saturation of barrier materials under thermal gradient · final dry density (g/cm 3) mx-80,...
TRANSCRIPT
International Symposium on Energy Geotechnics
Saturation of barrier materials under thermal gradient
M.V. Villar, P.L. Martín, F.J. Romero, R.J. Iglesias, V. Gutiérrez-Rodrigo
Barcelona, June 3rd, 2015
�FRAMEWORK
�THE HE-E EXPERIMENT
�AIMS
�MATERIALS
�TH TESTS IN CELLS
�ONLINE RESULTS
�POSTMORTEM RESULTS
OUTLINE
Saturation of barrier materials under thermal gradi ent
Saturation of barrier materials under thermal gradi ent
FRAMEWORK: GEOLOGICAL DISPOSAL OF NUCLEAR WASTE
Waste canisters Engineered barrier
Concrete plug • Swelling capacity
• Low permeability
• Retention capacity
Bentonite-based materials are
proposed as sealing/backfilling
material in underground
repositories (engineered barrier)
THE HE-E EXPERIMENT
• Located at the Mont Terri URL (Switzerland) in a 50-m long non-lined horizontal
microtunnel of 1.3 m diameter excavated in 1999 in the shaly facies of the
Opalinus Clay. Characterised during the Ventilation Experiment
• 1:2 scale heating experiment considering natural resaturation of the EBS
• Heaters supported by MX80 bentonite blocks (ρd=1.81 g/cm3, w=10.3%)
• Granular material filling the rest of the gallery
THE HE-E EXPERIMENT
Two symmetrical sections, with different sealing materials
•MX-80 bentonite pellets (B) (ρd=1.46 g/cm3, w=5.9%)
•65/35 sand/bentonite mixture (S/B) (ρd=1.5 g/cm3, w=4%)
Maximum heater surface temperature of
140°C, increased almost linearly to its
maximum value in a period of 1 year
Natural hydration
AIMS
• Reproduce in the laboratory the conditions of the granular
material of the HE-E in situ test to provide support for its
modelling
• Check the thermo-hydro-mechanical behaviour of the HE-E
materials at T>100°C
• Compare the THM behaviour of two different sealing
materials
MATERIALS
0
10
20
30
40
50
60
70
80
90
1 00
0 .010 .111 0
D iam eter (m m )
Pe
rce
nta
ge
pa
ssin
g
B
S/B
MX-80 BENTONITE PELLETS
Specific heat capacity: 0.64 J/g·K (at 22°C) - 0.97 J/g·K (at 115°C)
Thermal conductivity: 0.12 W/m·K
Grain density: 2.75 g/cm3
BET as= 33 m2/g
SAND/BENTONITE
MIXTURE
Grain density: 2.71 g/cm3
BET as= 5 m2/g
Thermal conductivity: 0.33 W/m·K
Specific heat capacity: 0.74 J/g·K (at 22°C) - 0.90 J/g·K (at 115°C) Dry sieving
MATERIALS
0
10
20
30
40
50
60
70
80
90
100
1101001000100001000001000000
Incr
emen
tal
po
re v
olu
me
per
gra
m (
%)
Pore diameter (nm)
S/B
B
MACROPOROSITY MESO
PORE SIZE DISTRIBUTION BY MIP
Cl- SO42- HCO3
- Mg2+ Ca2+ Na+ K+ Sr+ pH
10636 1354 26 413 1034 5550 63 47 7.6
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1 1.2 1.4 1.6
Sw
elli
ng
pre
ssu
re (
MP
a)
Final dry density (g/cm3)
MX-80, deionised water
S/B mixture, deionised water
S/B mixture, Pearson water
ln Ps = 5.44 ρd – 6.94
SWELLING PRESSURE TEST IN STANDARD OEDOMETERS
(SMALL SAMPLES)
kw MX-80 (1.5 g/cm3) = 4·10-13 m/s
kw S/B (1.4 g/cm3) = 2·10-10 m/s
Pearson water composition (mg/L)
THM TESTS IN CELLS
THM TESTS IN CELLS
TESTS CHARACTERISTICS
Material: HE-E sand/bentonite (65/35)
mixture, MX-80 pellets
