      surface and secondary phases. A comparison with similar
                      studies in the literature shows that especially on the
                      microscopic and nanoscale, different SA/V ratios lead to
                      different features on the dissolving glass surface, even
                      though the SA-normalized element release rates appear
                      similar. Zeolite and Ca-silicate-hydrate phases (CSH) were
                      identified and play a key role for the evolution of the
                      solution chemistry. A kinetic dissolution model coupled with
                      precipitation of secondary phases can be applied to relate
                      the amount of dissolved glass to the evolution of the
                      solution's pH.},
      month         = {Nov},
      date          = {2021-11-10},
      organization  = {Interdisciplinary research symposium
                       On the safety of nuclear disposal
                       practices 2021, Berlin, online
                       (Germany), 10 Nov 2021 - 12 Nov 2021},
      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)},
      pid          = {G:(DE-HGF)POF4-1411},
      typ          = {PUB:(DE-HGF)24},
      url          = {https://juser.fz-juelich.de/record/902899},
}