Lund, Sweden
Lund, Sweden

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Grant
Agency: European Commission | Branch: FP7 | Program: CP-FP | Phase: Fission-2009-1.1.1 | Award Amount: 6.53M | Year: 2010

The main aim of the project PEBS (Long-term Performance of the Engineered Barrier System) is to evaluate the sealing and barrier performance of the EBS with time, through development of a comprehensive approach involving experiments, model development and consideration of the potential impacts on long-term safety functions. The experiments and models cover the full range of conditions from initial emplacement of wastes (high heat generation and EBS resaturation) through to later stage establishment of near steady-state conditions, i.e. full resaturation and thermal equilibrium with the host rock. These aspects will be integrated in a manner that will lead to a more convincing connection between the initial transient state of the EBS and its long-term state that provides the required isolation of the wastes. The work proposed within the project builds on existing knowledge and experience generated during recent years and supported by ongoing nat. and EC research programmes. The project pretends to provide a more complete description of the THM and THM-C (thermo-hydromechanical-chemical) evolution of the EBS system, a more quantitative basis for relating the evolutionary behaviour to the safety functions of the system and a further clarification of the significance of residual uncertainties for long-term performance assessment. The importance of uncertainties arising from potential disagreement between the process models and the laboratory and in situ experiments to be performed within PEBS, and their implications for extrapolation of results will be reviewed, with particular emphasis on possible impacts on safety functions. In addition to the scientific-tech. aim, the consortium will spread the essential results to the european scientific community and Canada, Japan and China, use its expertise for public information purposes, and promote knowledge and technology transfer through training. WP 5 brings together activities concerning dissemination and training.


Grant
Agency: European Commission | Branch: FP7 | Program: CP-FP | Phase: Fission-2011-1.1.1 | Award Amount: 5.09M | Year: 2012

Recent safety assessments nuclear waste repositories have shown that the formation and stability of colloids may have a direct impact on the overall performance of the repository. The main aim of the BELBaR project is increase the knowledge of the processes that controls clay colloid stability, generation and ability to transport radionuclides. The overall purpose of the project will be to suggest a treatment of the issues in long-term safety assessment. The key areas of research will be: erosion of bentonite buffers, the main objective of these studies will be to understand the main mechanisms of erosion from the bentonite surface and to quantify the extent of the possible erosion under different conditions clay colloid stability studies under different geochemical conditions. The colloids formed at the near/far field interface would be stable only if favourable conditions exist and therefore their relevance for radionuclide transport will be strongly dependent on the local geochemical conditions interaction between colloids and radionuclides and the host rock, how colloid mobility may be affected be the composition of the host rock and the mechanism of sorption and de-sorption of radionuclides on the colloids In these areas substantial laboratory studies will be undertaken. The modelling studies will support the laboratory studies through development of conceptual and mathematical descriptions of the observed phenomena. The final outcome is to consider how colloids and related phenomena can be considered in the long term safety case and to make recommendations on how the safety case could pursue to address this potentially very significant issue. The project will have strong focus on cooperation and integration. This will be achieved by exchange of staff between partners and arrangement of frequent seminars. The BELBaR consortium consists of research institutes, implementers and universities from within and outside the European Union.


Dueck A.,Clay Technology AB | Borgesson L.,Clay Technology AB
Engineering Geology | Year: 2015

Results from the field experiment in the LOT project showed that compacted bentonite specimens exposed to warm field conditions had a significantly reduced strain at failure compared to the reference material. The objective of the study presented in this article was to investigate the impact of variables like temperature, density, water content and degree of saturation on the occurrence of brittleness at failure of compacted bentonite specimens. To do so, unconfined compression tests were performed on bentonite specimens exposed to different conditions in the laboratory. Brittle failure mainly took place in specimens having a dry density of ρd ≥1.69Mg/m3 or in specimens exposed to high temperature (T≥150°C). Brittle failure behaviour also took place in unsaturated specimens with a degree of saturation less than 90%. The brittle behaviour that was observed in the material exposed to high temperatures under field conditions in the LOT project was also observed in the present short term laboratory tests. However, the laboratory prepared specimens in the present study had either a higher density or lower degree of saturation or were exposed to higher temperatures than the specimens with brittle behaviour in LOT that were exposed to field conditions for several years. © 2015 Elsevier B.V.


