Arto Muurinen

VTT Technical Research Centre of Finland, Esbo, Uusimaa, Finland

Are you Arto Muurinen?

Claim your profile

Publications (49)19.42 Total impact

  • Source
    A. Itälä · J. Järvinen · A. Muurinen
    [Show abstract] [Hide abstract]
    ABSTRACT: Disposal of Finnish spent nuclear fuel is planned to be based on the KBS-3 repository concept. The role of the bentonite buffer in this concept is essential, and thus the behaviour of the bentonite has to be known. The experiments in this paper concentrated on providing information about the effects of carbon dioxide CO2(g) partial pressure on compacted sodium bentonite, giving an insight into the buffering capacity. The experimental setup consisted of a hermetic box which had a CO2-adjusted atmosphere, and the bentonite was in contact with this atmosphere through water reservoirs. The results indicated that it is possible to measure online the changing pH in the porewater inside compacted bentonite using IrOx electrodes. It was found that the pH fell if the CO2 partial pressure increased above atmospheric conditions. The experimental results indicated a greater fall in pH than in our model in the test cases where CO2 was present. The pH in the experiment with 0 PCO2 remained nearly constant throughout the 5 month period. On the other hand, the pH dropped to near 6 with 0.3 PCO2 and to 5.5 with 1 PCO2.
    Full-text · Article · May 2013 · Clay Minerals
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Bentonite clay is planned to form a part of deep-geological repositories of spent nuclear fuel in several countries. The extremely long operation time of the repository requires an indepth understanding of the structure and properties of used materials. In this work the microstructure of a simplified system of Ca-montmorillonite is investigated using a set of complementary methods: X-ray diffraction, small angle X-ray scattering, nuclear magnetic resonance, transmission electron microscopy and ion exclusion. The paper presents experimental results obtained from compacted, water saturated samples in the dry density range 0.6–5 g/cm3. It can be observed that different methods yield similar quantification of water present in the interlamellar space. Combined results support the multiple porosity concept of the bentonite structure.
    Full-text · Article · May 2013 · Clay Minerals
  • Source
    A. Muurinen · T. Carlsson · A. Root
    [Show abstract] [Hide abstract]
    ABSTRACT: Water-saturated bentonite is planned to be used in many countries as an important barrier component in high-level nuclear waste (HLW) repositories. Knowledge about the microstructure of the bentonite and the distribution of water between interlayer (IL) and non-interlayer (non-IL) pores is important for modelling of long-term processes. In this work the microstructure of water-saturated samples prepared from MX-80 bentonite was studied with nuclear magnetic resonance (NMR) and small-angle X-ray scattering spectroscopy (SAXS) coupled with chloride exclusion modelling. The sample dry densities ranged between 0.7 and 1.6 g/cm3. The NMR technique was used to get information about the relative amounts of different water types. Water in smaller volume domains has a shorter relaxation time than that in larger domains due to the average closer proximity of the water to the paramagnetic Fe at the layer surfaces. The results were obtained using 1H NMR T 1ρ relaxation time measurements with the short inter-pulse CPMG method. The interpretation of the NMR results was made by fitting a sum of discrete exponentials to the observed decay curves. The SAXS measurement on bentonite samples was used to get information about the size distribution of the IL distance of montmorillonite. The chloride porosity measurements and Donnan exclusion calculations were used together with the SAXS results to evaluate the bentonite microstructure. In the model, the montmorillonite layers were organized in stacks having IL water between the layers and non-IL water between the stacks. In the modelling, the number of layers in the stacks was used as fitting parameters which determined the IL and non-IL surface areas. The fitting parameters were adjusted so that the modelled chloride concentration was equal to the measured one. The NMR studies and SAXS studies coupled with the Cl porosity measurements provided very similar pictures of how the porewater is divided in two phases in bentonite.
    Preview · Article · May 2013 · Clay Minerals
  • Torbjörn Carlsson · Arto Muurinen · Andrew Root
    [Show abstract] [Hide abstract]
    ABSTRACT: Bentonite is planned to be used in many countries as an important barrier in high-level waste repositories. Assessment of the barrier with regard to, inter alia, its ability to hinder transport of dissolved radionuclides leaking from a damaged canister containing spent nuclear fuel, requires quantitative data about the pore structure inside bentonite. The present NMR study was made in order to determine the number of distinguishable porewater phases in compacted water-saturated samples of MX-80 bentonite and Na-montmorillonite. The samples were compacted to dry densities in the interval 0.7-1.6 g/cm3 and subsequently saturated with Milli-Q water or 0.1 M NaCl solution in equilibrium cells. The NMR measurements were performed with a high-field 270 MHz NMR spectrometer using a short inter-pulse CPMG method to study proton T1ρ relaxation. The measured relaxation curves were found to consist of one faster and one slower proton relaxation. Subsequent analysis of the data indicated that the faster relaxation was associated with interlayer (IL) water between montmorillonite unit layers, while the slower one was associated with non-interlayer (non-IL) water located outside the interlayer spaces. The results indicate for compacted samples with a dry density of ≥ 1.0 g/cm3, that Na montmorillonite contains a larger relative volume of non-IL water than the corresponding MX-80 bentonite. This in turn, suggests that the stacking number in Na-montmorillonite is smaller than in MX-80 bentonite. Changing the porewater chemistry seemed to have some effect on the non-IL water content in the Na montmorillonite but not in the MX-80 bentonite.
    No preview · Article · Jan 2013 · MRS Online Proceeding Library
  • [Show abstract] [Hide abstract]
    ABSTRACT: Scientific Basis for Nuclear Waste Management, MRS Symposium Proceedings. Graym Walter, Triay, Ines (eds). Vol. 465, 1011 - 1018
    No preview · Article · Jan 2012 · MRS Online Proceeding Library
  • Aku Itälä · Arto Muurinen
    [Show abstract] [Hide abstract]
