Mass Transfer & Porous Media (MTPM) - Andra

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P/MTPM/27Relative concentration (C-C1 )/(C0 -C1 )0.31.0σ =1.0Mgm -3 Polarize for 4 hourI=0. 1MConstant current 20 mA 7.9 mmPlane sourceT=298K22 + Nat=21600s0.2V=3. 0×10 -7 ms -1-4.9 mm0.518H OD =3.8×10 -10 hm 2 s - 13 6 -2Cl 4.3 mmConstant current 20 mAE=260V m - 10.1He0.06.5m m0.0-20 -10 0 10 20 30 40-20-1001020Anode (+)x/10 –3 1.9 mmmCathode (-)Anode (+)x / 10 - 3 mFigure 1: Concentration profile of H 2 18 O migrated byelectro-osmosis in water saturated montmorillonite.Relative concentration / (-)Cathode (-)Figure 2: Concentration profiles of H 2 18 O, 22 Na + [1],He [1] and 36 Cl - [2] from plane sources by electromigrationand electro-osmosis.∂ Cxt ( ,) ∂ 2 Cxt ( ,)= D − V ∂ Cxt ( ,)h∂ t ∂ x 2 ∂ x(1)where C ( x , t ) is the concentration at distance, x , from the contact plane and time, t . Hydraulic dispersioncoefficient and advection velocity of H 2 18 O are given by D h and V , respectively. The concentration profilesof Na + and Cl - under electric potential gradient were reported by Higashihara et al. [1] [2]. In order tocompare migration behavior in the montmorillonite among species, especially from the view point ofelectric property, the concentration profiles of H 2 18 O, 22 Na + [1], He [1] and 36 Cl - [2] are shown as advectiondispersionfrom plane source (Fig. 2). The width of the peak corresponds to the hydraulic dispersion.Hydraulic dispersion consists of the two different processes; one is molecular diffusion including sorptionand the other is mechanical dispersion. Therefore, a hydraulic dispersion coefficient D h can be obtainedfrom the sum of a coefficient of mechanical dispersion D m and molecular diffusion coefficient D a .Dh = Da + D m(2)D m is related to the velocity of a chemical species, as follows.Dm = α V(3)where á is the dispersivity parameter of a species and reflects the hydraulic properties of the porousmedium for migration of chemical species. Hydraulic dispersion coefficient of He was definitelylarger than that of H 2 18 O whose dispersion coefficient is slightly larger than that of 36 Cl - , and muchlarger than that of 22 Na + . This fact results from the difference of the dispersivity parameters amongchemical species and implies that electrically positive 22 Na + , negative 36 Cl - and neutral He migrated indifferent paths in water-saturated compacted Na-montmorillonite. The migration paths of the specieswill be discussed.References[1] T. Higashihara, et al., Appl. Clay Sci. 26, 91-98 (2004).[2] T. Higashihara, Migration of Radionuclides and Characteristics of Water in Bentonite Buffer Materialfor Geologic Disposal, A Doctoral Thesis, Hokkaido University (2004).Page 476INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENT
P/MTPM/28DETERMINISTIC AND PROBABILISTICCOMPART-MENTAL MODELLINGOF NITRATE REDUCTION AND TRANSFERIN A BITUMINOUS WASTE CELLAND THE ADJACENT HOST ROCKA. Albrecht 1 , MA. Romero 1 , M. Azaroual 2 , H. Pauwels 2 , L. André 2Andra, Parc de la Croix Blanche, 1/7, rue Jean-Monnet, F-92298 Châtenay-Malabry Cedex( achim.albrecht@andra.fr ; ma.romero@andra.fr)BRGM, 3 Avenue Claude Guillemin, Boite Postale 6009, F-45060 Orléans Cedex 2( h.pauwels@brgm.fr ; m.azaroual@brgm.fr ; l.andre@brgm.fr)INTRODUCTIONThe oxidation state of radionuclides is of general importance to waste management, regardless of wastetype, activity or proposed disposal option. A variety of radionuclides is known to have a higher mobilityin the oxidised form compared to the reduced form. U(VI) vs. U(IV), Se(VI) vs. Se(IV) or Tc (VII) vs.Tc(IV) are well know examples. The oxidation state within the waste remains somewhat uncertain. Thecategory of medium activity long lived waste, called B2 waste at Andra, results from the chemicaltreatment of radionuclides with different reactants, among them nitrates and sulphates. The presence ofnitric acid and the generally oxidising conditions of most waste treatment steps, make an oxidized formfor redox-sensitive radionuclides more likely. The precipitate is stabilised using bitumen and poured intosteel containers. In the Andra Dossier 2005 concept 4 of these primary waste containers are accommodatedby a rectangular cement overpack of which 16 fit into the cross section of a B2 waste cell (Figure 1).After closure of the waste cell, the near-field will slowly start to re-saturate with H 2 O passing through thecement engineered barrier and the overpack and then through the permeable lid of the steel containers tocontact the nitrate - bitumen mixture, but nitrate dissolution initiates only when relative humidity reachesa value of 74%. The presence of nitrates in solution will have a significant impact on the redox conditionsand therefore on the oxidation state of radionuclides released from the waste. Quantifying nitrate reductionand their transport is the main goal of this modelling study. Possible electron donors present in the nearfieldare indicated in Table 1, with Fe 0 as part of the steel container, the two organic molecules representingbitumen and formic acid, the latter an example of the principal bitumen degradation products. Hydrogengas is produced via radiolysis of the bitumen and via anaerobic corrosion of iron with H + as electronacceptor. Extensive research on nitrates in the biosphere indicates the impact of bacteria on reductionreactions with extremely slow kinetic under sterile conditions (Devlin et al., 2000).MODELLING CONCEPTThe behaviour of nitrates within a B2 waste cell is quantified using a 1D compartmental approach, with asource compartment represented by the steel waste container, an interface zone between the latter and thecement overpack, a number of cement compartments representing overpack and engineered barrier, asecond interface zone between cement and the argillite and finally a series of compartments within thegeologic barrier. Inter compartmental fluxes are quantified based on a combined Fickian and mass balanceapproach. Estimation of electron donor and acceptor concentrations within compartments are based onrelevant redox reactions (Tab. 1). Reaction kinetics are considered to be essentially controlled by bacterialrespiration, modelled using maximum kinetics influenced by bacterial growth, reaction thermodynamicsand the reactant and product concentrations (Jin et Bethke, 2005). Bacterial reactions are assumed to occurprincipally in the two interface zones, suppressed in the cement compartments by the high pH and in thepristine argillite by the lack of space. Parameter values controlling diffusion and kinetics remain taggedINTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENTPage 477
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Poster [MTPM]Mass Transfer & Porous
Page 4 and 5:
P/MTPM/1The free energy cost of for
Page 7 and 8: P/MTPM/3DIFFUSION OF IONS IN UNSATU
Page 9: P/MTPM/4POROUS MEDIA CHARACTERIZATI
Page 12 and 13: P/MTPM/5Oxalate ionsQuartzQuartz +P
Page 14 and 15: 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 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 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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