Coordinated project BOA

Transcription

1 VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD Coordinated project BOA 18 March 2015, KYT2014, Helsinki M. Olin 1, M. Kataja 2, L. Korkiala-Tanttu 3, P. Hölttä 4, J.-P. Suuronen 4, M. Tiljander 5, M. Laitinen 6, M. Itävaara 1, E. Myllykylä 1, A. Itälä 1, J. Järvinen 1 1 VTT Technical Research Centre of Finland Ltd, 2 University of Jyväskylä, 3 Aalto University, 4 University of Helsinki, 5 Geological Survey of Finland, 6 Numerola Oy

2 Goals THMC(B)-model, sufficiently good over whole parameter space Concept based on experimental observations Needed parameter values and data must be available somehow Mathematical formulation consistent and completed Implementation possible to carry out by present computing methods, tools and resources Characterisation and analysis methods, by which all needed determinations can be done Accurate, repeatable and reliable Process experiments, which support modelling and vice versa; supported characterisation and analysis methods Carefully selected set of experiments and tests NOT a goal: to solve all bentonite issues, but instead to create operations model to study bentonite effectively 30/04/2015 2

3 Results 3

4 Results briefly 1. Aalto: Block Shear has been investigating the shear resistance between various tunnel backfill interfaces in the KBS-3V. 2. GTK: Development of characterization of bentonite material 3. Numerola: New numerical THM-solver was implemented and validated for simulating bentonite buffer 4. Jyväskylä: A non-invasive method for measuring the threedimensional displacement field and water content distribution in a wetting and swelling bentonite using X-ray tomographic imaging is developed. 5. HYRL has developed methods for bentonite colloid measurements and has studied sorption of radionuclides onto those colloids. 6. HYFL: Studies were carried out on the nanostructure of bentonite and purified montmorillonite at the 30/04/2015 4

5 Results VTT VTT: The electrodes for measuring Na +, Ca 2+, and SO 4 2- ions have been developed and tested. VTT: The dissolution study of Ca and Na montmorillonite in groundwater simulants (2 g/l) indicated that the nature of the smectite mineral did not change over 140 days. VTT: Cation exchange - The analysing accuracy of tested methods appeared to be an issue. However, any notable temperature dependence was not observed. VTT:15 year experiments - A great diversity of microorganisms, also active microorganisms were detected 30/04/2015 5

6 1. Dissolution of Na- and Ca-montmorillonite* The dissolution rates obtained are in agreement with those presented in the literature Dissolution is dependent on the experimental conditions Water composition and temperature Elevated T and higher ph have increasing effect on reactivity and thus on the solubility XRD results indicated that the the smectite minerals did not alter Myllykylä et al Clay Minerals, vol. 48 Instead, the experimental conditions more or less modified the structure of montmorilllonite (e.g. layer stacking). 30/04/ * With ERM (Etudes Recherches Matériaux, France)

7 2. Cation exchange experiments Non-compacted experiments Usefulness of ion selective electrodes was tested and one thesis was done around the subject At the end it was found out that perchlorate background interferes with electrodes too much Na/Ca exchange on different temperatures Lots of problems with accuracy of the analyses In the end conclusion was that not much difference between different temperatures was found Na equivalent fraction in exchanger Celcius 0.1N 50 Celcius 0.1N 75 Celcius 0.1N Sposito 25 Celcius 0.05N Modelled 25 Celcius 0.1 N Modelled 50 Celcius 0.1 N Modelled 75 Celcius 0.1N Na equivalent fraction in solution *Exchange isotherm of Na + on Na-montmorillonite in perchlorate background for Na-Ca exchange. 30/04/2015 7

8 3. Microbiology ( ) Merja Itävaara, Marjaana Rättö, Pauliina Rajala, Mari Raulio (SEM), Elina Sohlberg BOA 2011 Literature survey: What is known about microorganisms in the bentonite Extremophiles; Life in extreme environments Microbes in bentonite BOA 2012 DNA extraction methods for microbes in bentonite BOA Bacteria and fungi analyzed from the long term experiment (15 year s bentonite experiment METHODS: SEM DNA and RNA extraction PCR-DGGE, Sequencing Bioinformatics 30/04/2015 8