    ABSTRACT: The Finnish spent nuclear fuel disposal is based on the Swedish KBS-3 concept in crystalline bedrock. The concept aims at long-term isolation and containment of spent fuel in copper canisters surrounded by bentonite buffer which mostly consists of montmorillonite. For the long-term modelling of the chemical processes in the buffer, the cation-exchange selectivity coefficients have to be known at different temperatures. In this work, the cation-exchange selectivity coefficients and cation-exchange isotherms were determined in batch experiments for montmorillonite at three different temperatures (25 °C, 50 °C and 75 °C). Five different ratios of NaClO4/Ca(ClO4)2 were used in the experimental solutions. After equilibration the solution and montmorillonite were separated and the solution analysed to get the desired exchange parameters. The experiments were modelled with a computational model capable of taking into account the physicochemical processes that take place in the experiment.
    No preview · Article · Jan 2012 · MRS Online Proceeding Library
  • T. Carlsson · A. Muurinen · M. Matusevvicz · A. Root
    [Show abstract] [Hide abstract]
    ABSTRACT: Bentonite is planned to be used in many countries as a buffer material in repositories for spent nuclear fuel. The proper understanding and modelling of the functioning of the water-saturated bentonite requires knowledge about the bentonite microstructure and also the way water is distributed between different phases. This paper presents experimental results from our studies of water in compacted, water-saturated MX-80 bentonite at dry densities in the range 0.7-1.6 g/cm3. Three techniques, Cl-porosity, SAXS and proton NMR measurements, were applied to samples kept at room temperature, while TEM imaging was applied to high pressure frozen samples. The combined results of these techniques strongly indicate that the two major water phases in the compacted MX-80 bentonite samples are 'interlayer' and 'non-interlayer' water. The results of the relative amounts of different water types by SAXS and NMR are very similar. The results by Cl-porosity measurement indicate that only part of the non-interlayer water is available for anions. Those observations are discussed in comparison to TEM micrographs. Our study provides solid experimental evidence for the presence of two major water phases in water-saturated bentonite and estimates their relative proportions and pore sizes.
    No preview · Article · Jan 2012
  • Veli-Matti S. Pulkkanen · Aku P. Itälä · Arto K. Muurinen
    [Show abstract] [Hide abstract]
    ABSTRACT: A bentonite buffer is a part of the engineering barrier system of the geological disposal concept for spent nuclear fuel in Finland. The chemical conditions in the bentonite porewater determine the solubility, speciation and diffusion/sorption behaviour of the radionuclides in the bentonite. The OH-groups on the edge sites of the montmorillonite, the main component of bentonite, can buffer the pH conditions especially in the case that the buffering capacity of the accessory minerals is small. In this work, the pH conditions created by the interaction of sodium montmorillonite and an acetate buffer solution were studied experimentally in batch experiments and in compacted sodium montmorillonite. In the experiment with the compacted sample, the ends of an 18.4 mm long cylinder were exposed to an external solution of 0.3 M NaCl and 0.1 M acetate adjusted to pH 5 with NaOH. The effects were monitored by measuring the pH in the montmorillonite sample at 5 mm and 9.2 mm from the solution-montmorillonite interface as a function of time. The batch experiment was modelled considering the surface reactions of montmorillonite and the dissolution reactions of calcite and the added constituents to explain the observed phenomena.
    No preview · Article · Jan 2012 · MRS Online Proceeding Library
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the report main results form a KYT2010 programme's project Coupled behaviour of bentonite buffer (PUSKURI) are presented. In THC modelling, Aku Itälä made and published his Master of Science Thesis. Itälä was able to successfully model the LOT-experiment. Additionally, he also listed problems and development proposals for THC-modelling of bentonite buffer. VTT and Numerola created in collaboration a model coupling saturation, diffusion and cation exchange; the model was implemented and tested in Numerrin, COMSOL and TOUGHREACT. Petri Jussila's PhD THM-model was implemented into COMSOL to facilitate further development. At GTK, the mineralogical characterisation of bentonite was planned. The previous THM model (Jussila's model) including only small deformations was successfully generalized to finite deformations in way at least formally preserving the original formalism. It appears that the theory allows also a possibility to include finite plastic deformations in the theory. In order to measure the relevant mechanical properties of compacted bentonite, two different experiments, namely hydrostatic compression experiment and one-dimensional compression experiment were designed. In the hydrostatic compression experiment, a cylindrical sample of compacted bentonite covered with liquid rubber coating is placed in the sample chamber equipped with a piston. The same device was also used in one-dimensional compression experiment. X-ray microtomographic techniques were used in order to study the basic mechanisms of water transport in bentonite. The preliminary results indicate that in the present experimental set-up, water transport is dominated by a dispersive mechanism such as diffusion of vapour in gas phase or diffusion of water in solid phase.
    No preview · Article · Jan 2011 · VTT Tiedotteita - Valtion Teknillinen Tutkimuskeskus
  • Heikki Kumpulainen · A. Muurinen · K. Uusheimo
    [Show abstract] [Hide abstract]
    ABSTRACT: The microfracturing of rock matrix around fractures was studied experimentally by determining the diffusion properties of a non-sorbing tracer. The diffusivities were measured by tracer techniques using 36C1 isotope as a tracer and 0.0044 M or 1 M NaCl solutions. The diffusivities were also determined by measuring the electrical resistivities of the samples saturated with 1 M NaCl solution. The rock samples were granite around a partially filled carbonate fracture and gneiss around a slickenside fracture.The apparent diffusivities of all the studied samples were approximately of the same order of magnitude. None of the variables, i.e. salt concentration of the solution, rock and fracture type or distance from the fracture surface, had any significant effect on the apparent diffusivities.The effective diffusivities and porosities, on the other hand, depended strongly on the salt concentration of tha water used to saturate the rock samples. Possible reasons for this could be the alteration of the pore structure or change of the electrical double layer during the saturation of the rock with strong NaCl solution.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library

