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@TECHREPORT{Soler:894811,
      author       = {Soler, Josep M. and Meng, Shuo and Moreno, Luis and
                      Neretnieks, Ivars and Liu, Longcheng and Kekäläinen, Pekka
                      and Hokr, Milan and Říha, Jakub and Vetešník, Aleš and
                      Reimitz, Dan and Višňák, Jakub and Vopálka, Dušan and
                      Kröhn, Klaus-Peter and Tachi, Yukio and Ito, Tsuyoshi and
                      Svensson, Urban and Iraola, Aitor and Trinchero, Paolo and
                      Voutilainen, Mikko and Deissmann, Guido and Bosbach, Dirk
                      and Park, Dong Kyu and Ji, Sung-Hoon and Gvoždík, Libor
                      and Milický, Martin and Polák, Michal and Makedonska,
                      Nataliia and Kuluris, Stephen P. and Karra, Satish and
                      Viswanathan, Hari S. and Gylling, Björn and Lanyon, G.
                      William},
      title        = {{E}valuation report of {T}ask 9{B} based on comparisons and
                      analyses of modelling results for the Äspö {HRL}
                      {LTDE}-{SD} experiments. {T}ask 9 of {SKB} {T}ask {F}orce
                      {GWFTS} – {I}ncreasing the realism in solute transport
                      modelling based on the field experiments {REPRO} and
                      {LTDE}-{SD}},
      volume       = {TR-20-17},
      number       = {TR-20-17},
      address      = {Solna, Sweden},
      publisher    = {Svensk Kärnbränslehantering AB},
      reportid     = {FZJ-2021-03406, TR-20-17},
      series       = {SKB Technical Report},
      pages        = {71 p.},
      year         = {2021},
      abstract     = {Task 9B of the SKB Task Force on Modelling of Groundwater
                      Flow and Transport of Solutes (Task Force GWFTS) was the
                      second subtask within Task 9 and focused on the modelling of
                      experimental results from the LTDE-SD in situ tracer test.
                      The test had been performed at a depth of about 410 m in the
                      Äspö Hard Rock Laboratory. Synthetic groundwater
                      containing a cocktail of radionuclide tracers was circulated
                      for 198 days on the natural surface of a fracture and in a
                      narrow slim hole drilled in unaltered rock matrix.
                      Overcoring of the rock after the end of the test allowed for
                      the measurement of tracer distribution profiles in the rock
                      from the fracture surface (A cores) and also from the slim
                      hole (D cores). The measured tracer activities in the rock
                      samples showed long profiles (several cm) for non- or
                      weakly-sorbing tracers (Cl-36, Na-22), but also for many of
                      the more strongly-sorbing radionuclides. The understanding
                      of this unexpected feature was one of the main motivations
                      for this modelling exercise. However, re-evaluation and
                      revision of the data during the course of Task 9B provided
                      evidence that the anomalous long tails at low activities for
                      strongly sorbing tracers were an artefact due to
                      cross-contamination during rock sample preparation. A few
                      data points remained for Cs-137, Ba-133, Ni-63 and Cd-109,
                      but most measurements at long distances from the tracer
                      source (> 10 mm) were now below the reported detection
                      limits.Ten different modelling teams provided results for
                      this exercise, using different concepts and codes. One
                      additional team provided results related to conceptual
                      development. The tracers that were finally considered were
                      Na-22, Cl-36, Co-57, Ni-63, Ba-133, Cs-137, Cd-109, Ra-226
                      and Np-237. Three main types of models were used: (1)
                      analytical solutions to the transport-retention equations,
                      (2) continuum-porous-medium numerical models, and (3)
                      microstructure-based models accounting for small-scale
                      heterogeneity (i.e. mineral grains, porosities and/or
                      microfracture distributions) and potential centimetre-scale
                      fractures. The modelling by the different teams led to some
                      important conclusions summarised below.Concerning Na-22 and
                      Cl-36, which showed long penetration profiles, tracer
                      profiles within ca 30 mm from the tracer source could be
                      interpreted with transport and retention parameters
                      consistent with those obtained from laboratory-scale
                      experiments. A disturbed zone, with a thickness of about 5
                      mm, could also be identified. This disturbed zone was
                      especially evident in the Cl-36 data. However, some of the
                      measured cores showed rather flat end tails for Na-22, which
                      could not be reproduced by the homogeneous (i.e. constant
                      transport and retention properties) or the
                      continuum-porous-medium models using parameters consistent
                      with those derived from laboratory-scale experiments.
                      Reproduction of those tails by some of the
                      microstructure-based models was performed by implementing
                      fast transport along microfractures and cm-scale
                      fractures.For the rest of the tracers, which were more
                      strongly sorbing, the profiles did not in general extend
                      beyond 10 mm from the tracer source, with only some data
                      points showing measurable activities further into the rock.
                      Overall, the best fits to the measured profiles within a few
                      mm from the tracer source were achieved by the homogeneous
                      models (constant transport and retention parameters with
                      distance), with apparent diffusion coefficients consistent
                      with laboratory-derived experimental results. Good fits were
                      also achieved by models assuming the presence of a disturbed
                      zone with gradually changing parameters. The fact that most
                      data points above detection limits fell within 5 to 8 mm
                      from the tracer source, and the observations from the Cl-36
                      data, suggest the existence of a disturbed zone with a
                      thickness of a few mm and characterised by rather constant
                      transport and retention parameters. The longer profiles for
                      Cl-36 and Na-22 advocate for an undisturbed rock matrix
                      (unaffected by borehole drilling or alteration zones next to
                      fractures) beyond these 5 to 8 mm from the tracer source.
                      Additionally, the flat profile tails observed for some of
                      the Na-22 profiles may point to the effect of microfractures
                      and cm-scale fractures on radionuclide transport.These
                      conclusions could be reached after (1) the re-evaluation and
                      revision of the experimental data (tracer profiles in the
                      rock), and (2) the analysis of the different sets of model
                      results performed by the different teams.(1) The revision of
                      the experimental data led to the dismissal of most of the
                      measurements showing anomalously high activities far from
                      the tracer source (long flat profile tail ends) for the
                      strongly sorbing tracers, as possible contamination
                      mechanisms during sample preparation were identified. As an
                      additional consequence, this discovery highlighted the
                      importance of using blank samples in future tracer transport
                      experiments. Using blank samples together with samples from
                      the test rock sections during preparation and analysis will
                      aid in the detection of potential contamination or
                      background effects.(2) The work performed by the different
                      modelling teams allowed the comparison of many different
                      model concepts, especially in terms of potential zonations
                      of rock properties, such as the presence of a disturbed zone
                      close to the tracer source, the potential effects of micro-
                      and cm-scale fractures, or the implementation of
                      microstructure-based models. An added value was the
                      motivation provided by these exercises to advance in
                      conceptual and numerical model development, which is a key
                      goal of Task 9.},
      cin          = {IEK-6},
      cid          = {I:(DE-Juel1)IEK-6-20101013},
      pnm          = {1411 - Nuclear Waste Disposal (POF4-141)},
      pid          = {G:(DE-HGF)POF4-1411},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)29},
      url          = {https://juser.fz-juelich.de/record/894811},
}