Mass Transfer & Porous Media (MTPM) - Andra

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P/<strong>MTPM</strong>/46Figure 2: Swelling pressure as a function of time for (1) a MX80 bentonite plug and (2) a (MX80bentonite + 30% mass of sand) plug.hydraulic cut-off, occurs between 4 and 8 hours after test start only. For bentonite alone, after 12 daysswelling under 4 MPa water pressure, an apparent asymptotic swelling pressure of 9.5 MPa is reached.Effective asymptotic swelling pressure is evaluated after 19 days, when interstitial water pressure islowered to zero: its value is of 7.2 MPa. Interstitial water pressure is increased to 4 MPa again on day 22,and lowered to zero again on day 27: effective swelling pressure remains at 7.2 MPa. For bentonite+30%sand, apparent swelling pressure is of 8.2 MPa, whereas effective swelling pressure (measured afterlowering interstitial water pressure on day 22) is of 4 MPa only. Therefore, sand addition provides animmediate and full effect of interstitial water pressure variations whereas 100% bentonite is affected ofonly half that pressure (with swelling pressure lowered by 2.3 MPa and not 4 MPa when water pressureis off). This is interpreted as an effect of a higher water retention capacity of 100% bentonite compared tobentonite+30% sand. Water permeability and gas breakthrough pressure are also quantified during thesetests , they confirm the interpretation proposed.References:S. T. Horseman, J. F. Harrington & P. Sellin (1999), “Gas migration in clay barriers", EngineeringGeology, vol. 54.M. Victoria Villar & A. Lloret (2007), “Dismantling of the first section of the FEBEX in situ test: THMlaboratory tests on the bentonite blocks retrieved”, Physics and Chemistry of the Earth, vol.32.J. Graham, K. G. Halayko, H. Hume, T. Kirkham, M. Gray & D. Oscarson (2002), “A capillarity-advectivemodel for gas break-through in clays”, Engineering Geology, vol.64.Page 514INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENT
P/<strong>MTPM</strong>/47SPECIES-SPECIFIC TRANSPORTAND REACTIVE TRANSPORT MODELLINGOF A LONG-TERM CORE INFILTRATIONEXPERIMENT ON OPALINUS CLAYU. Mäder 1 and Th. Gimmi 1,21. Rock-Water Interaction, Institute of Geological Sciences, University of Bern, Baltzerstrasse 1-3,CH-3012 Bern, Switzerland (urs@geo.unibe.ch)2. Laboratory for Waste Management, NES, Paul Scherrer Institut, CH-5232 Villigen, Switzerland(thomas.gimmi@psi.ch)INTRODUCTIONArgillacous rocks have very low hydraulic conductivities, large sorption and ion exchange capacities, andare rather homogeneous. This makes them well suited for deep disposal of radioactive waste. InSwitzerland, Opalinus Clay, a Jurassic marine indurated sediment, is considered as a potential host rockfor high-level radioactive waste. The claystone has been investigated for the past 10 years in the Mont Terriunderground laboratory where it is accessible in a broad anticline of the Jura Mountains.Because of its low permeability of 10 -14 -10 -13 m/s, pore water cannot easily be sampled from Opalinus Clay.Thus, mostly indirect methods are employed in order to characterize the chemical composition of the porewater, notably aqueous extraction followed by geochemical modelling of the data on the basis of themineralogical composition of the rock and ion exchange properties (Pearson et al. 2003). Alternatively,high-pressure squeezing may be applied whereby the rock matrix is deformed.An alternative to destructive methods is the advective displacement of the preserved porewater from a rockcolumn by injecting a synthetic porewater that can be traced to aid in the data interpretation. Thebreakthrough and retardation behaviour of chemical constituents can be examined if such a displacementexperiment is continued. The results from such an experiment are presented whereby pore water of adrillcore sample of Opalinus Clay was advectively displaced by a traced synthetic pore water over morethan 3 years. The objectives were to (1) test and refine this method to obtain little-disturbed samples ofthe original pore water, and (2) measure the breakthrough of multiple tracers for the determination ofspecies-specific transport properties by (reactive) transport modelling. The method was applied to a coresample from the BPC-A1 borehole, and the work is a task of the PC (Porewater Chemistry) Experimentat Mont Terri. Preliminary results and porewater composition was presented by Mäder et al. (2004, andabstract at Tours 2005 meeting).METHODSDrilling parallel to bedding with compressed nitrogen minimized the ingress of oxygen. Sample preparationwas done on site. A drillcore (OD = 79 mm, L = 120 mm) was placed in the infiltration apparatus undera confining pressure of 6.2-7.4 MPa. The porosity of the core as estimated from the water loss of adjacentsamples was 0.165 m 3 m -3 . The temperature was kept at approximate in situ conditions of the formation of13-15°C. A synthetic porewater of similar salinity as the in situ pore water was used. It was traced withbromide, deuterium, and 18 O. The infiltration pressure was created by pressurized He in the head space ofa closed-volume reservoir.The sample effluent was collected under protective He atmosphere and extracted periodically. The sampleswere analysed for chemical constituents (Cl - , Br - , SO 4 2- , Na + , K + , Ca 2+ , Mg 2+ , and others) and for the isotopetracers. The isotope tracers and Br - were used to estimate the degree of mixing between synthetic andoriginal pore water, as well as to estimate the corresponding transport coefficients. These coefficients wereINTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENTPage 515
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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
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 92 and 93: P/MTPM/45Relative concentration / (
Page 96 and 97: P/MTPM/47then used in the transport
Page 98: P/MTPM/4820181614121086Gas pressure
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