Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Characterization of rock samples from Äspö Some results from EU-CROCK Project WP1 Annual Science Meeting of the National Geosphere Laboratory Oskarshamn Stellan Holgersson

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Introduction The aim: ”to decrease conservatism in the crystalline host-rock high level waste repository far-field safety assessment” CROCK – Crystalline Rock Retention Processes The approach: “The experimental program reaches from the nano-resolution to the relevant real site scale, delineating physical and chemical retention processes. Existing and new analytical information provided within the project is used to set up step-wise methodologies for up-scaling of processes from the nano-scale through to the km- scale. Modeling includes testing up-scaling process and parameters for the application to Performance Assessment and in particular, the reduction of uncertainty.”

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Introduction Work Packages :  WP1: Organization and characterization of rock samples from Äspö  WP2: Experimental (laboratory scale) sorption/migration studies  WP3: Natural homologues and real system analyses using existing databases  WP4: Conceptualization of results from WP1-3 and modelling  WP5: Application to modelling of a safety case  + documentation, etc CROCK – Crystalline Rock Retention Processes Project leader : KIT (DE) Participants: AMPHOS (ES), CIEMAT (ES), CONTERRA (SE), CTH (SE), FZD (DE), KEMAKTA (SE), NRI (CZ), VTT (FI)

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Background Contaminant transport in the geosphere: Picture from USGS ( A general problem that (should) concern all of us

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Background Contaminant transport in the geosphere: Potential sources Landfills Former industrial sites Waste repositories Natural ores

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Contamination Transport Contaminant transport in the geosphere: conceptual model (1) Industrial sites animation courtesy: I. Dubois fractures pores

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Contamination Transport Contaminant transport in the geosphere: conceptual model (2) Industrial sites M+ Contaminant metal is adsorbed on surface oxygen sites (chemical retention) adsorption depends on surface area and the available porosity Q: the area and porosity are connected, but how?

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Objectives Preparation of samples for sorption and diffusion experiments Determination of Specific Surface Area SSA (m 2 /g) Determination of Specific Pore Volume SPV (mL/g) Determination of apparent density (kg/m 3 )

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Sampling at Äspö Drilling in NASA2376A, May to obtain drill-cores....preserved in inert atmosphere. photos courtesy: S. Buechner

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Selection of one drill core a,A,b,B,c,C,d,D,e,E,f,F,g,G,h,H,I Sample ”1.30a” taken from m depth from tunnel wall Perpendicular fractures at both ends Cut into roughly 1.5cm long sections with a diamond saw in N 2 glove-box Samples a-h for sorption, A-H for diffusion fracture surfaces

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Further preparations The 8 samples for batch sorption were crushed and sieved into four fractions: 1-0.5mm, mm, mm, mm, giving in total 32 fractions The 8 samples for diffusion were lined with epoxi resin

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Specific Surface Area (SSA) measurements Kr gas adsorption instrument, using the BET (1 model for gas adsorption isotherm All 17 intact samples (a-h, A-H,I) were measured, using 2-4 pressure points Crushed samples (a-h) was then measured, using 7-10 pressure points 1) Brunauer, S., Emmet, P.H. and Teller, E.: Adsorption of gases in multimolecular layers. J.Am. Chem. Soc. 60 (2), (1938).

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry SSA measurements: Results intact sections

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry SSA measurements: Results crushed sections

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry SSA measurements: Results non-porous smooth spherical particles Äspö rock

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Specific PoreVolume measurements N 2 gas adsorption instrument, using BJH (1 model for isotherm Crushed samples (a-h) measured, using pressure points (absorbtion+desorption) For intact samples (A-H) the 3 H 2 O diffusion was used, since no porosity can be detected with gas adsorption 1) Barrett, E.P., Joyner, L.G. and Halenda, P.P.: The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms. J.Am. Chem. Soc. 73 (1), (1951). rock disc mounted in diffusion cell

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry SPV measurements: 3 H 2 O through diffusion

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry SPV measurements: Results intact sections SPV calculated from porosity, using measured apparent densities for each section (mean 2704  21kg/m 3 )

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry SPV measurements: Results crushed sections

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry SPV measurements: Results approx. detection level w. gas adsorption gas adsorption measurements 3 H 2 O diffusion measurements ?

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Results to explain: 1)Why is it a linear slope for SSA and SPV when plotting them versus particle size? 2)Why does the large intact disc material follow this trendline in the case with SSA but not with SPV?

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry The linear dependency of SSA and SPV with particle size: The linear dependency is consistent with a model where particles contain 2-zone porosity: one outer larger porosity (”disturbed zone”) with constant thickness and one inner core of lower porosity

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Larger SPV for intact material than predicted from crushed material This phenomena can be explained with two pore types: 1)mesopores (size <0.5  m) measurable with gas adsorption in crushed material. These pores contributes to SSA and SPV. For intact material, however, the mesoporous SPV is too small to be measured with gas adsorption. 2)macropores (size >0.5  m) not measurable with gas adsorption in either crushed or intact material, because the gas do not condense in these large pores. The macroporous SPV shows up only with 3 H 2 O diffusion in intact material. It probably has a negligable SSA in comparison with the mesoporous SPV.

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Conclusions The measured SSA with gas adsorption can be described with a 2- zone porosity model: a high porosity zone surrounding a low porous core For SSA the model is consistent over the whole size range that were investigated The measured SPV with gas adsorption/condensation can also be described with the same 2-zone porosity model For SPV the model is consistent only for the smaller particles To explain the relatively large SPV in the intact disc samples, the presence of macropores (small fractures or ”fissures”) can be assumed

Chalmers University of Technology Department of Chemical and Biological Engineering – Nuclear Chemistry Acknowledgements Henrik Drake, Thorsten Schäfer, Sebastian Büchner and the MiRo drilling team are gratefully acknowledged for help with sampling of the drill cores. The research leading to these results has received funding from the European Union's European Atomic Energy Community's (Euratom) Seventh Framework Programme FP7/ under grant agreement n° (CROCK project) and SKB, the Swedish Nuclear Fuel and Waste Management Company.