The behaviour of bentonite based materials: insight into nano and - PowerPoint PPT Presentation

THEBES: KYT project investigating bentonite 1 st THEBES workshop, Aalto University 11 th December 2015 The behaviour of bentonite based materials: insight into nano and micro-structure Pierre Delage Ecole Nationale des Ponts et Chaussées, Paris Laboratoire Navier/CERMES

Outline of the presentation • Bentonite materials in nuclear waste disposals • Microstructure issues in compacted bentonites and sand bentonite mixtures: • Hydration of compacted bentonites • Nanostructure issues during hydration • Consequences on water retention • Consequences on water transfer • Consequences on technological voids • Conclusions 2

Outline of the presentation • Bentonite materials in nuclear waste disposals • Microstructure issues in compacted bentonites and sand bentonite mixtures: • Hydration of compacted bentonites • Nanostructure issues during hydration • Consequences on water retention • Consequences on water transfer • Consequences on technological voids • Conclusions 3

Role of the disposal • To impede water circulation – Canister – Engineered barrier – Geological barrier – Structure of the disposal • To immobilise radionuclides into the canisters • To delay and attenuate the migration of radionuclides (> 500 000 y.) Multibarrier concept including engineered barrier and host rock 4 ANDRA 2005

Multi-barrier system (vertical deposit) 5 SKB

SKB concept 6 SKB, Posiva

Swiss concept High Level Waste Intermediate Level Waste Opalinus clay Compacted bentonite 7

Deep geological disposal: French concept Saturation ANDRA 2005 (EDZ)

COx Claystone Ø Stable geological context (155 Ma) Ø Very low permeability: 10 -20 10 -21 m 2 Ø Good ability for radionuclides retention Ø Porosity : 14 – 19% Ø Clay fraction: 48-50% at 490 m Photo ANDRA

Blocks of compacted bentonite Closed after 9 years hydration Technological voids 10 FEBEX project (1996), Grimsel URL FEBEX project (2005)

Pellets 11 Posiva

NAGRA Concept Bentonite pellets Bentonite blocks 12 Nagra

HE-E experiment (Nagra) 13

Outline of the presentation • Bentonite materials in nuclear waste disposals • Microstructure issues in compacted bentonites and sand bentonite mixtures: 14

Some typical characteristics of bentonites Clay FoCa7 clay (F) Kunigel (J) MX 80 (US) Mineralogy Kaolinite- smectite 64% Na smectite 85% Na - Ca smectite w L (%) 112 474 520 w P (%) 50 27 62 I P 62 447 458 ρ s 2.67 Mg/m 3 2.79 Mg/m 3 2.65 Mg/m 3 Activity 0.78 6.9 5.4 Specific surface 300 m 2 /g 687 m 2 /g 700 m 2 /g Cation Exchange 54 mEq/100 g 73,2 mEq/100 g 68 mEq/100 g Capacity 15 Tessier et al. (1998), Komine & Ogata (1992), Pusch (1992)

SEM Photo, Compacted Kunigel clay 5 µ m Inter-aggregates DRY pores Clay aggregates ρ = 2 Mg/m 3 w = 8% s = 57 MPa 2 µ m 16 Cui et al. (2002) Cui, Loiseau and Delage 2002

Sand (35%) - MX80 (65%) mixture 100 Percentage passing (%) 80 Deflocculated bentonite Sand 60 Bentonite grains Sand grains 40 Bentonite grains 20 Deflocculated bentonite (hydrometer) 0 0.0001 0.001 0.01 0.1 1 10 17 Grain size (mm) Saba, Delage et al. Eng. Geol 2014

Mercury intrusion pore size distribution Laplace’s law : increasing Hg pressure 1 1 ⎛ ⎞ p cos ⎜ ⎟ = θ + ⎜ ⎟ r r ⎝ ⎠ 200 MPa 1 2 0.00 0.4 Cylindrical pore : r 1 = r 2 0.01 0.1 1 10 100 ⎛ 1 ⎞ p 2 cos ⎜ ⎟ = θ 0.3 ⎜ ⎟ r ⎝ ⎠ Hg penetrating 1 Porosity 0.2 Higher Hg (non wetting) 0.1 pressure penetrates b smaller pores 0.0 0.01 0.1 1 10 100 Entrance pore diameter (µm) 3.5 nm in smaller and smaller pores

Mercury intrusion pore size distribution 0.15 Sand-bentonite compacted powder 0.10 dV/d(logD) ρ d = 1.8 Mg/m 3 , w = 10%, S r = 55%, s = 75.5 MPa 0.05 a 0.00 0.4 0.01 0.1 1 10 100 Not intruded < 3.5 nm 0.3 s = 75.5 MPa Porosity 0.2 0.1 b 0.0 19 0.01 0.1 1 10 100 Saba, Delage et al. Eng. Geol 2014 Entrance pore diameter (µm)

2- Microstructure at initial state Pore size distribution curve Platelet Grain Sand-bentonite compacted powder Macropores ρ d = 1.8 Mg/m 3 , w = 10%, S r = 55%, s = 75.5 MPa Micropores 0.14 0.12 0.1 dV/d(logD) 0.08 0.06 0.04 0.02 0 0.001 0.01 0.1 1 10 100 1000 0.019 µ m 22 µ m Entrance pore diameter D (µm) Micropores: intra-granular Macropores: inter-grains Simona SABA - PhD 20 /48 Defense – 9 Dec 2013 Saba, Delage et al. Eng. Geol 2014

