Ola Karnland - Academia.edu (original) (raw)

Papers by Ola Karnland

MRS Proceedings, 1991

ABSTRACTField heat experiments with kaolinite/smectite clay surrounding heaters in boreholes were... more ABSTRACTField heat experiments with kaolinite/smectite clay surrounding heaters in boreholes were conducted for 0.7 and 4 years with temperatures up to 170-180°C. The short test gave a high degree of water saturation even in the hottest part (> 75 %) and almost no change in physical properties and mineral composition. The long test gave a dry inner zone of claystone, indicating gas formation, and rich precipitation of silica/aluminum compounds and sulphate minerals. Brittleness characterized the hot parts and stiffening occurred also in the colder parts due to precipitation of silica and aluminum.

Engineering Geology, Nov 1, 2000

To study the physical properties of a bentonite buffer, long-term test (LOT) of buffer material w... more To study the physical properties of a bentonite buffer, long-term test (LOT) of buffer material were performed in granitic rock 450 m underground at the Äspö Hard Rock Laboratory (HRL), Oskarshamn, Sweden. The LOT was set up under conditions similar to those in a ...

Physics And Chemistry Of The Earth, Parts A/b/c, 2008

The NAGRA concept for a high level waste repository includes bentonite pellets for backfilling ar... more The NAGRA concept for a high level waste repository includes bentonite pellets for backfilling around the spent nuclear fuel canisters. Pellets have therefore been produced from granulated Wyoming bentonite (Am. Colloid., brand name MX-80), which have been tested as part of NAGRA’s research program with respect to its sealing properties. Two types of pellet material were used, one containing only

Elsevier eBooks, 2017

Abstract In this chapter the functions and requirements of bentonite in a repository for spent nu... more Abstract In this chapter the functions and requirements of bentonite in a repository for spent nuclear fuel are discussed. These requirements concern, for example, swelling pressure, hydraulic conductivity, and diffusion properties. Mineralogy and analysis techniques for determining physicochemical properties are presented. Bentonite properties are discussed and analyzed in detail by introducing the homogeneous mixture model. It is shown that water-saturated bentonite fundamentally is an osmotic system. A multitude of rather different physicochemical aspects can be described with remarkably simple assumptions that follow from the osmotic nature. It is demonstrated that many of the bentonite properties required in the repository for spent nuclear fuel are governed by montmorillonite interlayers.

Physics And Chemistry Of The Earth, Parts A/b/c, 2007

In the present work, the effect of homogenization on the microstructure and exclusion of chloride... more In the present work, the effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite was studied. The experiments were performed with MX-80 bentonite, from which easily dissolving components, e.g. chlorides and gypsum, had been removed to ensure that the excess ions in the pore water came from the external solution alone. In the first case, the

Geochimica et Cosmochimica Acta, 2012

We present molecular dynamics simulations of the Donnan equilibrium principle in compacted montmo... more We present molecular dynamics simulations of the Donnan equilibrium principle in compacted montmorillonite with three hydration layers of water in the interlayer. This draws attention to the misconception, frequently seen in the literature, stating that anions cannot enter interlayer space due to electrostatic repulsion forces, sometimes referred to as anion exclusion. However, the calculations presented here show that excess salt, i.e., both anions and cations enter interlayer space to the extent predicted by Donnan equilibrium. Thus the excess salt concentration is reduced in the interlayer in comparison to the external electrolyte but not totally excluded.

Physics And Chemistry Of The Earth, Parts A/b/c, 2004

The concentrations caused by the external solution into the porewater were studied with compacted... more The concentrations caused by the external solution into the porewater were studied with compacted bentonite (MX-80), from which easily dissolving components had been removed in order to ensure that the ions in the porewater came from the external solution. The dry densities of the samples varied from 700 to 1700 kg/m3 and NaCl solutions of 0.1–3 M were used as

