Mass Transfer & Porous Media (MTPM) - Andra

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P/<strong>MTPM</strong>/47then used in the transport modelling of the reactive components. The hydraulic conductivity wasdetermined periodically from the flow rate, hydraulic gradient and sample dimensions.RESULTS AND DISCUSSIONTransport modelling of the Br– and the δ 2 H breakthrough curves: depending on the boundary conditionsused for modelling, the pore diffusion coefficient for δ 2 H ((1.6±0.2) to (2.2±0.4)·10– 10 m 2 s– 1 ) isapproximately 0.6 to 0.9 times the value obtained for HTO in the laboratory and scaled to the in situtemperature, whereas for Br– ((1.9±0.4)·10– 10 m 2 s– 1 ) it is about 1.3 times the laboratory value for Cl– (VanLoon and Soler, 2004). In view of the data and model uncertainties, the differences to the laboratory valuesare considered to be small. For Br–, the anion exclusion effect is confirmed and leads to an earlierbreakthrough (average linear velocity larger by a factor of approximately 1.7) as compared to δ 2 H. Thecolumn Peclet numbers are approximately 7.4 for Br- and 4 for δ 2 H.The evolution of the major cations (Na, Ca, Mg, K) in the effluent over the first 2.5 years: Ca increasesfirst slightly above and later decreases towards the input concentration, whereas Mg seems to increasesteadily towards the input value. The trend for Na is obstructed by a systematic analytical offset after thefirst 1.5 months that is presently being resolved. Preliminary results suggest a similar behaviour as Ca witha maximum breakthrough value after 300-400 days that lies above the input concentration. Finally, K doesnearly remain constant at the input value. At present, full reactive transport modelling of the data isongoing to check whether the observed behaviour can be explained by cation exchange processes coupledwith a small ionic-strength effect, or any additional contribution from the carbonate system by mineraldissolution or precipitation reactions. Also, alternate approaches to reactive transport modelling in ionicmedia are examined by either applying uniform or species-specific effective diffusion coefficients, whileimposing electroneutrality that in turn leads to transport contributions by electro-migration.CONCLUSIONSWhile earlier work (Mäder et al. 2004) demonstrated the feasibility of the method for porewater extraction,this work focussed on the long-term aspects of core infiltration and monitoring multiple tracer and majorcomponent breakthrough behaviour. From the evaluation of the data of the advective displacementexperiment we conclude that the method appears to be affected by relatively few chemical and physicalartefacts, and offers a promising and valuable alternative to in-situ methods (diffusive exchange,extraction) and laboratory methods (diffusive exchange, leaching, squeezing) for the determination of thepore water composition. It is suggested that several other aspects of ionic transport – includingradionuclides – could be addressed by this approach with the objective to obtain parameters that reflect“true” in-situ properties. This would complement costly in-situ experiments and simple and shorter-termlaboratory experiments that are often affected by some experimental artefacts. In particular, the ability toapply a quasi-hydrostatic confining pressure to the samples is counteracting some of the possible effectsof stress release (micro cracks, uncontrolled swelling or shrinking, relaxation).References:Pearson, F.J., Arcos, D., Bath, A., Boisson, J.-Y., Fernández, A.M., Gaebler, H.E., Gaucher, E., Gautschi,A., Griffault, L., Hernan, P., & Waber, H.N. (2003): Mont Terri Project - Geochemistry of Water in theOpalinus Clay Formation at the Mont Terri Rock Laboratory. Reports of the Federal Office for Waterand Geology (FOWG), Geology Series No 5, Bern, Switzerland.Mäder, U.K., Waber, H.N. & Gautschi, A. 2004. New method for porewater extraction from claystone anddetermination of transport properties with results for Opalinus Clay (Switzerland). In: R.B. Wanty &R.R. Seal II (eds), Proceedings of the 11 th International Symposium on Water-Rock Interaction,Saratoga Springs (N.Y.), 445-449, Balkema.Van Loon, L.R, and J.M. Soler, 2004. Diffusion of HTO, 35 Cl–, 125 I– and 22 Na + in Opalinus Clay: Effect ofconfining pressure, sample orientation, sample depth and temperature. PSI Report Nr. 04–03, PaulScherrer Institut, Villigen, Switzerland.Page 516INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENT
P/<strong>MTPM</strong>/48MODELLING GAS INJECTION TESTSIN DEFORMABLE CLAY BUFFERSS. Olivella , E.E. Alonso and D. ArnedoDepartment of Geotechnical Engineering and Geosciences, Universidad Politècnica de Catalunya(UPC)ABSTRACTA significant issue in long term behaviour of clay buffers is its capability to maintain tightness under theexpected generation of gases due to canister corrosion and other phenomena. Current research in thisimportant topic, directly related to the long term safety evaluation of a repository, concentrates inunderstanding the mechanisms of gas transport through a mass of saturated, compacted bentonite, under theconfinement stress provided by the host rock. A large proportion of the experimental research performedconcerns laboratory tests of gas flow through compacted specimens, fully hydrated. They play the role of“point” tests, although, as explained later, they can be hardly interpreted if they are considered in the Cauchysense of a homogeneous, small specimen able to provide fundamental constitutive behaviour. A model hasbeen developed in order to simulate in a continuous approach based on finite elements, the presence ofembedded discontinuities which are able to simulate gas preferential flow paths. The model is described inAlonso et al, (2006) together with applications of different type, including the simulation of gas flow pathformation in heterogeneous fields. Also the large scale test GMT (performed by NAGRA in Grimsel) hasalready been modelled (Olivella and Alonso, 2005). Yet the simulation of laboratory tests has to providemore insight in the gas flow through clays, and probably, improvements of the constitutive model.Horseman and Harrington (1997) have carried out an investigation which includes gas injection tests onsaturated clay to understand the gas flow mechanisms. Injection of gas in the center of a cylindrical samplewhich has sink points in different zones on the external surface.A 3D domain that represents the laboratory test has been considered for simulating the gas injection testsin these cylindrical samples. The simulation is performed using a hydro-mechanical approach whichFigure 1: Gas pressure (MPa), liquid saturation (-) and gas fluxes (m/s) in a finite element simulation ofa gas injection tests. The cylindrical sample is cut through longitudinal and transversal planes forrepresentation.INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENTPage 517
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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
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P/MTPM/201.81.61.41.2upstream compa
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P/MTPM/21490Pressure [bar]0 10 20 3
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Page 48 and 49: P/MTPM/23HA (µg/g)3002001000(a):pH
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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
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Page 88 and 89: P/MTPM/43The available data are con
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Page 92 and 93: P/MTPM/45Relative concentration / (
Page 94 and 95: P/MTPM/46Figure 2: Swelling pressur
Page 98: P/MTPM/4820181614121086Gas pressure
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