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Helsinki, Finland

Sun L.,University of Eastern Finland | Tanskanen J.T.,University of Eastern Finland | Hirvi J.T.,University of Eastern Finland | Kasa S.,Posiva Oy | And 2 more authors.
Chemical Physics | Year: 2015

Molecular dynamic simulations are employed to study the crystalline swelling behavior of montmorillonites (MMTs) with different interlayer Na+ and Ca2+ ion compositions, and the effect of temperature and pressure on the swelling behavior. Non-linear increases in d-spacing are observed with increasing water content. Plateaus in the swelling curve for Na-MMT around d-spacings of 12 and 15 Å demonstrate the formation of 1- and 2-layer hydrate structures. Ca-MMT and mixed Na/Ca-MMTs exhibit similar swelling behavior with exception of showing stronger swelling at water contents corresponding to the 1-layer hydrate in Na-MMT. The stronger swelling in the calcium containing systems is attributed to the preference of Ca2+ to be fully coordinated to water molecules, which favors a 2-layer hydrate structure and increased d-spacings. The larger hydration energy of Ca2+ ions relative to Na+ ions promotes increased water coordination numbers and more pronounced association of water molecules with Ca2+ ions. The 1- and 2-layer hydrates for Na-MMT and the 2-layer hydrate for Ca-MMT were relatively stable to changes in temperature and pressure. © 2015 Elsevier B.V. All rights reserved.


Navarro V.,University of Castilla - La Mancha | Asensio L.,University of Castilla - La Mancha | Yustres T.,University of Castilla - La Mancha | Pintado X.,BTech Oy | Alonso J.,University of Castilla - La Mancha
Engineering Geology | Year: 2014

This article proposes a new plastification mechanism to model bentonite free swelling processes by using an elastoplastic approach. The formulation is based on an interaction function that defines the plastic macrostructural strains induced by microstructural effects. This term is defined as a function of the microstructural void ratio, and it establishes a direct connection between the destructuration of the micro- and macrostructures of the bentonite during the free swelling processes. The formulation proposed also includes a new approach to the calculation of the microstructural void ratio as well as a new method to describe the kinetic mass exchange between micro- and macrostructural water, considering that there may not be equilibrium between the two types of water. The model was used to analyse several free swelling tests and was found to yield satisfactory results. © 2014 Elsevier B.V. All rights reserved.


Navarro V.,University of Castilla - La Mancha | Asensio L.,University of Castilla - La Mancha | De la Morena G.,University of Castilla - La Mancha | Pintado X.,BTech Oy | Yustres A.,University of Castilla - La Mancha
Applied Clay Science | Year: 2015

The current research proposes a method for obtaining the intra-aggregate (microstructural) and inter-aggregate (macrostructural) water content of MX-80 bentonite using data from water retention curves. Data associated with high suction were used to define the microstructural water content model. By extrapolating this model to low suction, microstructural and macrostructural water contents were separated to obtain a macrostructural water content model. Micro-and macrostructural water content models have been used to simulate an isotropic swelling test, thus illustrating the advisability of using a double and differentiated macro/micro description of the water content to characterise the hydro-mechanical behaviour of MX-80 bentonite. © 2015 Elsevier B.V.


Lavikainen L.P.,University of Eastern Finland | Hirvi J.T.,University of Eastern Finland | Kasa S.,Posiva Oy | Schatz T.,BTech Oy | Pakkanen T.A.,University of Eastern Finland
Theoretical Chemistry Accounts | Year: 2015

Phyllosilicates and related clay minerals are of interest due to a variety of technological applications and impact on natural soils. The important properties of these layered minerals arise from their surface chemistry, and therefore understanding the characteristics of their surfaces is desirable. The common focus has been on the basal surfaces, whereas the edge surfaces are little studied. One of the underlying reasons is that the edge surfaces exhibit various possible geometries making it difficult to assume a certain structure with a confidence. The present paper is dedicated to the stability of the edge structures and introduces the largest quantum chemical study on the subject to date. Pyrophyllite was used as a model species. Edge stabilities were determined as cleavage energies, including edge termination by dissociative sorption of water with variable proton configurations. The results show similar stabilities for various edge structures parallel to the (010), (130), (110) and (100) lattice planes, but the edges cleaved by cutting the fewest bonds are suggested to be the most stable on the basis of free energy estimation. The dominant edge is predicted to appear on the (110) crystal face. © 2015, Springer-Verlag Berlin Heidelberg.


Grant
Agency: Cordis | Branch: FP7 | Program: CP | Phase: Fission-2012-1.1.1 | Award Amount: 15.74M | Year: 2012

DOPAS aims to improve the adequacy and consistency regarding industrial feasibility of plugs and seals, the measurement of their characteristics, the control of their behavior over time in repository conditions and also their hydraulic performance acceptable with respect to the safety objectives. This DOPAS project addresses the design basis, reference designs and strategies to demonstrate the compliance of the reference designs to the design basis, for plugs and seals in geological disposal facilities. The project focuses on shaft seals for salt rock (German repository concept), tunnel plugs for clay rock (French and Swiss repository concepts), and tunnel plugs for crystalline rock (Czech, Finnish and Swedish repository concepts). Five different demonstration experiments are part of the project and will take place in Sweden, France, Finland, Czech Republic and Germany. They are in different state-of-development. The Swedish demonstrator will be constructed prior to start of the DOPAS project and will basically provide experience on demonstration of compliance of reference design to the design basis. German demonstrator will be installed after the DOPAS project and will focus on demonstration of suitability by performance assessment. The French, Finnish, Swedish,German and the Czech experiments will address developments in all phases of design basis, reference designs and strategies to demonstrate compliance of reference designs to design basis. The studied concepts will be developed in the DOPASs five thematic scientific/technological work packages, which each integrate the results of the individual experiments. The DOPAS project is derived from the IGD-TPs Strategic Research Agenda that points out the topic of plug and seals as a first priority issue for joint European RTD projects.

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