9 Summary of microbiology results (15 year s experiment) Soil bacteria adapted to dry, thermophilic, high radiation resistant environment and forming endospores present in the copper/bentonite interface In addition bacteria able to oxidize iron, fix nitrogen and involved in sulphur metabolism present Active (rrna) bacteria communities present, however, smaller than the inactive (DNA) Wide diversity of fungi present (fungi may produce acids and penetrate by their hyphae through long distances SEM micrographs of microbes in bentonite PCR-DGGE of fungi Fungi in bentonite 30/04/2015 9

10 4. Mineralogy of bentonite Bentonite, a material consisting predominantly of smectite minerals. The focus of the research is to study 1. Acessory minerals of bentonite 2. Smectite mineralogy Methods: 1. X-ray diffraction (XRD) 2. Scanning electron microscope (SEM) 3. Electron probe micro-analyzer (EPMA) Targets Montmorillonite dissolution 15 year experiments Structural studies SEM: Concentration of the mineral phases EPMA: Quantitative analysis from mineral phases XRD: Qualitative mineral compositon 30/04/

11 5. Small-angle x-ray scattering patterns of Camontmorillonite (SAXS) According to SAXS results the well-ordered coherently scattering clay stacks include 6-8 platelets per stack. In the figure the spacings corresponding to 1-4 water layer hydration states are denoted by 1W, 2W, 3W and 4W. M. Matusewicz et al Clay Minerals. Vol /04/

12 6. Block shear experiments Large shear box tests have been done with different materials existing in Finnish KBS-3V method. The aim was to define the interface properties for modelling purpose Shear resistance increased with increasing salt concentration If the water content of materials were less than 40%, the shearing took place at the interfaces. With higher water contents the shearing took place within materials going towards the internal shear resistance of materials The increase of temperature (+20 C to +80 C) did not affect shearing resistance. 30/04/ Friction angle, Friedland block pellet Pellet internal Water content, % Friedland block granule Granule internal

13 7. Numerola: THM modeling Hydromechanical model was implemented based on a phenomenological model of Markku Kataja (JyU) and experiments of JyU Hydromechanical model was validated by simulating bentonite wetting and swelling of JyU Hydrological transport model was based on a diffusion model of two moisture phases (water vapour and liquid water) Thermal solver was based on a heat conduction model with a moisture dependent conduction coefficient. The bentonite chemistry model for five ions was updated and tested in collaboration with VTT Comparison of simulated (blue) and measured (red) deformations in a swelling experiment of bentonite. The color gradient shows measured water content. 30/04/

14 8. 4D measurement of wetting/swelling of bentonite based on X-ray microtomography X-ray tomographic scanner Sample holder with wetting channels Compacted bentonite sample Force sensor Venting channel Plastic tube (PEEK) Sintered blocks Bentonite sample Wetting channel 20 mm Results: Non-intrusive method based on X-ray tomography for measuring water transport and swelling of bentonite has been developed [1]. The method have been used to measure wetting and swelling of purified bentonite samples in constrained volume. The data is available and can be used e.g. for validation of hydromechanical models. Measured 3D deformation and water content field in (one half of) a cylindrical bentonite sample [1] Harjupatana T, Alaraudanjoki J and Kataja M, "An X-ray tomographic method for measuring three-dimensional deformations and liquid transport in swelling clays", Submitted in Applied Clay Science, (2015). 30/04/

15 7. The effect of colloids on radionuclide migration: Formation and stability of colloids Particle concentration (left) and zeta potential (right) of colloids formed from MX-80 bentonite powder in OLSO solutions. Only in dilute solutions (1 10 mm), particle diameter was under 500 nm and ZP lower than -30 mv, indicating stable colloids. Mean particle concentration (left) and zeta potential (right) of colloids formed from MX-80 bentonite pellets in Allard and OLSO solutions with gentle agitation. 30/04/2015 WM

16 The effect of colloids on radionuclide migration: Radionuclide sorption on bentonite colloids 85 Sr and 152 Eu sorption (K d ) on colloids was determined as a function of ph and ionic strength, which have a great influence on their adsorption. 237 Np (V) sorption on corundum, bentonite colloids and montmorillonite was determined using batch method and Zeta potential, in-situ ATR FT-IR and EXAFS spectroscopy to study the chemical nature of the complex between neptunium and mineral. (poster) 30/04/2015 WM

