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  • 1.
    Eriksen, Trygve E
    et al.
    KTH, Superseded Departments, Chemistry.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Diffusion of I, CS, and SR2- in compacted bentonite-anion exclusion and surface diffusion1996Report (Other academic)
  • 2.
    Eriksen, Trygve
    et al.
    KTH, Superseded Departments, Chemistry.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Molera, Mireia
    KTH, Superseded Departments, Chemistry.
    Sorption effects on cation diffusion in compacted bentonite1999In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 54, no 1-2, p. 231-236Article in journal (Refereed)
    Abstract [en]

    Diffusion of Na+. Cs+, Co2+ and Sr2+ in bentonite compacted to a dry density of 1800 kg m(-3) and saturated with groundwaters and aqueous solutions of differing ionic strength have been studied experimentally using the through diffusion technique. Sorption experiments have been carried out under a wide range of pH and concentration of supporting electrolyte. The dependence of the apparent diffusivity of Na+, Cs+ and Sr2+, mainly sorbed by ion exchange, on the sorption intensity is accommodated by a model encompassing diffusion of the sorbed cations within the electrical double layer next to the mineral surface in addition to diffusion in the pore water. The apparent diffusivity of Co2+, sorbed by surface complexation reactions, corresponds to complete immobilization on sorption.

  • 3.
    Jansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Bentonite Erosion, Laboratory Studies2009Report (Other academic)
    Abstract [en]

    This report covers the laboratory studies that have been performed at Nuclear Chemistry, KTH in the project “Bentonite Erosion”. Many of the experiments in this report were performed to support the work of the modelling group and were often relatively simple.

    One of the experiment series was performed to see the impact of gravity and concentration of mono- and di-valent cations. A clay suspension was prepared in a test tube. A net was placed in contact with the suspension, the test tube was filled with solutions of different concentrations and the system was left overnight to settle. The tube was then turned upside down and the behaviour was visually observed. Either the clay suspension fell through the net or stayed on top. By using this method surprisingly sharp determinations of the Critical Coagulation (Flocculation) Concentration (CCC/CFC) could be made. The CCC/CFC of Ca2+ was for sodium montmorillonite determined to be between 1 and 2 mM.

    An artificial fracture was manufactured in order to simulate the real case scenario. The set-up was two Plexiglas slabs separated by 1 mm thick spacers with a bentonite container at one side of the fracture. Water was pumped with a very low flow rate perpendicular to the bentonite container and the water exiting the fracture was sampled and analyzed for colloid content. The bentonite used was treated in different ways. In the first experiment a relatively montmorillonite rich clay was used while in the second bentonite where only the readily soluble minerals had been removed was used.

    Since Plexiglas was used it was possible to visually observe the bentonite dispersing into the fracture. After the compacted bentonite (1,000 kg/m3) had been water saturated the clay had expanded some 12 mm out into the fracture. As the experiment progressed the clay expanded more out into the fracture and seemed to fractionate in two different phases with less material in the outmost phase. A dark rim which was later analyzed to contain mostly feldspar developed at the border between the two phases.

    After 45 weeks the clay had expanded some 20 cm into the fracture. The colloid content in the outlet solution was however stable and less than 200 mg/l. The size of the colloids was however much smaller than that obtained when MX-80 is dispersed in water. The development of the clay profile into the fracture and the colloid content in the outlet solutions were the same in both experiments.

    In one of the fracture experiments the fracture was tilted, inclining some 2–3 degrees with the higher end at the water outlet. A relatively thick gel accumulated at the inlet side of the fracture, i.e. the clay sedimented towards the water flow, clearly showing that gravity plays a big role in this system.

  • 4.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Diffusion of cations in bentonite clay: laboratory and in-situ studies1999Licentiate thesis, comprehensive summary (Other scientific)
  • 5.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Diffusion of Radionuclides in Bentonite Clay: Laboratory and in sity Studies2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis deals with the diffusion of ions in compactedbentonite clay. Laboratory experiments were performed toexamine in detail different processes that affect thediffusion. To demonstrate that the results obtained from thelaboratory investigations are valid under in situ conditions,two different kinds of in situ experiments were performed.

    Laboratory experiments were performed to better understandthe impact of ionic strength on the diffusion of Sr2+ and Cs+ions, which sorb to mineral surfaces primarily by ion exchange.Furthermore, surface related diffusion was examined anddemonstrated to take place for Sr2+ and Cs+ but not for Co2+,which sorbs on mineral surfaces by complexation.

    The diffusion of anions in bentonite clay compacted todifferent dry densities was also investigated. The resultsindicate that anion diffusion in bentonite clay consists of twoprocesses, one fast and another slower. We ascribe the fastdiffusive process to intralayer diffusion and the slow processto diffusion in interparticle water, where anions are to someextent sorbed to edge sites of the montmorillonite.