Physics And Chemistry Of The Earth, Parts A/b/c, 2007

The estimated quantity of cement for construction and sealing purposes is around 9E5 kg in the pl... more The estimated quantity of cement for construction and sealing purposes is around 9E5 kg in the planned Swedish KBS3 repository for nuclear waste. The highly alkaline cement pore fluid (pH > 12) may affect other components in the repository, and especially the bentonite buffer is of concern. In this study, we simulated possible interactions between cement and bentonite by contacting highly compacted bentonite with high molar hydroxide solutions in a series of laboratory experiments. Wyoming bentonite (MX-80) and purified homo-ionic Na-and Ca-montmorillonite were used for tests with 0.1, 0.3 and 1.0 M NaOH, and saturated Ca(OH) 2 solutions. Pressure cells with permeable filters were loaded with compacted discs of bentonite at the proposed buffer density (2000 kg/m 3 at full water saturation). A hydroxide solution was circulated on one side of the cell and an isotonic chloride solution on the other during a minimum of 45 days. Swelling pressure and solution pH were monitored during the tests and the change in the solution composition and bentonite mineralogy were determined after completed tests. No effect on swelling pressure was observed in tests with 0.1 M NaOH (pH 12.9) or saturated Ca(OH) 2 solutions (pH 12.4) and the mineralogical/chemical changes of the clay were minimal. The bentonite swelling pressure was significantly reduced in the tests with 0.3 (pH 13.3) and 1.0 M (pH 13.8) NaOH solutions. The reduction seems to be due to an instant osmotic effect, and to a continuous dissolution of silica minerals, resulting in mass loss and, consequently, a decrease in density. At these high pH, the release of silica was dominating and the CEC of the clay increased by 20-25%. The structural formula of the smectite and X-ray diffraction tests for nonexpandability (Greene-Kelly test) provided strong evidence that the dissolution of montmorillonite proceeds incongruently through an initial step of beidellitization. The calculated rate of silica release from montmorillonite is 1.6EÀ9 g g À1 clay s À1 for 1.0 M and 5EÀ10 g g À1 clay s À1 for 0.3 M NaOH solutions. The Si release rate is, however, not a straightforward measure of the montmorillonite dissolution rate due to the non-stoichiometric dissolution. Upon contact between bentonite and NaCl solutions, ion-equilibrium is established between the external solution and the exchangeable cations of the clay. A similar initial pressure response on exposure of bentonite to NaOH solutions indicates that such equilibrium may establish also with an external NaOH solution. If so, the OH-concentration of the clay pore water will be lower than that of the external solution, which would explain that dissolution rates in our experiments with highly compacted bentonite are lower than those reported for batch experiments with hydroxide solutions of the same concentration.

Physics And Chemistry Of The Earth, Parts A/b/c, 2011

Geological Repository Systems for Safe Disposal of Spent Nuclear Fuels and Radioactive Waste, 2017

Abstract In this chapter the functions and requirements of bentonite in a repository for spent nu... more Abstract In this chapter the functions and requirements of bentonite in a repository for spent nuclear fuel are discussed. These requirements concern, for example, swelling pressure, hydraulic conductivity, and diffusion properties. Mineralogy and analysis techniques for determining physicochemical properties are presented. Bentonite properties are discussed and analyzed in detail by introducing the homogeneous mixture model. It is shown that water-saturated bentonite fundamentally is an osmotic system. A multitude of rather different physicochemical aspects can be described with remarkably simple assumptions that follow from the osmotic nature. It is demonstrated that many of the bentonite properties required in the repository for spent nuclear fuel are governed by montmorillonite interlayers.

