Mass Transfer & Porous Media (MTPM) - Andra

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P/<strong>MTPM</strong>/32RESULTSResults show that, on one hand, chloride and sulphate concentrations per kg of rock are identical whateverthe solid/liquid ratios and, in the other hand these values are higher than those obtained from radialdiffusion. The discrepancy between the two types of methods suggests the following remarks: (i) the anionsremoved by leaching argillite powder (< 100µm) would not only come from the pore water but also froma second source such as chlorine- or sulphur-bearing minerals, (ii) the contribution of this last source islimited in the radial diffusion method because keeping the rock sample intact (no grounding) prevents thefluid from leaching large reactive mineral surfaces. In addition, it can be mentioned that the radial diffusionmethod also allows the determination of the argillite anion-accessible porosity, necessary for calculatingthe mobile anion concentrations in pore water.For all these reasons, the radial diffusion method was chosen for determining the vertical distribution ofmobile anions from the tunnel down to the lower calcareous aquifer by means of a 250m deep boreholerecently drilled (winter 2006/2007).ReferencesBeaucaire, C, Michelot J.L, Savoye, S. & Cabrera, J. Groundwater characterization and modelling of waterrockequilibria in the argillaceous formation of Tournemire (Aveyron, France). Submitted to AppliedGeochemistry.Savoye, S., Michelot, J.L., Wittebroodt, C. & Altinier, M.V (2006): Contribution of the diffusive exchangemethod to the characterization of pore-water in consolidated argillaceous rocks. Journal of ContaminantHydrology, 86, 87-104.Page 486INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENT
P/<strong>MTPM</strong>/33A CROSS METHOD OF A NANOSCALEMODEL AND MACROSCOPIC DATATO ESTIMATE ANION EFFECTIVEDIFFUSION COEFFICIENT IN ARGILLITEN.Diaz (1) , F. Goutelard (1) ,, P.Turq (2 )1. CEA/DEN/DPC/SECR/L3MR, CEN Saclay, Bâtiment 450 ,91191 Gif-sur-Yvette Cedex2. LI2C Université Pierre et Marie Curie – 4,place Jussieu-Boîte 51 75252 Paris Cedex 05The Callovo-Oxfordian argillite of the Paris Basin has been proposed as a potential host rock for deepradioactive waste. Because of very low measured permeability, diffusion is assumed to be the maintransport mechanism for solute migration. As 36 Cl - , 129 I - , and SeO 2- 3 are considered to be the majorcontributors to the calculated dose rate associated with the long term underground disposal of nuclearwaste, this study will focus on the diffusion of anionic species in clayey materials. Such speciesexperimentally exhibits slower diffusion compared to water due to anionic exclusion arising from thenegatively charged clay surfaces.In such materials, the diffusion behaviour of anionic species is known to be related to the diffusionproperties of the clayey matrix. The aim of this study is to determine the effective diffusion coefficient ofchloride relatively to that of water in argillite at the micrometer scale taking into account the interfacialphenomena in clay due to its negatively charged surface.A finite element COMSOL Multiphysics code is used to model the diffusion of a species in a 2-D porousmedia at the nanometric scale. This model correlates the effective diffusion coefficient of anion relativelyto that of water in clay to a unique pore size, the ionic strength and the counter-ion valency of the poresolution [1].Through-diffusion experiments have been carried out on illite clay equilibrated with KClO 4 solution. Theeffective diffusion coefficient of D 2 O and Cl - , Br - , I - have been measured for ionic strengths from 0.001 to0.1 Mol/L. The pore size distribution is obtained by N 2 adsorption allowing measurements of pore sizeslower than 180 nm where influence of electrical double layers