17 Safety functions

18 Rock, crushed rock and compacted bentonite Buffer material demands: low hydraulic conductivity (K), low diffusion conductivity (D e ) and high enough ductility Granitic rock: lowkand D e, but it is brittle and difficult to apply Crushed rock: high K and D e, porosity is high, easy to use Bentonite: lowd e for anions, acceptable for cations, and very low K, and is ductile How highly porous bentonite can have all these properties? Why the diffusivity values are different for anions and cations? Specific microstructure of bentonite: very small pores, interaction of ions with pore surfaces Dry density (kg/m 3 ) Porosity (-) Hydraulic cond. K (m/s) D e anions (m 2 /s) D e cations (m 2 /s) rock E E E-13 crushed rock E E E-11 bentonite E E E-11 30/04/

19 Variation of conditions for bentonite buffer in KBS3 method Thermodynamic variables Temperature, T Pressure, P Chemical composition Water, S Solid: minerals + exchanged cations, d Dissolved salts, I d : kg/m 3 Montmorillonite + exchanged cations + other accessory minerals S: Dry - fully saturated T: o C P: MPa + ice cover I: 0.01 mm 1 M 1 mg/l 100 g/l Na-Ca-Cl + other ions, microbes, colloids 30/04/

20 Scales, properties of bentonite and water phase Spatial scales Colloidal size Pore size Laboratory Small scale Pilot scale Repository scale Time scales Nanoseconds in molecular dynamics Lab = days to years Repository = years to millenia Compacted bentonite sample 20 mm Bentonite properties Relative amount of montmorillonite Cationic form of montmorillonite Accessory minerals Grain size Initial water content History of the samples Production Transport Processing Water Humidity or saturation Composition Gases Electrolyte Groundwater simulant Colloids Microbes 30/04/

21 30/04/

22 Microbes related to processes and structure Boxes of yellow colour = safety functions Canister survives in dislocations Montmorillonite losses by erosion Homogenisation Formation and transport of colloids Deformations and stresses, friction self healing Hardening Alteration Dissolution Montmorillonite: solid part Water: free Diffusion Water: bound Cations: bound Microbial activity Minerals: solid and dissolved RN transport limited to diffusion, sorption Corroding agents in and products out Cation exchange and chemistry 30/04/

23 Methods and tools Quantum mechanics NMR XRD SAXS Molecular dynamics Number and distribution of water layers TEM SEM Mesoscale structure: nm Nano tomography Mesoscale modelling Pores: free, interlamellar, diffuse layer Micro tomography THC EPMA Colloids DLVO ICP-MS analysis THC Geochemist s Workbench Basic characterisation Pore size distribution vs. density Colloids: formation and RN transport Dissolution and precipitation of montmorillonite Dissolution and precipitation of other minerals THC TOUGHREACT Microstructure of bentonite Processes of bentonite Cation exchange and diffusion Differences between Na and Ca (K, Mg too) Microbes: analysis and effects Deformations and stresses, friction Wetting and homogenisation Diffusion and sorption THMC(B) COMSOL THM Numerrin Mechanical properties 30/04/ ISE

24 Conclusions 24

25 Goals vs. results THMC(B)-model, sufficiently good over whole parameter space Concept based on experimental observations we are on this way Needed parameter values and data data production started Mathematical formulation consistent and completed better models now Implementation possible to carry out by present computing methods, tools and resources - ok Characterisation and analysis methods, by which all needed determinations can be done Accurate, repeatable and reliable many new methods developed and tested Process experiments, which support modelling and vice versa; supported characterisation and analysis methods Carefully selected set of experiments and tests started -> THEBES NOT a goal: to solve all bentonite issues, but instead to create operations model to study bentonite effectively success here too, and more will be done in THEBES 30/04/

26 Conclusions and future Still much to study about bentonite in KBS3 method New methods are promising and already producing publishable results Need of large collaboration between Geologists Physicists Chemists Computer scientists Good luck for the THEBES project in KYT /04/

27 TECHNOLOGY FOR BUSINESS