Mass Transfer & Porous Media (MTPM) - Andra

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P/<strong>MTPM</strong>/45Relative concentration / (-)-10 -5 0 5 10 15 20 250.5anodecathode1.2anodecathode1.0 x 10 –3 kg m –31.0 x 10 –3 kg m –31.2 x 100.4kg m –31.4 x 10 –3 kg m –31.01.2 x 10 –3 kg m –31.4 x 10 –3 kg m –30.30.81.6 x 10 –3 kg m –30.20.60.40.10.20.0-15 -10 -5 0 5 10x / 10 -3 m15 20 250.0-151.6 x 10 –3 kg m –3Figure 1: Dry density dependence of migration of 22 Na and He in compacted montmorillonite under anelectric potential gradient.Relative concentration / (-)The transport numbers were more than 0.9 and don’t depend on the densities of the montmorillonite. Thisfact indicates that Na + ions behave as a dominant species to satisfy the electrically neutral condition duringthe migration of radionuclides in the montmorillonite.References:Nakazawa, T., Takano, M., Nobuhara, A., Torikai, Y., Sato, S., Ohashi, H. (1999): Activation Energies ofDiffusion of Tritium and Electrical Conduction in Water-Saturated Compacted SodiumMontmorillonite: Proc. 7 th Iint. Conf. Radioactive Waste Management and Environmental Remediation-ASME.Higashihara, T., Kinoshita, K., Sato, S., Kozaki, T. (2004): Electromigration of Sodium Ions and Electro-Osmotic Flow in Water-Saturated, Compacted Na-Montmorillonite, Applied Clay Science, 26, 91-98.Page 512INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENT
P/<strong>MTPM</strong>/46SWELLING, TRANSPORTAND GAS THRESHOLD PRESSUREOF A SEALING BENTONITE PLUG:EFFECT OF SAND ADDITIONF. Skoczylas 1 , C. A. Davy 2 , P. Lebon 3 , J.-D. Barnichon 31. LML - Ecole Centrale de Lille, Cité Scientifique, BP48, 59651 Villeneuve d’Ascq, France2. LGIL, Ecole Centrale de Lille, Cité Scientifique, BP48, 59651 Villeneuve d’Ascq, France3 . ANDRA, 1-7 rue Jean Monnet, 92298 Châtenay-Malabry Cedex, FranceINTRODUCTIONCompacted bentonite blocks are privileged candidates for sealing nuclear waste repositories (Horseman etal., 1999). Indeed, when put in place, sodium bentonite swells and thereby ensures proper sealing as in situexperiments prove (Victoria Villar et al.,2006). When dehydrating, sand addition provides resistanceagainst shrinkage and cracking (Graham et al., 2002). Safety assessment of repositories sealing requires tofully identify bentonite swelling pressure and kinetics at given initial compaction and saturation rate.Complementarily, conditions of potential gas release from bentonite sealing plugs need being identified.Therefore, this papers presents an experimental investigation into bentonite swelling pressure and kinetics,and of its gas threshold pressure, when incorporating up to 30% sand in mass.EXPERIMENTAL METHODThe experiment consists of placing a specimeninside a triaxial cell and subject it to bothconfining pressure (Pc) and interstitial gas orliquid upstream and downstream pressures(P i upstream and P i downstream ). The specimen is designedin order to reproduce an interface betweenbentonite and a surrounding material. Its geometryis chosen circular cylindrical in order to ensureuniform loading conditions, see Figure 1. At thebeginning of each test, a pre-compactedunsaturated bentonite (or sand/bentonite) plug issurrounded by an instrumented tube made of aductile material and then let to swell in presence ofwater. The tube is instrumented with four straingauges which provide an evaluation of the pressuresustained by its inner surface, viz. the bentoniteswelling pressure. During all tests, appliedpressure levels are taken as determined byexperimental in situ investigations: 4 MPainterstitial pressure for bentonite and 12 MPaconfinement (also named lithostatic pressure) ofthe whole specimen.Figure 1: Loading sustained by a bentonite (or sand/bentonite) specimen.RESULTS AND ANALYSISSwelling pressures of bentonite and (bentonite+30%sand in mass) are presented as a function of time inFigure 2. The time for bentonite (or bentonite+sand) to come in contact with its surrounding tube, viz.INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENTPage 513
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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
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P/MTPM/7Initial state with glass an
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P/MTPM/8The mesh of the elementary
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P/MTPM/9Moreover, using another sam
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P/MTPM/10Figure 1: Horizontal cross
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P/MTPM/11n t (mol)as received8 10 -
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P/MTPM/1210,9Degree of saturation (
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P/MTPM/13RESULTSFirst, we estimated
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P/MTPM/142.5Energy (M eV)1.6 1.7 1.
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P/MTPM/15C/Co10.90.80.70.60.50.40.3
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P/MTPM/16ModelIrmayvG-M1vG-M2vG-M3T
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P/MTPM/17Figure 1: Experimental HTO
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P/MTPM/18Diffusion experiments were
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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 66 and 67: P/MTPM/32RESULTSResults show that,
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 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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