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 2013-11-07

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 Processeswww.crockproject.eu

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 Processeswww.crockproject.eu

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 (www.ga.water.usgs.gov)

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

pores

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+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 (m2/g)• Determination of Specific Pore Volume SPV (mL/g)• Determination of apparent density (kg/m3)

Chalmers University of Technology

Department of Chemical and Biological Engineering – Nuclear Chemistry

Sampling at ÄspöDrilling in NASA2376A, May 2011...

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 12.1-12.4m depth from tunnel wall• Perpendicular fractures at both ends• Cut into roughly 1.5cm long sections with a diamond saw in N2 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, 0.5-0.25mm, 0.25-0.125mm, 0.125-0.063mm, 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), 309-319 (1938).

Chalmers University of Technology

Department of Chemical and Biological Engineering – Nuclear Chemistry

SSA measurements: Results intact sections Sample Core section (m)

SSA (m2/g)

a 12.385-12.4 0.0092±0.0003 A 12.37-12.385 0.0069±0.0002 b 12.355-12.37 0.0074±0.0003 B 12.34-12.355 0.0078±0.0002 c 12.325-12.34 0.0075 C 12.31-12.325 0.0061 d 12.295-12.31 0.0055±0.0002 D 12.28-12.295 0.0051 e 12.265-12.28 0.0077±0.0003 E 12.25-12.265 0.0044 f 12.235-12.25 0.0073±0.0004 F 12.22-12.235 0.0062±0.0002 g 12.205-12.22 0.0068±0.0000 G 12.19-12.175 0.0050±0.0002 h 12.175-12.19 0.0068±0.0003 H 12.16-12.175 0.0048 I 12.11-12.16 0.0080 average 0.0066±0.0013

Chalmers University of Technology

Department of Chemical and Biological Engineering – Nuclear Chemistry

SSA measurements: Results crushed sections 1-0.5mm 0.5-0.25mm 0.25-0.125mm 0.125-0.063mm

Sample Core section

(m)

SSA (m2/g)

SSA (m2/g)

SSA (m2/g)

SSA (m2/g)

a 12.385-12.4

0.1021±0.0008 0.1544±0.0010 0.2285±0.0014 0.3999±0.0015

b 12.355-12.37

0.0953±0.0008 0.1516±0.0010 0.2507±0.0011 0.3585±0.0015

c 12.325-12.34

0.0850±0.0006 0.1516±0.0008 0.2188±0.0009 0.2980±0.0017

d 12.295-12.31

0.0928±0.0005 0.1328±0.0005 0.2048±0.0006 0.3008±0.0006

e 12.265-12.28

0.0806±0.0004 0.1288±0.0005 0.1747±0.0005 0.2675±0.0008

f 12.235-12.25

0.0766±0.0003 0.1252±0.0003 0.1926±0.0004 0.2676±0.0005

g 12.205-12.22

0.0956±0.0004 0.1404±0.0004 0.1770±0.0006 0.3136±0.0009

h 12.175-12.19

0.0714±0.0009 0.1092±0.0019 0.1760±0.0023 0.2778±0.0011

average 0.0874±0.0107 0.1368±0.0158 0.2029±0.0280 0.3105±0.0468

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

• N2 gas adsorption instrument, using BJH(1 model for isotherm

• Crushed samples (a-h) measured, using 90-100 pressure points (absorbtion+desorption)

• For intact samples (A-H) the 3H2O 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), 373-380 (1951).

rock disc mounted in diffusion cell

Chalmers University of Technology

Department of Chemical and Biological Engineering – Nuclear Chemistry

SPV measurements: 3H2O 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 270421kg/m3)

Sample disc

De (m2/s)

G porosity (%) HTO

method

SPV (mL/g) HTO

method A 1.27∙10 -13 3.45∙10 -2 1.73∙10 -3 6.42∙10 -4 B 1.67∙10 -13 2.76∙10 -2 2.85∙10 -3 1.05∙10 -3 C 1.61∙10 -13 2.48∙10 -2 3.05∙10 -3 1.12∙10 -3 D 1.35∙10 -13 4.33∙10 -2 1.46∙10 -3 5.32∙10 -4 E 9.84∙10 -14 2.94∙10 -2 1.57∙10 -3 5.77∙10 -4 F 1.18∙10 -13 2.70∙10 -2 2.06∙10 -3 7.63∙10 -4 G 1.13∙10 -13 3.23∙10 -2 1.65∙10 -3 6.16∙10 -4 H 1.02∙10 -13 2.46∙10 -2 1.94∙10 -3 7.20∙10 -4 mean value 1.28±0.26

∙10-13 3.04±0.62

∙10-2 2.04±0.60

∙10-3 7.54±2.21

∙10-4

Chalmers University of Technology

Department of Chemical and Biological Engineering – Nuclear Chemistry

SPV measurements: Results crushed sections

1-0.5mm 0.5-0.25mm 0.25-0.125mm 0.125-0.063mm

Sample Core section (m)

SPV (mL/g)

SPV (mL/g)

SPV (mL/g)

SPV (mL/g)

a 12.385-12.4 3.19 10∙ -4 5.32 10∙ -4 7.28 10∙ -4 1.61 10∙ -3 b 12.355-12.37 3.42 10∙ -4 7.19 10∙ -4 9.72 10∙ -4 1.30 10∙ -3 c 12.325-12.34 5.60 10∙ -4 5.48 10∙ -4 8.22 10∙ -4 1.11 10∙ -3 d 12.295-12.31 6.12 10∙ -4 5.40∙10-4 7.74∙10-4 1.13∙10-3 e 12.265-12.28 6.99∙10-4 5.27∙10-4 7.31∙10-4 1.03∙10-3 f 12.235-12.25 5.61∙10-4 4.88∙10-4 7.94∙10-4 1.15∙10-4 g 12.205-12.22 6.40∙10-4 6.37∙10-4 7.66∙10-4 1.26∙10-3 h 12.175-12.19 6.62∙10-4 5.15∙10-4 7.25∙10-4 1.05∙10-3 average 5.49±1.43∙10-4 5.63±0.76∙10-4 7.89±0.82∙10-4 1.20±0.19∙10-3

Chalmers University of Technology

Department of Chemical and Biological Engineering – Nuclear Chemistry

SPV measurements: Results

approx. detection level w. gas adsorption

gas adsorption measurements

3H2O 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 <0.5m) 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 >0.5m) 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 3H2O 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 FP7/2007-2011 under grant agreement n° 269658 (CROCK project) and SKB, the Swedish Nuclear Fuel and Waste Management Company.