HAL Id: hal-02417815
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Submitted on 18 Dec 2019
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Swelling properties of MX-80 bentonite materials for Andra’s repository engineered barriers
F. Bernachy-Barbe, C. Gatabin, C. Imbert, W. Guillot, J. Talandier
To cite this version:
F. Bernachy-Barbe, C. Gatabin, C. Imbert, W. Guillot, J. Talandier. Swelling properties of MX-80 bentonite materials for Andra’s repository engineered barriers. Beacon Initial Workshop, Jun 2017, Kaunas, Lithuania. Beacon Initial Workshop, 2017. �hal-02417815�
Objectives
Experimental results
Swelling properties of MX-80 bentonite materials for
Andra’s
repository engineered barriers
Nuclear Energy Division
Division for Saclay Nuclear Activities
Department of Physico-Chemistry
Service for Radionuclide Behavior Studies
Beacon Initial Workshop – Kaunas, Lithuania – 19 – 20
th
June 2017
F. Bernachy-Barbe, C. Gatabin, C. Imbert, W. Guillot
1
, J. Talandier
2
1Den-Service d’Etude du Comportement des Radionucléides (SECR), CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France 2Andra, 1-7 Rue Jean Monnet, F-92298 Chatenay Malabry, France
Macroscopic effect of concrete pore water on swelling properties
Residual local pressure heterogeneities
Swelling properties at different scales : the representative volume
70% diam. 32 mm pellets 30% Crushed pellets
DOPAS-FSS (full scale
seal) mock-up
Filling in progressFSS material :
MX-80 in
granular form
allows for an
easier setting
To the metric scale : REM experiment started 2015
• Hydration water from the COx is transported through concrete components
What is the effect of concrete water on the
swelling properties ?
• Low-pH concrete formulated at CEA to limit impact on bentonite properties • Swelling pressure characterized on small samples (1 pellet) and medium sized
(~18 pellets) saturated with :
- Site water from Meuse-Haute Marne URL borehole - Ordinary concrete synthetic pore water
- Low pH concrete synthetic pore water
• Sample diam. 1m, height 1m
• 1D hydration w/ synthetic site water
• 65 local sensors : 30 radial force and TH, 5 water pressure 0 1 2 3 4 5 6 7 0 100 200 Axial p ress ur e ( MP a) Time (days) 1.204 1.305 1.411 1.493 1.544 1.586
Constant volume swelling properties
Check that resaturation is attained at the metric scale Check swelling is globally homogeneous Evaluate hydromechanical properties at saturation (several decades !)
₋ Very similar swelling curves respectively to a material with a much larger volume element (relatively to the pellet size)
What are the resulting transport properties ?
• Method :
₋ Annular hydration of a larger size sample (~18 pellets) of representative density with ordinary concrete water
₋ Axial permeability test at saturation with site water
Concrete plug & lining Water Bentonite seal COx claystone Force sensor Displacement sensor Porous element Air outlet
Concrete pore water injection
Site water injection
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 10 100 S w e ll ing pre s s ure (M P a ) Time (days) FTP site water
Ordinary concrete water Low pH concrete water
Much lower swelling pressure at saturation
Strong reserves on the long-term swelling pressure stability
Much better behaviour with low-pH concrete water Decreasing effect with sample size ?
φ 57 mm, h 32 mm
φ 120 mm, h 56 mm
Identical swelling pressures reached for radial vs. axial hydration
Hydraulic conductivity ≈×10
Hypothesis : existence of a small sized region with reduced hydraulic properties
₋ Consistent with dependence to the sample volume ₋ Slower transport of responsible species ?
₋ Maybe a shortcut for water transport !
Q = kw.I.S vs. Sound zone Affected zone Radial Axial COx claystone Concrete
Heterogeneities at different scales :
Technological voids Chemical heterogeneities at interfaces Local density variations Global density gradient Pellet/powder bentonite seal
What is the representative volume element
to assess swelling properties of bentonite in
granular form ?
Is there an hydraulic performance loss due to
potential chemical interaction at boundaries
(concrete liners) ? Effect on macroscopic
mechanical response ?
What is the extent of local heterogeneities ?
Do they resorb through time ?
Some questions :
In a nutshell :
There is an hydraulic performance loss (×10 in present study) due to hydration with ordinary concrete
porewater, and the formulated low-pH concrete is effective in solving this issue. Mechanical effects are
small for large sample volumes.
0 1 2 3 4 5 6 7 1.2 1.4 1.6 Sw ell ing pr es su re (MP a) Dry density (g/cm3) Diam. 7 mm pellets + powder reference curve FSS material reference curve Time (days) Dry density (g/cm3) H yd rau lic con d u ct ivit y (m/ s) V olu me (c m 3) This test
REM mini-mock-up :
largest sample size
within reasonable lab.
time scales
• Hydration of φ 240 mm, h=105 mm sample (124 pellets)
• Radial force and THR sensors 20 30 40 50 60 70 80 90 100 0 50 100 150 200 % R el at iv e humi di ty Time (days) HR1 (%) HR2 (%) HR3 (%) HR4 (%) HR5 (%) • 1D in vapour phase ? 0 10 20 30 40 50 100 Pressure (bar) Time (days) P1 (bar) Z=20mm P3 (bar) Z=60mm P4 (bar) Z=80mm Pression axiale
• Local pressure heterogeneities ≈20%
• Low pressure consistent with low RH area • Pressure still increasing > 600 days
Local pressure
heterogeneities do not seem to resorb at short to medium time scales, but...
Is saturation really reached ?
Resaturation of a smaller sample at 1 then 45 bar
(in-situ pressure) injection shows no sign of local
rehomogenization
₋ Swelling kinetics for samples composed of 16-20 pellets
Is it a representative
volume ?
Time (days) Ef fect iv e p ressu re (ba r) Natural resaturation Pressurized injection Uncertainties on the effect of sample size on macroscopic response. What is the
effect of friction at walls ?
Local pressure heterogeneities are of order 20% and do not show signs of short
term decrease.
0 1 2 3 4 5 0 100 200 300 400 Sw ell ing pr es su re (M Pa) Time (days) Swelling kinetics obviously depend on sample thickness
Sample diameter seems to play a role : effect of friction at the cell boundaries ?
Local radial pressure more consistent
₋ Swelling kinetics as a function of sample dimensions