Microfocus X-Ray Computed Tomography ( µ CT) Imager/Detector X-Ray Source Sample Rotation disk Translation rails 21 http://navier.enpc.fr Saba, Delage et al. Eng. Geol 2014

2- Microstructure at initial state Sand-bentonite compacted powder 30 µ m voxel size 65% MX80 bentonite, 35% sand, ρ d = 1.8 Mg/m 3 , s = 76 MPa, S r = 55% 50 mm 4 mm 10 mm Simona SABA - PhD 22 /48 Defense – 9 Dec 2013 Saba, Delage et al. Eng. Geol 2014

2- Microstructure at initial state Horizontal µ CT cross section Aggregation of bentonite grains Sand Well defined bentonite grains 50 mm Pore Bentonite Simona SABA - PhD 23 /48 Defense – 9 Dec 2013 Saba, Delage et al. Eng. Geol 2014

2- Microstructure at initial state Image analysis (ImageJ) 3D Median filter (2x2x2 vox) ▌ Segmentation Linear Linear Logarithmic Logarithmic 73 73 Image histogram Segmented Threshold image 73 « Mixture Modelling» function Simona SABA - PhD 24 /48 Defense – 9 Dec 2013 Saba, Delage et al. Eng. Geol 2014

2- Microstructure at initial state Heterogeneity in porosity 0.07 5 0.06 0.05 Porosity (> 30 µ m) Pores > 30 µ m (voxel size) 0.04 0.03 4 3 0.02 2 1 0.01 Mean value = 0.016 0.00 0.3 0 5 10 15 20 25 30 0.25 Distance fron centre (mm) Cumulative porosity 0.2 0.15 0.1 0.05 0.026 0 Simona SABA - PhD 25 /48 0.001 0.01 0.1 1 10 100 1000 Defense – 9 Dec 2013 30 µ m Entrance pore diameter D (µm) Saba, Delage et al. Eng. Geol 2014

Outline of the presentation • Bentonite materials in nuclear waste disposals • Microstructure issues in compacted bentonites and sand bentonite mixtures: • Hydration of compacted bentonites 26

Sand-bentonite mixture PSD 0.15 0.10 dV/d(logD) 0.05 a 0.00 0.4 0.01 0.1 1 10 100 Not intruded < 3.5 nm 0.3 s = 75.5 MPa Porosity 0.2 0.1 b 0.0 27 0.01 0.1 1 10 100 Entrance pore diameter (µm)

Effect of water content 1.1 e = 1.008 1.0 w = 12.5%, s = 30 MPa 0.9 Intruded mercury void ratio, e m 0.812 0.8 MX 80 clay w = 28.5% ρ = 2 Mg/m 3 0.7 w = 12.5 % s = 2 MPa 0.597 0.6 0.5 0.4 w = 28.5 % 0.293 0.3 0.2 0.230 0.1 0.0 0.001 0.01 0.1 1 10 Porous radius ( µ m) Delage et al., Géot. 2006 SAMPLE AT HIGHER WATER CONTENT AND LOWER SUCTION HAS MORE WATER LOCATED IN VERY SMALL PORES (< 35 nm)

As compacted Calcigel Total pore volume ρ d = 2 Mg/m 3 , w = 9%, s = 22.7 MPa Agus and Schanz, 2005

Oven drying, Calcigel clay OVEN-DRYING (s from 22 MPa to 1GPa) HAS LITTLE EFFECT ON MICROSTRUCTURE AND NANOPORES Oven-dried,w = 0%, s = 1 GPa Agus and Schanz, 2005

Hydration – swelling, Calcigel clay Hydrated and swollen w = 19%, s = 0 MPa SWELLING CONCERNS BOTH NANO PORES (< 3.5 nm) AND LARGE PORES (around 1 µ m) Agus and Schanz, 2005

Outline of the presentation • High level nuclear waste disposals • Microstructure issues in compacted bentonites and sand bentonite mixtures: • Hydration of compacted bentonites • Nanostructure issues during hydration 32

Saturated intra-aggregates swelling mechanisms Saiyouri, Hicher & Tessier (2000), using Pons et al. (1981) • X ray scattering at low angles • Probabilistic analysis Interlayer distances as a function of decreased suction

Water adsorption along smectites ����� �������������� � � ���� 4 layers : 20.6 Š���������������� ������������������ Sayiouri, Hicher & Tessier (2000)

Adsorption of water vs suction, MX 80 �� �������� ������������������� �������� �� 18.6 Š�������� 15.6 Š������� 12.6 Š�� 7 MPa 50 MPa � ����� ���� ��� � �� ��� ���� ������������ inside the ��� saturated aggregates Sayiouri, Hicher & Tessier (2000)

Hydration from a dry state inside the saturated aggregates possible double layer high suction (> 50 MPa) low suction (< 7 MPa) 100 layers 10 layers Sayiouri, Hicher & Tessier (2000)