Physics And Chemistry Of The Earth, Parts A/b/c, 2007

Decision in Principle to choose Olkiluoto in the municipality of Eurajoki as the site of the fina... more Decision in Principle to choose Olkiluoto in the municipality of Eurajoki as the site of the final disposal facility for spent nuclear fuel. A positive decision was made at the end of 2000 by the Government. The Finnish Parliament ratified the decision in May 2001. The decision makes it possible for Posiva to focus the confirming bedrock investigations at Olkiluoto, where in the next few years an underground rock characterisation facility, ONKALO, will be constructed. As a part of the investigations Suomen Malmi Oy (Smoy) core drilled 401.42 m and 45.60 m deep boreholes with a diameter of 75.7 mm at Olkiluoto in May-June 2006. The identification numbers of the boreholes are OL-KR41 and OL-KR41B, respectively. A set of monitoring measurements and samplings from the drilling and returning water was carried out during the drilling. Both the volume and the electric conductivity of the drilling water and the returning water were recorded. The drill rig was computer controlled and during drilling the computer recorded drilling parameters. The objective of all these measurements was to obtain more information about bedrock and groundwater properties. Sodium fluorescein was used as a label agent in the drilling water. The total volumes of the used drilling and flushing water were 232m 3 and 16.9 m 3 in boreholes OL-KR41 and OL-KR41B, respectively. Measured volume of the returning water was 243m 3 in borehole OL-KR41. The deviation of the boreholes was measured with the deviation measuring instruments EMS and Maxibor. Uniaxial compressive strength, Young's Modulus and Poisson' s ratio were measured from the core samples. The average uniaxial compressive strength is about 101 MPa, the average Young's Modulus is 41 GPa and the average Poisson's ratio is 0.18. The main rock types are veined gneiss, diatexitic gneiss, tonalitic-granodioriticgranitic gneiss and pegmatite granite. The average fracture frequency is 1.1 pes/m in borehole OL-KR41 and 2.9 pes/m in borehole OL-KR41B. The average RQD values were 98.4 o/o and 94.7 o/o. In borehole OL-KR41 three fractured zones and in borehole OL-KR41B one fractured zone were penetrated during drilling work.

Engineering Geology, Oct 1, 1997

This paper describes an application of a technique developed for modeling chemical processes in b... more This paper describes an application of a technique developed for modeling chemical processes in buffer materials that are controlled by a reaction rate and by the transport of one component, which is essential for the process in question to occur. The application described here is the illitization of smectite by fixation of potassium ions in cation exchange positions. and with diffusion of dissolved potassium being the transport process. The technique is verified by comparison with analytical solutions. An overview, based on small models, is given which outlines under what constellations of assumptions the time scale for conversion of the buffer is controlled by reaction rate parameters and under which conditions transport controls this time scale. Examples are given of calculations performed for deposition holes, with potassium being supplied from the surroundings to the upper parts of the highly compacted bentonite buffer. It is concluded that restrictions in nearfield transport capacity have a very significant effect on the conversion time scale. Towards the end of the heating period about 98% of the smectite is found to remain, even for reaction rates and buffer transport conditions that would have left only 10% of the smectite unconverted without nearfield transport restrictions. It is also concluded that the modeling technique can be applied to other, similar, transport/conversion processes.

Steel components are unstable in EBS environments. They will corrode to fairly insol uble corrosi... more Steel components are unstable in EBS environments. They will corrode to fairly insol uble corrosion products, such as magnetite, and also react with the smectitic matrix of the bentonite buffer. In this study, the impact of reduced iron on the buffer's stability has been assessed within the framework of the KBS-H concept. Our work includes two parts. In the first part, available data from experimental and modelling studies have been compiled and interpreted. In the second part, a relatively simple geochemical modelling exercise on the iron-bentonite interaction in the current KBS-3H disposal system has been performed using Olkiluoto as test case. The iron in this case stems from the perforated supercontainer steel shell foreseen to be emplaced around the buffer material. För att minska på osäkerheten av superbehållarens stålhöljes inverkan på buffertens stabilitet bör noggranna experimentella Fe-bentonitstudier under välkontrollerade syrefria förhållanden utföras. Dessa bör också omfatta mätningar av bufferetns fysikaliska egenskaper. Studierna bör också omfatta diffusionsstudier med Fe(II). Mera avancerade geokemiska modelleringar (t ex också beaktande av multikomponenteffekter) skulle leda till en mera realistisk beskrivning av den den reaktiva järnfronten i bufferten.

Engineering Geology, 1996

There is convincing evidence from field data that smectite clay undergoes conversion primarily to... more There is convincing evidence from field data that smectite clay undergoes conversion primarily to illite and chlorite if it is fully water-saturated and heated. The conversion may take place through mixed-layer formation with increasing illite/smectite ratio at higher temperatures and pressures. This process requires dehydration of the interlamellar space, for which either an external pressure or drying are needed. An alternative mechanism that takes place without dehydration, is dissolution of smectite and neoformation of illite. Both processes imply reorganization of the smectite crystal lattice for which the activation energy is fairly high, meaning that the conversion is negligible at temperatures lower than about 60°C. At elevated temperatures the conversion rate is controlled by the access to potassium for either mechanism. An ongoing detailed investigation of this subject has led to a tentative model for the smectite-to-illite conversion in natural sediments and in canister-embedding clay in high-level radioactive waste (HLW) repositories.