    Two different types of in situ experiments were performed,CHEMLAB and LOT. CHEMLAB is a borehole laboratory, where cation(Cs+, Sr2+ and Co2+) and anion (I- and TcO4-) diffusionexperiments were performed using groundwater from a fracture inthe borehole. In the LOT experiments cylindrical bentoniteblocks surrounding a central copper rod were placed in a 4 mdeep vertical borehole. The borehole was then sealed and theblocks are left for 1, 5 or>>5 years. When the bentonitewas water saturated the central copper rod is heated tosimulate the temperature increase due to radioactive decay ofthe spent fuel. Bentonite doped with radioactive Cs and Co wasplaced in one of the lower blocks.

    Interestingly, the redox-sensitive pertechnetate ion (TcO4-)which thermodynamically should be reduced and precipitate asTcO2·nH2O, travelled unreduced through the bentonite.However, at some spots in the clay, the Tc activity wasconsiderably higher. We ascribe these activity peaks toiron-containing minerals in the bentonite, by which Tc(VII) hasbeen reduced to Tc(IV) and precipitated. The cations Sr2+, Cs+and Co2+, as well as the anion I-, behaved in the CHEMLABexperiments as expected from laboratory studies.

    Three experiments in the LOT series are completed. The firsttwo diffusion experiments in LOT were less successful, thefirst due to the fact that saturation of the bentonite was notobtained during the experimental period and the radionuclidesdid not move at all. In the second, the uptake of the bentoniteparcel was less successful. Water from the drilling flushedaway large pieces of the top part of the bentonite and thelower part of the test parcel was super-saturated with waterand expanded when released from the rock.

    The activity distribution in the second experiment wasanalysed. The Co2+ profile looked as we had expected, while Cs+had spread more than our calculations indicated. However, thethird experiment was successful from emplacement, watersaturation and heating to uptake. The activity distribution forboth cations was as expected from laboratory studies.

    Altogether the three different types of experiments give auniform picture of radionuclide diffusion in bentonite clay forthe ions investigated.

  • 6.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E.
    KTH, Superseded Departments, Chemistry.
    In situ anion diffusion experiments using radiotracers2004In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 68, no 3-4, p. 183-192Article in journal (Refereed)
    Abstract [en]

    Diffusion experiments in compacted bentonite have been carried out in situ using the borehole laboratory CHEMLAB. The ordinary anion iodide and the redox-sensitive pertechnetate ion have been investigated. In spite of strongly reducing groundwater conditions, technetium was found to diffuse mostly unreduced as TcO4-, although in some spots in the compacted clay, the activity was significantly higher, which may be explained by reduction of some TcO4- by iron-containing minerals in the bentonite. The measured concentration profiles in the clay cannot be accommodated by assuming one single diffusion process. The experimental data are modeled assuming two diffusion paths, intralamellar diffusion and diffusion in external water. The apparent diffusivity for the intralamellar diffusion was found to be 8.6 x 10(-11) m(2) s(-1) for iodide with a capacity factor of 0.1, while the apparent diffusivity for the diffusion in external water was found to be 5 x 10(-14) m(2) s(-1) with alpha = 2.26. The corresponding values for Tc were found to be D-a = 6 x 10(-11) m(2) s(-1), alpha = 0.1 and D-a = 1 x 10(-13) m(2) s(-1), alpha = 0.46, respectively. The diffusion constants and capacity factors obtained in this study are in accordance with data from laboratory experiments.

  • 7.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E
    Anion Diffusion Experiments Using Radiotracers Under Representative Underground ConditionsIn: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009Article in journal (Other academic)
  • 8.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E
    KTH, Superseded Departments, Chemistry.
    CHEMLAB - in situ diffusion experiments using radioactive tracers1998In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 82, p. 153-156Article in journal (Refereed)
    Abstract [en]

    In situ diffusion experiments in bentonite clay have been carried out in the probe CHEMLAB, using the radioactive tracers Co-57, Sr-85 and Cs-134. The measured diffusion profiles for the radionuclides are in good agreement with predicted profiles obtained from modelling based on apparent diffusivities and sorption coefficients obtained in laboratory experiments with corresponding clay density and ground water composition.

