title: Comparative modeling of an in situ diffusion experiment in granite at the Grimsel Test Site.
abstract: An in situ diffusion experiment was performed at the Grimsel Test Site (Switzerland). Several tracers ((3)H as HTO, (22)Na(+), (134)Cs(+), (131)I(-) with stable I(-) as carrier) were continuously circulated through a packed-off borehole and the decrease in tracer concentrations in the liquid phase was monitored for a period of about 2years. Subsequently, the borehole section was overcored and the tracer profiles in the rock analyzed ((3)H, (22)Na(+), (134)Cs(+)). (3)H and (22)Na(+) showed a similar decrease in activity in the circulation system (slightly larger drop for (3)H). The drop in activity for (134)Cs(+) was much more pronounced. Transport distances in the rock were about 20cm for (3)H, 10cm for (22)Na(+), and 1cm for (134)Cs(+). The dataset (except for (131)I(-) because of complete decay at the end of the experiment) was analyzed with different diffusion-sorption models by different teams (IDAEA-CSIC, UJV-Rez, JAEA) using different codes, with the goal of obtaining effective diffusion coefficients (De) and porosity (ϕ) or rock capacity (α) values. From the activity measurements in the rock, it was observed that it was not possible to recover the full tracer activity in the rock (no activity balance when adding the activities in the rock and in the fluid circulation system). A Borehole Disturbed Zone (BDZ) had to be taken into account to fit the experimental observations. The extension of the BDZ (1-2mm) is about the same magnitude than the mean grain size of the quartz and feldspar grains. IDAEA-CSIC and UJV-Rez tried directly to match the results of the in situ experiment, without forcing any laboratory-based parameter values into the models. JAEA conducted a predictive modeling based on laboratory diffusion data and their scaling to in situ conditions. The results from the different codes have been compared, also with results from small-scale laboratory experiments. Outstanding issues to be resolved are the need for a very large capacity factor in the BDZ for (3)H and the difference between apparent diffusion coefficients (Da) from the in situ experiment and out-leaching laboratory tests.
authors.affiliation: IDAEA-CSIC, Jordi Girona 18-26, 08034 Barcelona, Catalonia, Spain. Electronic address: josep.soler@idaea.csic.es.
authors.forename: Josep M
authors.initials: JM
authors.lastname: Soler
authors.affiliation: UJV-Rez, Rez 130, 250 68, Czech Republic.
authors.forename: Jiri
authors.initials: J
authors.lastname: Landa
authors.affiliation: UJV-Rez, Rez 130, 250 68, Czech Republic. Electronic address: hvl@ujv.cz.
authors.forename: Vaclava
authors.initials: V
authors.lastname: Havlova
authors.affiliation: JAEA, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194, Japan. Electronic address: tachi.yukio@jaea.go.jp.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Tachi
authors.affiliation: JAEA, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Ebina
authors.affiliation: Université de Poitiers, HYDRASA/IC2MP 4, rue Michel Brunet - TSA 51106, 86073 Poitiers Cedex 9, France. Electronic address: paul.sardini@univ-poitiers.fr.
authors.forename: Paul
authors.initials: P
authors.lastname: Sardini
authors.affiliation: Laboratory of Radiochemistry, Department of Chemistry, A.I.Virtasen Aukio 1, FIN-00014 University of Helsinki, Helsinki, Finland. Electronic address: marja.siitari-kauppi@helsinki.fi.
authors.forename: Marja
authors.initials: M
authors.lastname: Siitari-Kauppi
authors.affiliation: Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland. Electronic address: jost.eikenberg@psi.ch.
authors.forename: Jost
authors.initials: J
authors.lastname: Eikenberg
authors.affiliation: NAGRA, Hardstrasse 73, Postfach 280, CH-5430 Wettingen, Switzerland. Electronic address: andrew.martin@nagra.ch.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Martin
mesh_terms: D000538:Aluminum Silicates; D002588:Cesium Radioisotopes / Q000032:analysis; D004058:Diffusion; D007457:Iodine Radioisotopes / Q000032:analysis; D008962:Models, Theoretical; D016062:Porosity; D017680:Potassium Compounds; D012822:Silicon Dioxide; D012979:Sodium Radioisotopes / Q000032:analysis; D013557:Switzerland; D014875:Water Pollutants, Radioactive / Q000032:analysis*; D014877:Water Pollution, Chemical / Q000032:analysis
chemical_list: D000538:Aluminum Silicates; D002588:Cesium Radioisotopes; D007457:Iodine Radioisotopes; D017680:Potassium Compounds; D012979:Sodium Radioisotopes; D014875:Water Pollutants, Radioactive; C007886:granite; C016447:feldspar; D012822:Silicon Dioxide
keywords: Diffusion; Granite; Grimsel; Modeling