Geochimica et Cosmochimica Acta, Apr 1, 2009

Bentonite clay is proposed as buffer material in several concepts of High Level Radioactive Waste... more Bentonite clay is proposed as buffer material in several concepts of High Level Radioactive Waste repositories, and a correct description of ion diffusion in this material is of vital importance for any quantification of the chemical evolution of the repository near field. This study investigates the importance of ion equilibrium between montmorillonite interlayer space and an external solution for the diffusional behavior of bentonite. Two distinct and well established mechanisms govern this type of ion equilibrium: Donnan equilibrium and ion exchange equilibrium. Donnan equilibrium influences both cations and anions in a symmetric manner, while ion exchange only is relevant in systems of more than one type of cations. Both mechanisms generate ion concentration discontinuities across the bentonite/external solution interface. A general theoretical framework for describing through-diffusion is developed. An expression for the effective diffusion coefficient, D e , is derived, taking into account also the influence of filters typically present in these types of experiments D e ¼ / c N 1 2 þ 1 D c ; where / c is total clay porosity, D c is the diffusion coefficient in the clay, 1 describes the influence of filters and N is a general ion equilibrium coefficient. The above expression is valid for both cations and anions. The theory has been applied to one laboratory study concerning cation (Na +) and two independent laboratory studies concerning anion (Cl À) diffusion in Na-bentonite. The commonly observed different transport behavior for anions and cations in bentonite is principally explained by the concentration discontinuities: N is large for tracer cations at low electrolyte concentrations, but approaches zero for anions in the same concentration limit. The presented theory implies that effective diffusion coefficients evaluated from tracer through-diffusion experiments do not describe diffusive mass transfer in bentonite in general. Furthermore, it shows that ion diffusion in compacted bentonite is principally explained without the commonly used concepts of anion porosity and sorption mechanisms. The striking explanatory power of this basic approach shows the necessity to consider interlayer ion equilibrium in compacted bentonite, and that these considerations must be at the core of any type of modeling (transport, pore water chemistry, mechanics etc.) of bentonite exerting swelling pressure.

MRS Proceedings, 1991

ABSTRACTField heat experiments with kaolinite/smectite clay surrounding heaters in boreholes were... more ABSTRACTField heat experiments with kaolinite/smectite clay surrounding heaters in boreholes were conducted for 0.7 and 4 years with temperatures up to 170-180°C. The short test gave a high degree of water saturation even in the hottest part (> 75 %) and almost no change in physical properties and mineral composition. The long test gave a dry inner zone of claystone, indicating gas formation, and rich precipitation of silica/aluminum compounds and sulphate minerals. Brittleness characterized the hot parts and stiffening occurred also in the colder parts due to precipitation of silica and aluminum.

Engineering Geology, Nov 1, 2000

To study the physical properties of a bentonite buffer, long-term test (LOT) of buffer material w... more To study the physical properties of a bentonite buffer, long-term test (LOT) of buffer material were performed in granitic rock 450 m underground at the Äspö Hard Rock Laboratory (HRL), Oskarshamn, Sweden. The LOT was set up under conditions similar to those in a ...

Physics And Chemistry Of The Earth, Parts A/b/c, 2008

The NAGRA concept for a high level waste repository includes bentonite pellets for backfilling ar... more The NAGRA concept for a high level waste repository includes bentonite pellets for backfilling around the spent nuclear fuel canisters. Pellets have therefore been produced from granulated Wyoming bentonite (Am. Colloid., brand name MX-80), which have been tested as part of NAGRA’s research program with respect to its sealing properties. Two types of pellet material were used, one containing only

Elsevier eBooks, 2017

Abstract In this chapter the functions and requirements of bentonite in a repository for spent nu... more Abstract In this chapter the functions and requirements of bentonite in a repository for spent nuclear fuel are discussed. These requirements concern, for example, swelling pressure, hydraulic conductivity, and diffusion properties. Mineralogy and analysis techniques for determining physicochemical properties are presented. Bentonite properties are discussed and analyzed in detail by introducing the homogeneous mixture model. It is shown that water-saturated bentonite fundamentally is an osmotic system. A multitude of rather different physicochemical aspects can be described with remarkably simple assumptions that follow from the osmotic nature. It is demonstrated that many of the bentonite properties required in the repository for spent nuclear fuel are governed by montmorillonite interlayers.