  • 9.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Eriksen, Trygve E
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Wold, Susanna
    KTH, Superseded Departments, Chemistry. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    LOT: in situ diffusion experiments using radioactive tracers2003In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 23, no 1-4, p. 77-85Article in journal (Refereed)
    Abstract [en]

    An experiment series at Aspo Hard Rock Laboratory, called "Long Term Test of Buffer Material", LOT, are carried out at Aspo Hard Rock Laboratory to validate models of clay buffer performance at standard KBS-3 repository conditions and to quantify clay buffer alteration processes at adverse conditions. In conjunction with the tests of the bentonite, cation diffusion tests using caesium and cobalt are performed. Each test contains 38 cylindrical blocks of bentonite clay with a hole in the middle which are placed around a copper rod in a vertically drilled hole at a depth of 450 m. In each test, four identical cylindrical bentonite plugs, doped with 1 MBq Co-57 and Cs-134, respectively, are inserted in the fifth block from the bottom. The system was left to be saturated with ground water before heating of the central copper rod started to simulate the thermal activity of radioactive waste. The experiments continued for 14 months before the bentonite blocks were drilled out using over-core drilling technique. The lowest blocks were cut up, sparsely in the outer layer, and in cubic centimeters, big samples closer to where the activity was inserted. All samples were analyzed using a gamma spectrometer to get a three-dimensional picture of the activity distribution. The system was then fitted to a diffusion model to obtain apparent diffusivities for the two cations. The apparent diffusivity for cobalt agrees well with those obtained in other in situ experiments and in laboratory studies, while the value for caesium is lower than expected. This can be due to that the clay was not fully water saturated during the experiment.

  • 10.
    Jansson, Mats
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Molén, Joel
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Kinetic evaluation of sorption and desorption2010In: Adsorption, ISSN 0929-5607, E-ISSN 1572-8757, Vol. 16, no 3, p. 155-159Article in journal (Refereed)
    Abstract [en]

    Sorption is often quantified by a distribution coefficient, K-d, which is the equilibrium ratio between species sorbed to the rock and species in solution. Traditionally K-d-values are determined in batch experiments from equilibrium concentrations. In this work we describe an approach to determine rate constants for sorption and desorption from data obtained in ordinary batch sorption experiments. By varying the surface area to solution volume ratio in experiments where the dynamics for sorption equilibration is monitored, the rate constants (and consequently the K-d-value, which is the quota between forward and backward reactions) can be determined. To demonstrate the method, sorption of strontium to crushed granite was studied. The K-d-value obtained with the kinetic approach was in good agreement with that obtained from equilibrium concentrations.

  • 11. Karnland, O
    et al.
    Sandén, T
    Johannesson, L-E
    Eriksen, Trygve
    KTH, Superseded Departments, Chemistry.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Wold, Susanna
    KTH, Superseded Departments, Chemistry.
    Pedersen, K
    Rosborg, B
    Long term test of buffer material: Final report on the pilot parcels2000Report (Other academic)
  • 12. Kienzier, B.
    et al.
    Vejmelka, P.
    Romer, J.
    Schild, D.
    Jansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Experiences with underground laboratory experiments2006In: Proceedings of the 11th International High Level Radioactive Waste Management Conference, IHLRWM, 2006, Vol. 2006, p. 271-277Conference paper (Refereed)
    Abstract [en]

    Within the scope of a bilateral cooperation a series of Actiniae Migration Experiments were performed by FZK-INE at the Äspo Hard Rock Laboratory in Sweden. Several in-situ experiments investigating the migration of the actinides 241Am, 237Np, 242/244Pu, as well as of 233U and 99Tc were performed in single fractured granite drill cores. These migration experiments were complemented by laboratory investigations. In all experiments, breakthrough of elements having relatively slow retention kinetics such as Np, Tc and U followed the tendency of the inert HTO tracer resulting in an initial breakthrough. Am and Pu was not found in the eluted water. The breakthrough behaviors could not be explained by a simple sorption mechanism. The redox sensitive actinides and Tc are reduced onto the surfaces of the natural fractures. In contrast, U(VI) remains stable and shows little sorption. Natural uranium present in the minerals of the granite was mobilized. The results of the in-situ experiments performed under conditions as close to nature as possible are summarized and some conclusions are drawn relevant for performance assessment.

  • 13. Kienzler, B.
    et al.
    Vejmelka, P.
    Romer, J.
    Fanghanel, E.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Eriksen, T. E.
    Wikberg, P.
    Swedish-German actinide migration experiment at ASPO hard rock laboratory2003In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 61, no 04-jan, p. 219-233Article in journal (Refereed)
    Abstract [en]

    Within the scope of a bilateral cooperation between Svensk Karnbranslehantering (SKB) and Forschungszentrum Karlsruhe, Institut fur Nukleare Entsorgung (FZK-INE), an actinide migration experiment is currently being performed at the Aspo Hard Rock Laboratory (HRL) in Sweden. This paper covers laboratory and in situ investigations on actinide migration in single-fractured granite core samples. For the in situ experiment, the CHEMLAB 2 probe developed by SKB was used. The experimental setup as well as the breakthrough of inert tracers and of the actinides Am, Np and Pu are presented. The breakthrough curves of inert tracers were analyzed to determine hydraulic properties of the fractured samples. Postmortem analyses of the solid samples were performed to characterize the flow path and the sorbed actinides. After cutting the cores, the abraded material was analyzed with respect to sorbed actinides. The slices were scanned optically to visualize the flow path. Effective volumes and inner surface areas were measured. In the experiments, only breakthrough of Np(V) was observed. In each experiment, the recovery of Np(V) was less than or equal to40%. Breakthrough of Am(III) and Pu(IV) as well as of Np(IV) was not observed.