  • No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • Arto Muurinen · Jarmo Lehikoinen
    [Show abstract] [Hide abstract]
    ABSTRACT: The evolution of porewater chemistry in bentonite was studied in solution-bentonite interaction experiments under anaerobic conditions at room temperature. The parameters varied were the bentonite density, bentonite-to-water ratio (b/w), ionic strength of the solution, and the composition of bentonite. At the end of the experiment, the equilibrating solution and the porewater squeezed out of the bentonite samples were analyzed. This paper presents the preliminary experimental results of these ongoing studies. The evolution of porewater chemistry was determined by the dissolving components initially present in the bentonite together with the ions coming with water from the surroundings. Ion-exchange processes occurred between the exchangeable cations of montmorillonite and the cations in the water. The obtained concentrations in the external solution and porewater strongly depended on the b/w used. The concentrations in the squeezed porewaters were clearly lower than in the external waters and decreased with increasing density during squeezing.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the present study, well-characterized mesoporous silica was used as a reference material for crystalline rock. Saturation-leaching and through-diffusion tracer experiments were systematically carried out to determine the adsorption capacity factors and apparent and effective diffusivities for the radioactive tracers 3H, 22Na and 36Cl. The ionic strength of the supporting NaCl electrolyte, in equilibrium with atmospheric air, was either 0.002 M or 0.1 M. The apparent diffusivities derived from saturation-leaching experiments reveal that equilibrium adsorption on a negatively charged silica surface does not act to retard the mass transfer of sodium ions. The steady-state diffusion results are found to demonstrate the increasing break-through for sodium with decreasing ionic strength of the background electrolyte in comparison to 3H. These observations are consistent with the picture of chloride ion exclusion and of the diffuse double layer surface-excess for sodium ions being transported in the direction of the macroscopic concentration gradient. Furthermore, they are shown to be at odds with the widely adopted macroscopic pore diffusion model, which neglects the mobility of the counter-ion surface- excess.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • M. Olin · J. Lehikoinen · A. Muurinen