is likely to occur. CEC and zeta potentialhave also been determined. All this data have been used to implement an up-scaling method which takesinto account the scattering of pore sizes of the clay. The parametric study performed with the nanometricmodel showed that the pore size is one of the main factors influencing anionic exclusion [1]. Thegeometrical variability of the clay in terms of pore size distribution is converted to a distribution ofeffective diffusion coefficient which is randomly implemented into the clayey matrix (figure 1).In a second step, the up-scaling method is extended to one argillite sample from the Callovo-Oxfordian.Through-diffusion experiments are combined with 2-D mineralogical mapping of a sample of Callovo-Oxfordian argillite obtained by scanning electron microspopy and LIBS microprobe [2]. The three majorminerals are identified: carbonates, tectosilicates and phyllosilicates. Carbonates and tectosilicates aredescribed as a non porous media and effective diffusion coefficients are distributed all over the identifiedclay mineral (figure 1).INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENTPage 487
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Poster [MTPM]Mass Transfer & Porous
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P/MTPM/1The free energy cost of for
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P/MTPM/3DIFFUSION OF IONS IN UNSATU
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P/MTPM/4POROUS MEDIA CHARACTERIZATI
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P/MTPM/5Oxalate ionsQuartzQuartz +P
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P/MTPM/6borehole was capped with a
Page 16 and 17: P/MTPM/7Initial state with glass an
Page 18 and 19: P/MTPM/8The mesh of the elementary
Page 20 and 21: P/MTPM/9Moreover, using another sam
Page 22 and 23: P/MTPM/10Figure 1: Horizontal cross
Page 24 and 25: P/MTPM/11n t (mol)as received8 10 -
Page 26 and 27: P/MTPM/1210,9Degree of saturation (
Page 28 and 29: P/MTPM/13RESULTSFirst, we estimated
Page 30 and 31: P/MTPM/142.5Energy (M eV)1.6 1.7 1.
Page 32 and 33: P/MTPM/15C/Co10.90.80.70.60.50.40.3
Page 34 and 35: P/MTPM/16ModelIrmayvG-M1vG-M2vG-M3T
Page 36 and 37: P/MTPM/17Figure 1: Experimental HTO
Page 38 and 39: P/MTPM/18Diffusion experiments were
Page 40 and 41: P/MTPM/19Figure 1: Used mesh for co
Page 42 and 43: P/MTPM/201.81.61.41.2upstream compa
Page 44 and 45: P/MTPM/21490Pressure [bar]0 10 20 3
Page 46 and 47: 134P/MTPM/22through-diffusion exper
Page 48 and 49: P/MTPM/23HA (µg/g)3002001000(a):pH
Page 50 and 51: P/MTPM/24through each sample. The p
Page 52 and 53: P/MTPM/25FIRST RESULTSPreliminary c
Page 54 and 55: P/MTPM/26heterogeneous distribution
Page 56 and 57: P/MTPM/27Relative concentration (C-
Page 58 and 59: P/MTPM/280.75m0.25mTable 1: Cross s
Page 60 and 61: P/MTPM/29Figure 1: A. Scheme of the
Page 62 and 63: P/MTPM/30The presented theory is ex
Page 64 and 65: P/MTPM/31Furthermore, Van Loon et a
Page 68 and 69: P/MTPM/33Clay modellingPore size di
Page 70 and 71: P/MTPM/341.60E-11f H2-d total (kg.m
Page 72 and 73: P/MTPM/350.50η R ()0.400.300.200.1
Page 74 and 75: P/MTPM/36200Bq/g1801601401201008060
Page 76 and 77: P/MTPM/37Argilite (ionic strength 0
Page 78 and 79: P/MTPM/38-Samples cored at 12m were
Page 80 and 81: P/MTPM/39APPLICATIONSCORE 2D has be
Page 82 and 83: P/MTPM/40Figure 1: Sketch drawing o
Page 84 and 85: P/MTPM/41Figure 1: Thermal conducti
Page 86 and 87: P/MTPM/42Figure 2: Model of pore st
Page 88 and 89: P/MTPM/43The available data are con
Page 90 and 91: P/MTPM/44Figure 1: Spatial extensio
Page 92 and 93: P/MTPM/45Relative concentration / (
Page 94 and 95: P/MTPM/46Figure 2: Swelling pressur
Page 96 and 97: P/MTPM/47then used in the transport
Page 98: P/MTPM/4820181614121086Gas pressure
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