Lonnqvist M.,Clay Technology AB | Lonnqvist M.,Chalmers University of Technology | Hokmark H.,Clay Technology AB
Journal of Geophysical Research: Earth Surface | Year: 2013

Hydraulic jacking is a significant dilation of a fracture that occurs when the pore pressure within it exceeds the sum of the fracture's normal stress and tensile strength. This phenomenon may occur during a glacial period because of changes in hydraulic and mechanical boundary conditions. Since hydraulic jacking may alter flow patterns and the transport capacity of the rock mass, its possible effects on the long-term performance of a nuclear waste repository should be considered. We develop an approach to assess glacially induced hydraulic jacking in fractured crystalline rock and establish bounding estimates of the maximum jacking depth for the Swedish Nuclear Fuel and Waste Management Company's (SKB) repository site at Forsmark. The pore pressure is estimated using mechanically uncoupled two-dimensional poroelastic continuum models with hydraulic and mechanical conditions based on SKB's reconstruction of the Weichselian glaciation at this site (120-0 ka B.P.). For warm-based conditions, the water pressure at the ice/bed interface is set at 98% of the mechanical load, whereas for glacial conditions with extensive proglacial permafrost, the corresponding water pressure is set at a (lower) annual average value. We demonstrate that the pore pressure within the uppermost kilometer of rock is mainly governed by the water pressure at the ice/bed interface and that the mechanical impact of the ice load on the pore pressure is sufficiently small to be ignored. Given the current and estimated future stress conditions at Forsmark, hydraulic jacking is mainly of concern for subhorizontal fractures, i.e., it is sufficient to consider situations when the pore pressure exceeds the vertical stress. We conclude that hydraulic jacking at Forsmark will be confined to the uppermost 200 m of the rock mass. ©2013. American Geophysical Union. All Rights Reserved.


Hsiao Y.-W.,Y. W. Hsiao | Hedstrom M.,Clay Technology AB
Journal of Physical Chemistry C | Year: 2015

We investigated NaCl diffusion between external bulk solution and bihydrated montmorillonite interlayers using atomistic molecular dynamics (MD) simulations. Two different bulk concentrations, 0.55 and 1.67 M, were tested. In both cases, the simulations showed that excess salt entered the interlayers. Barriers for Cl- entering the interlayer were calculated from the potential of mean force using adaptive biasing forces, and full consistency with the MD results was found. In part the barrier stems from hydration free energy cost for the ions moving from bulk water to clay interlayers. This cost was calculated using free-energy perturbation. We compared the equilibrium interlayer anion concentrations to ion-equilibrium thermodynamics, the general Donnan theory that includes excess free energy contributions in addition to the electrostatic Donnan potential. Numerically consistent predictions of the interlayer Cl- concentration were obtained between MD and Donnan equation when the hydration energy cost was incorporated as the excess free energy. This demonstrates the validity of using the approximation of a Donnan potential for the interlayer electrostatics. The MD density profiles show that cations and anions in the clay interlayers share the same physical space in the center of the two water layers. © 2015 American Chemical Society.


Olsson S.,Clay Technology AB | Karnland O.,Clay Technology AB
Physics and Chemistry of the Earth | Year: 2011

The Long Term Test of Buffer Material (LOT) project at the Äspö Hard Rock Laboratory, Sweden, is a series of medium-scale field experiments focused on validating models and hypotheses concerning long term processes in the bentonite buffer of a repository for high-level radioactive waste. The test parcels emplaced in crystalline bedrock consist of blocks of compacted MX80 bentonite embedding a Cu-tube equipped with a heater to simulate the heat generation from radionuclide decay. The A2 test parcel had been subjected to elevated temperature (up to 130 °C) and hydration by a Na-Ca-Cl type groundwater for almost 6. years when it was retrieved to be analysed. The analyses included determinations of chemical composition, cation exchange capacity (CEC), exchangeable cations and mineralogy. Both the bulk bentonite and dialysed, homo-ionic Na-clay (<2 μm and <0.2 μm fractions) were analysed when relevant. Sulphate was redistributed in the heated part of the buffer under the thermal and hydration gradients that prevailed during the test period. Anhydrite accumulated in the warmer parts, whereas gypsum was dissolved in the peripheral parts of the buffer where water was supplied. Carbonate dissolution increased with temperature in the warmest parts, whereas chloride behaved conservatively in all blocks. Cu was incorporated in the bentonite matrix at the surface of the Cu-tube indicating some corrosion, which may be explained by reactions in an early stage of the test when trapped oxygen existed in the system. Along with the dissolution/precipitation reactions the porewater composition changed, which resulted in replacement of exchangeable sodium by calcium and magnesium in the warmest zone. Also Mg in the clay (<2 μm and <0.2 μm fractions) displays a clear gradient with peak values at the heater. Because several of the alternative sinks for Mg were eliminated in the sample preparation prior to the chemical analysis (purified clay fractions, removal of carbonates, Na-saturation) the smectite is suggested a candidate sink for Mg. Parallel with the increase in Mg, a loss in Si is indicated and CEC tends to increase in the clay that had been heated at 130 °C. A loss in tetrahedral Si that is balanced by Al, and replacement of Al by Mg in the octahedral sheet would imply that the layer charge of the smectite increased, which would be consistent with the higher CEC values of these samples. The changes in CEC are, however, close to the analytical resolution of the CEC method and no effect of the changes in chemical composition can be detected in the XRD-characteristics of the clay. Therefore, supplementary high-resolution analyses are required to verify whether the structure of montmorillonite has altered in the test period. © 2011 Elsevier Ltd.