    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • J. Lehikoinen · A. Muurinen · M. Olin

    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • Torbjoern Carlsson · Arto Muurinen
    [Show abstract] [Hide abstract]
    ABSTRACT: The low-content free water and high swelling pressure in compacted bentonite, planned to be used as a buffer in nuclear waste repositories, create adverse conditions for direct measurements of the chemical conditions. This paper presents laboratory results from online measurements with Eh and pH electrodes in water-saturated compacted MX-80 bentonite. The Eh was measured with Au and Pt wires as electrodes, while the pH was determined with IrOx electrodes. The latter were prepared in accordance with the method by Yao et al. [1]. The measurements were carried out in two types of cells: 'squeezing cells' and 'diffusion cells'. The squeezing cell excludes almost completely all chemical interactions between the sample and the surrounding environment outside the cell. The diffusion cell, on the other hand, contains a sample that stays in contact with an external solution and therefore allows following of the physico-chemical interaction between the sample and the external solution. The measuring electrodes were positioned inside the cell in the compacted bentonite, while the reference electrode was positioned outside the cell. (authors)
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • Heikki Kumpulainen · Jarmo Lehikoinen · Arto Muurinen
    [Show abstract] [Hide abstract]
    ABSTRACT: The near-field chemistry of the repository for spent nuclear fuel arising from interactions between the groundwater, compacted bentonite clay, canister and the spent fuel was calculated using a three-successive-closed-systems approach. The calculations were performed for fresh granitic and saline groundwaters using the thermodynamic computer codes, HYDRAQL/CE and EQ3/6. The effects of water chemistry inside the canister as well as water radiolysis on fuel dissolution were taken into consideration. The groundwater and the three barriers of the nearfield were accounted for by this approach, with particular emphasis given to the pH, Eh and actinide solubilities.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • Arto Muurinen · Kaija Ollila · Jarmo Lehikoinen
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study the diffusion of uranium dissolved from uranium oxide fuel was studied experimentally in compacted sodium bentonite (Wyoming bentonite MX-80). The parameters varied in the study were the density of bentonite, the salt content of the solution and the redox conditions. In the studies with non-saline water of total dissolved solids about 300 ppm, uranium was both in aerobic and anaerobic experiments as anionic complexes and followed the anionic diffusion mechanism. Anion exclusion decreased effective diffusion coefficients, especially in more dense samples. In the studies with saline water of total dissolves solids about 35000 ppm, uranium appeared in the aerobic experiments probably as cationic complexes and followed the cationic diffusion mechanism. Uranium in the saline, anaerobic experiment was probably U(OH)4 and followed the diffusion mechanism of neutral species.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • Arto Muurinen · Torbjörn Carlsson
    [Show abstract] [Hide abstract]
    ABSTRACT: The low content of free water and high swelling pressure in compacted bentonite, planned to be used as a buffer in nuclear waste repositories, create adverse conditions for direct measurements of the chemical conditions. This paper presents results from on-line measurements with Eh and pH electrodes in water-saturated compacted MX-80 bentonite. The Eh was measured with Au- and Pt-wires as electrodes, while the pH was determined with IrOx electrodes. The measurements have been carried out in closed bentonite cells and in cells where the bentonite is in contact with an outside solution through a filter plate, so that the experimental conditions can be changed during the experiment. The results suggest that it is possible to measure pH and Eh in compacted bentonite, which improves the possibilities of obtaining information about the chemical processes occurring in the bentonite.
    No preview · Article · Jan 2010 · Applied Clay Science
  • [Show abstract] [Hide abstract]
    ABSTRACT: The KBS-3 underground nuclear waste repository concept designed by the Swedish Nuclear Fuel and Waste Management Co. (SKB) includes a bentonite buffer barrier surrounding the copper canisters and the iron insert where spent nuclear fuel will be placed. Bentonite is also part of the backfill material used to seal the access and deposition tunnels of the repository. The bentonite barrier has three main safety functions: to ensure the physical stability of the canister, to retard the intrusion of groundwater to the canisters, and in case of canister failure, to retard the migration of radionuclides to the geosphere. Laboratory experiments (< 10 years long) have provided evidence of the control exerted by accessory minerals and clay surfaces on the pore water chemistry. The evolution of the pore water chemistry will be a primordial factor on the long-term stability of the bentonite barrier, which is a key issue in the safety assessments of the KBS-3 concept.
    No preview · Article · Oct 2008 · Journal of Contaminant Hydrology