  • 14. Kienzler, Bernhard
    et al.
    Vejmelka, Peter
    Roemer, Juergen
    Schild, Dieter
    Jansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    ACTINIDE MIGRATION IN FRACTURES OF GRANITE HOST ROCK: LABORATORY AND IN SITU INVESTIGATIONS2009In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 165, no 2, p. 223-240Article in journal (Refereed)
    Abstract [en]

    Within the scope of a cooperation between Svensk Karnbranslehantering AB and Forschungszentrum Karlsruhe, Institut fur Nukleare Entsorgung, a series of actinide migration experiments were performed both in the laboratory and at the Aspo Hard Rock Laboratory in Sweden. The objectives of these experiments were to quantify, the sorption of different actinide elements in single fractures of a granite host rock and to investigate the sorption mechanisms. To guarantee the most realistic conditions-as close to nature as possible-in situ experiments were performed in the Chemlab 2 borehole probe. These migration experiments were complemented by laboratory sorption and migration studies. The latter included batch experiments with flat chips of natural material extracted from fracture surfaces to identify the mineral phases relevant to radionuclide sorption by means of autoradiography. Scanning electron microscopy analyses provided information on the composition of sorption-relevant phases and X-ray photoelectron spectroscopy of Np, Tc, and Fe distribution revealed the redox states of these elements. Important mineral phases retaining all actinides and Tc were Fe-bearing phases. From the migration experiments, elution curves of the inert tracer (HTO), Np(V), U(VI), and to a small extent of Tc(VII) were obtained. Americium (III) and plutonium(IV) were not eluted. The mechanisms influencing the migration of the elements Np, U, and Tc depended on redox reactions. It was shown by various independent methods that Np(V) was reduced to the tetravalent state on the fracture surfaces, thus resulting in a pronounced dependence of the recovery on the residence time. Technetium was also retained in the tetravalent state. Elution of natural uranium from the granite drill cores was significant and is discussed in detail.

  • 15.
    Molera, Mireia
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Anion diffusion pathways in bentonite clay compacted to different dry densities2003In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 23, no 1-4, p. 69-76Article in journal (Refereed)
    Abstract [en]

    Diffusion of the anions Cl- and I- in MX-80 compacted bentonite has been studied at different ionic strengths (0.01, 0.1 M NaClO4) and clay density (0.4, 0.8, 1.2, 1.8 g cm(-3)) at the buffered pH of bentonite 8.2 using a through-diffusion technique with measurement of breakthrough curves and concentration profiles in the bentonite. Apparent diffusivities and capacity factors (alpha=epsilon+rhoK(d)) are obtained from diffusion simulations using the computer code ANADIFF. Two diffusion processes, both with density and ionic strength dependent apparent diffusivities and capacity factors, were observed. The diffusion processes observed are ascribed to diffusion in intralayer and interparticle water. The experimental data indicate that intralayer water constitutes the dominating part of water in bentonite compacted to dry the densities 0.4-1.8 g cm(-3) studied in this work.

  • 16.
    Puranen, Anders
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Mats, Jansson
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    A study on the immobilization of selenium oxyanions by H2/Pd(s) in aqueous solution: Confirmation of the one-electron reduction barrier of selenate2010In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 116, no 1-4, p. 16-23Article in journal (Refereed)
    Abstract [en]

    Selenium is a trace element of concern in several geochemical contexts, due to the potentially high mobility of the selenium oxyanions and the narrow range between deficiency and toxicity of the element. For high level nuclear waste repositories the long-lived fission product 79Se has been identified as a potential key dose contributor for the long-term safety. This paper deals with the catalytic effect of Pd(s) on the H2 reduction of selenium oxyanions which was studied experimentally in aqueous solutions containing bicarbonate and chloride. Pd-catalysts and hydrogen have been proposed for the remediation of various groundwater contaminants and can also serve as a model substance for catalytic noble metal inclusions present in spent nuclear fuel. In this study selenite (SeO32) was found to adsorb on Pd. In the presence of hydrogen the rate of selenite removal increased yielding elemental Se. However, no adsorption or reduction of selenate (SeO42) was observed. A simple radiation chemical experiment revealed a notable barrier towards stepwise one-electron reduction of selenate to selenite. This provides an explanation for the lower reactivity of selenate in systems where reductive immobilization of selenite as well as selenate is thermodynamically favorable.

1 - 16 of 16
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