Physics And Chemistry Of The Earth, Parts A/b/c, 2007

In the present work, the effect of homogenization on the microstructure and exclusion of chloride... more In the present work, the effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite was studied. The experiments were performed with MX-80 bentonite, from which easily dissolving components, e.g. chlorides and gypsum, had been removed to ensure that the excess ions in the pore water came from the external solution alone. In the first case, the

Geochimica et Cosmochimica Acta, 2012

We present molecular dynamics simulations of the Donnan equilibrium principle in compacted montmo... more We present molecular dynamics simulations of the Donnan equilibrium principle in compacted montmorillonite with three hydration layers of water in the interlayer. This draws attention to the misconception, frequently seen in the literature, stating that anions cannot enter interlayer space due to electrostatic repulsion forces, sometimes referred to as anion exclusion. However, the calculations presented here show that excess salt, i.e., both anions and cations enter interlayer space to the extent predicted by Donnan equilibrium. Thus the excess salt concentration is reduced in the interlayer in comparison to the external electrolyte but not totally excluded.

Physics And Chemistry Of The Earth, Parts A/b/c, 2004

The concentrations caused by the external solution into the porewater were studied with compacted... more The concentrations caused by the external solution into the porewater were studied with compacted bentonite (MX-80), from which easily dissolving components had been removed in order to ensure that the ions in the porewater came from the external solution. The dry densities of the samples varied from 700 to 1700 kg/m3 and NaCl solutions of 0.1–3 M were used as

Physics And Chemistry Of The Earth, Parts A/b/c, 2007

The estimated quantity of cement for construction and sealing purposes is around 9E5 kg in the pl... more The estimated quantity of cement for construction and sealing purposes is around 9E5 kg in the planned Swedish KBS3 repository for nuclear waste. The highly alkaline cement pore fluid (pH > 12) may affect other components in the repository, and especially the bentonite buffer is of concern. In this study, we simulated possible interactions between cement and bentonite by contacting highly compacted bentonite with high molar hydroxide solutions in a series of laboratory experiments. Wyoming bentonite (MX-80) and purified homo-ionic Na-and Ca-montmorillonite were used for tests with 0.1, 0.3 and 1.0 M NaOH, and saturated Ca(OH) 2 solutions. Pressure cells with permeable filters were loaded with compacted discs of bentonite at the proposed buffer density (2000 kg/m 3 at full water saturation). A hydroxide solution was circulated on one side of the cell and an isotonic chloride solution on the other during a minimum of 45 days. Swelling pressure and solution pH were monitored during the tests and the change in the solution composition and bentonite mineralogy were determined after completed tests. No effect on swelling pressure was observed in tests with 0.1 M NaOH (pH 12.9) or saturated Ca(OH) 2 solutions (pH 12.4) and the mineralogical/chemical changes of the clay were minimal. The bentonite swelling pressure was significantly reduced in the tests with 0.3 (pH 13.3) and 1.0 M (pH 13.8) NaOH solutions. The reduction seems to be due to an instant osmotic effect, and to a continuous dissolution of silica minerals, resulting in mass loss and, consequently, a decrease in density. At these high pH, the release of silica was dominating and the CEC of the clay increased by 20-25%. The structural formula of the smectite and X-ray diffraction tests for nonexpandability (Greene-Kelly test) provided strong evidence that the dissolution of montmorillonite proceeds incongruently through an initial step of beidellitization. The calculated rate of silica release from montmorillonite is 1.6EÀ9 g g À1 clay s À1 for 1.0 M and 5EÀ10 g g À1 clay s À1 for 0.3 M NaOH solutions. The Si release rate is, however, not a straightforward measure of the montmorillonite dissolution rate due to the non-stoichiometric dissolution. Upon contact between bentonite and NaCl solutions, ion-equilibrium is established between the external solution and the exchangeable cations of the clay. A similar initial pressure response on exposure of bentonite to NaOH solutions indicates that such equilibrium may establish also with an external NaOH solution. If so, the OH-concentration of the clay pore water will be lower than that of the external solution, which would explain that dissolution rates in our experiments with highly compacted bentonite are lower than those reported for batch experiments with hydroxide solutions of the same concentration.