Wersin P.,University of Bern | Birgersson M.,Clay Technology AB
Geological Society Special Publication | Year: 2014

The interaction of steel with bentonite used as buffer material in high-level waste repositories may result in changes to the properties of the buffer. One of the repository designs (KBS-3H) developed by Posiva and SKB foresees the horizontal emplacement of so-called supercontainers, consisting of copper canisters surrounded by compacted bentonite and an outer perforated steel shell. The corrosion of the steel shell and the interaction of iron with the clay may impair the long-term safety functions of the buffer. The corrosion and iron-clay interaction processes within the KBS-3H concept were assessed with a kinetically based reactive transport model and a comprehensive thermodynamic database. The large uncertainty related to precipitation rates of corrosion products and iron silicates was considered by defining a series of test cases. The results generally indicate a limited effect on the stability of montmorillonite, thus affecting only a few centimetres next to the iron source. Upon complete corrosion only insignificant changes are predicted. These results are explained by (i) the diffusional constraint of mass transfer, (ii) low solubility of corrosion products and (iii) slow transformation kinetics of montmorillonite. Model results further suggest that the largest impact arises from 'indirect' processes, such as microbial sulphate reduction, which may lead to a strong increase in pH. © The Geological Society of London 2014.


Hokmark H.,Clay Technology AB | Lonnqvist M.,Clay Technology AB
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics | Year: 2012

The Swedish Nuclear Fuel and Waste Management Co. (SKB) are planning to construct a deep repository for permanent storage of spent nuclear fuel at about 450mdepth in crystalline rock in the Forsmark area, about 120 km north of Stockholm. The nuclear fuel will be contained in canisters consisting of a cast iron insert surrounded by a copper shell. The canisters will be emplaced in vertical deposition holes excavated in the floor of horizontal deposition tunnels and surrounded by a barrier of bentonite clay for isolation and mechanical protection. Given the near-field design established for the SKB repository, i.e. the shape and dimensions of repository openings, the response of the near-field rock to excavation and to the thermo-mechanical load, associated with the heat generated by the decaying fuel, will depend on the thermal and thermo-mechanical properties of the rock, the in situ stresses, the heat power characteristics of the deposited fuel and the repository layout, i.e. the geometrical arrangement of deposition tunnels and deposition holes. This paper gives a brief summary of the modeling conducted to establish thermal layout rules and to assess the thermal and thermo-mechanical evolution of the repository host rock on different scales. © 2012 Taylor & Francis Group, London.


Lonnqvist M.,Clay Technology AB | Hokmark H.,Clay Technology AB
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics | Year: 2012

During a glacial cycle, high pore pressures are likely to develop in the rock beneath an ice sheet or beneath a layer of permafrost in front of the ice sheet. Under certain circumstances, the pore pressure may exceed the sum of the fracture's normal stress and tensile strength resulting in a significant increase in the fracture's transmissivity - a phenomenon known as hydraulic jacking. This may have an impact on hydraulic conditions and flow patterns in a way that is difficult to assess. We investigate the potential and requirements for hydraulic jacking to be initiated at different depths during a glaciation and demonstrate the influence of hydro-mechanical couplings. The results show that the maximum jacking depth during the retreat phase is likely to be less than 100 m. If there is extensive continuous permafrost in front of the advancing ice sheet, the maximum jacking depth may be increased to 200 m. © 2012 Taylor & Francis Group, London.


Hedstrom M.,Clay Technology AB | Karnland O.,Clay Technology AB
Geochimica et Cosmochimica Acta | Year: 2012

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. © 2011 Elsevier Ltd.

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