Physics And Chemistry Of The Earth, Parts A/b/c, 2011

Geological Repository Systems for Safe Disposal of Spent Nuclear Fuels and Radioactive Waste, 2017

Abstract In this chapter the functions and requirements of bentonite in a repository for spent nu... more Abstract In this chapter the functions and requirements of bentonite in a repository for spent nuclear fuel are discussed. These requirements concern, for example, swelling pressure, hydraulic conductivity, and diffusion properties. Mineralogy and analysis techniques for determining physicochemical properties are presented. Bentonite properties are discussed and analyzed in detail by introducing the homogeneous mixture model. It is shown that water-saturated bentonite fundamentally is an osmotic system. A multitude of rather different physicochemical aspects can be described with remarkably simple assumptions that follow from the osmotic nature. It is demonstrated that many of the bentonite properties required in the repository for spent nuclear fuel are governed by montmorillonite interlayers.

Physics And Chemistry Of The Earth, Parts A/b/c, 2007

Decision in Principle to choose Olkiluoto in the municipality of Eurajoki as the site of the fina... more Decision in Principle to choose Olkiluoto in the municipality of Eurajoki as the site of the final disposal facility for spent nuclear fuel. A positive decision was made at the end of 2000 by the Government. The Finnish Parliament ratified the decision in May 2001. The decision makes it possible for Posiva to focus the confirming bedrock investigations at Olkiluoto, where in the next few years an underground rock characterisation facility, ONKALO, will be constructed. As a part of the investigations Suomen Malmi Oy (Smoy) core drilled 401.42 m and 45.60 m deep boreholes with a diameter of 75.7 mm at Olkiluoto in May-June 2006. The identification numbers of the boreholes are OL-KR41 and OL-KR41B, respectively. A set of monitoring measurements and samplings from the drilling and returning water was carried out during the drilling. Both the volume and the electric conductivity of the drilling water and the returning water were recorded. The drill rig was computer controlled and during drilling the computer recorded drilling parameters. The objective of all these measurements was to obtain more information about bedrock and groundwater properties. Sodium fluorescein was used as a label agent in the drilling water. The total volumes of the used drilling and flushing water were 232m 3 and 16.9 m 3 in boreholes OL-KR41 and OL-KR41B, respectively. Measured volume of the returning water was 243m 3 in borehole OL-KR41. The deviation of the boreholes was measured with the deviation measuring instruments EMS and Maxibor. Uniaxial compressive strength, Young's Modulus and Poisson' s ratio were measured from the core samples. The average uniaxial compressive strength is about 101 MPa, the average Young's Modulus is 41 GPa and the average Poisson's ratio is 0.18. The main rock types are veined gneiss, diatexitic gneiss, tonalitic-granodioriticgranitic gneiss and pegmatite granite. The average fracture frequency is 1.1 pes/m in borehole OL-KR41 and 2.9 pes/m in borehole OL-KR41B. The average RQD values were 98.4 o/o and 94.7 o/o. In borehole OL-KR41 three fractured zones and in borehole OL-KR41B one fractured zone were penetrated during drilling work.

Engineering Geology, Oct 1, 1997

This paper describes an application of a technique developed for modeling chemical processes in b... more This paper describes an application of a technique developed for modeling chemical processes in buffer materials that are controlled by a reaction rate and by the transport of one component, which is essential for the process in question to occur. The application described here is the illitization of smectite by fixation of potassium ions in cation exchange positions. and with diffusion of dissolved potassium being the transport process. The technique is verified by comparison with analytical solutions. An overview, based on small models, is given which outlines under what constellations of assumptions the time scale for conversion of the buffer is controlled by reaction rate parameters and under which conditions transport controls this time scale. Examples are given of calculations performed for deposition holes, with potassium being supplied from the surroundings to the upper parts of the highly compacted bentonite buffer. It is concluded that restrictions in nearfield transport capacity have a very significant effect on the conversion time scale. Towards the end of the heating period about 98% of the smectite is found to remain, even for reaction rates and buffer transport conditions that would have left only 10% of the smectite unconverted without nearfield transport restrictions. It is also concluded that the modeling technique can be applied to other, similar, transport/conversion processes.

Steel components are unstable in EBS environments. They will corrode to fairly insol uble corrosi... more Steel components are unstable in EBS environments. They will corrode to fairly insol uble corrosion products, such as magnetite, and also react with the smectitic matrix of the bentonite buffer. In this study, the impact of reduced iron on the buffer's stability has been assessed within the framework of the KBS-H concept. Our work includes two parts. In the first part, available data from experimental and modelling studies have been compiled and interpreted. In the second part, a relatively simple geochemical modelling exercise on the iron-bentonite interaction in the current KBS-3H disposal system has been performed using Olkiluoto as test case. The iron in this case stems from the perforated supercontainer steel shell foreseen to be emplaced around the buffer material. För att minska på osäkerheten av superbehållarens stålhöljes inverkan på buffertens stabilitet bör noggranna experimentella Fe-bentonitstudier under välkontrollerade syrefria förhållanden utföras. Dessa bör också omfatta mätningar av bufferetns fysikaliska egenskaper. Studierna bör också omfatta diffusionsstudier med Fe(II). Mera avancerade geokemiska modelleringar (t ex också beaktande av multikomponenteffekter) skulle leda till en mera realistisk beskrivning av den den reaktiva järnfronten i bufferten.

Engineering Geology, 1996

There is convincing evidence from field data that smectite clay undergoes conversion primarily to... more There is convincing evidence from field data that smectite clay undergoes conversion primarily to illite and chlorite if it is fully water-saturated and heated. The conversion may take place through mixed-layer formation with increasing illite/smectite ratio at higher temperatures and pressures. This process requires dehydration of the interlamellar space, for which either an external pressure or drying are needed. An alternative mechanism that takes place without dehydration, is dissolution of smectite and neoformation of illite. Both processes imply reorganization of the smectite crystal lattice for which the activation energy is fairly high, meaning that the conversion is negligible at temperatures lower than about 60°C. At elevated temperatures the conversion rate is controlled by the access to potassium for either mechanism. An ongoing detailed investigation of this subject has led to a tentative model for the smectite-to-illite conversion in natural sediments and in canister-embedding clay in high-level radioactive waste (HLW) repositories.

Geochimica et Cosmochimica Acta, Apr 1, 2009

Bentonite clay is proposed as buffer material in several concepts of High Level Radioactive Waste... more Bentonite clay is proposed as buffer material in several concepts of High Level Radioactive Waste repositories, and a correct description of ion diffusion in this material is of vital importance for any quantification of the chemical evolution of the repository near field. This study investigates the importance of ion equilibrium between montmorillonite interlayer space and an external solution for the diffusional behavior of bentonite. Two distinct and well established mechanisms govern this type of ion equilibrium: Donnan equilibrium and ion exchange equilibrium. Donnan equilibrium influences both cations and anions in a symmetric manner, while ion exchange only is relevant in systems of more than one type of cations. Both mechanisms generate ion concentration discontinuities across the bentonite/external solution interface. A general theoretical framework for describing through-diffusion is developed. An expression for the effective diffusion coefficient, D e , is derived, taking into account also the influence of filters typically present in these types of experiments D e ¼ / c N 1 2 þ 1 D c ; where / c is total clay porosity, D c is the diffusion coefficient in the clay, 1 describes the influence of filters and N is a general ion equilibrium coefficient. The above expression is valid for both cations and anions. The theory has been applied to one laboratory study concerning cation (Na +) and two independent laboratory studies concerning anion (Cl À) diffusion in Na-bentonite. The commonly observed different transport behavior for anions and cations in bentonite is principally explained by the concentration discontinuities: N is large for tracer cations at low electrolyte concentrations, but approaches zero for anions in the same concentration limit. The presented theory implies that effective diffusion coefficients evaluated from tracer through-diffusion experiments do not describe diffusive mass transfer in bentonite in general. Furthermore, it shows that ion diffusion in compacted bentonite is principally explained without the commonly used concepts of anion porosity and sorption mechanisms. The striking explanatory power of this basic approach shows the necessity to consider interlayer ion equilibrium in compacted bentonite, and that these considerations must be at the core of any type of modeling (transport, pore water chemistry, mechanics etc.) of bentonite exerting swelling pressure.