Height of column: 50 cm
Initial dry density and water content: 1.46
g/cm3 and 3.6%, 1.52 g/cm3 and 6.4%
Heater T bottom: 100°C – 140°C
Upper T: room
Hydration: Pearson water, 0.06 bar
Data provided: online measurements of
RH, T, water intake, heater power, axial
pressure
MX-80 pellets
1 5
2 0
2 5
3 0
3 5
4 0
4 5
5 0
5 5
6 0
0 1 000 2 000 30 00 400 0 5000
T im e (h)
Te
mp
era
ture
(°
C)
T 1 T 2
T 3 lab
1 00° C 1 40° C
ONLINE RESULTS: HEATING PHASE
Quick thermal steady state
Low temperatures in thematerial due to its low thermalconductivity and heat losses
16
21
26
31
36
41
46
51
56
0 1000 20 00 3000 40 00
T im e (h)
Te
mp
era
ture
(°
C)
T 1 T 2
T 3 lab
100°C 140°C
S/B mixture
S/B mixture
ONLINE RESULTS: HEATING PHASE
20
30
40
50
60
70
80
90
0 1 000 2000 3000 4000
T im e (h)
Re
lati
ve
hu
mid
ity
(%
)
RH 1
RH 2
RH 3
100°C
140°C
2 0
3 0
4 0
5 0
6 0
7 0
0 100 0 2 000 3000 400 0 50 00
T im e (h)
Re
lati
ve
hu
mid
ity
(%
)
RH 1
RH 2
RH 3
100° C 140° C MX-80 pellets
Quick movement of thevapour phase towards coolerareas
Much longer time forhydraulic steady state
Heating phase: steady values
Higher T and heater power in B pellets cell:
• Steel reinforcement
• Better thermal contact with heater
ONLINE RESULTS
15
30
45
60
75
90
105
120
135
20
30
40
50
60
70
80
90
0 20 40Te
mp
era
ture
(°
C)
Re
lati
ve
hu
mid
ity
(%
)
Distance from heater (cm)
HEATER T 140°C
RH B
RH S/B
T B
T S/B
For ρd ≈ 1.5 g/cm3
Faster vapour movement in cell S/B:
• Higher gas permeability
• Lower retention capacity
0
50
100
150
200
250
300
350
400
10
20
30
40
50
60
70
80
90
100
0 10000 20000 30000
Wa
ter in
tak
e (g
)
Re
lati
ve
hu
mid
ity
(%
)
Time hydration (h)
RH1 RH2
RH3 water
MX-80 pellets: heating + hydration phase
ONLINE RESULTS
w=18.8%, Sr=65%
15
20
25
30
35
40
45
50
55
60
0 5000 10000 15000 20000 25000 30000
Tem
pe
ratu
re
(°C
)
Time hydration (h)
T1 T2
T3 lab
0
1
2
3
4
5
6
7
8
0
50
100
150
200
250
0 2000 4000 6000 8000
Axi
al
pre
ssu
re (
MP
a)
Wa
ter
inta
ke
(cm
3)
Time (h)
MGR18
water intake
pressure
0
50
100
150
200
250
300
350
400
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 10000 20000 30000
Wa
ter in
tak
e (g
)
Ax
ial
pre
ssu
re (
MP
a)
Time hydration (h)
pressure
water
Expected equilibrium Ps 5 MPa (deionised water)
ONLINE RESULTS
MX-80 pellets: heating + hydration phaseSr=65%
Isothermal, deionised water, 10 cm high
15
25
35
45
55
65
0.01 1 100 10000
Tem
pe
ratu
re
(°C
)
Time hydration (h)
T1 T2
T3 lab
20
30
40
50
60
70
80
90
100
0.01 1 100 10000
Time hydration (h)
Re
lati
ve
hu
mid
ity
(%
)
30
130
230
330
430
530
630
730
830
930
1030
Wa
ter
inta
ke
(g
)
RH1
RH2
HR3
water
Sand/bentonite mixture: heating + hydration phase
ONLINE RESULTS
Sand/bentonite mixture: heating + hydration phase
ONLINE RESULTS
20
30
40
50
60
70
0 2 4 6 8
Tem
pe
ratu
re
(°C
)
Distance to axis (cm)
40 cm
22 cm
10 cm
Distance from heater
S/B mixture Teflon Rockwool
Average T, but they tend to decrease
9
10
11
12
13
14
15
10
20
30
40
50
60
70
0 10000 20000 30000
He
ate
r p
ow
er
(W)
Tem
pe
ratu
re
(°C
)
Time hydration (h)
T3 Lab T power
DISMANTLING CELL SAND/BENTONITE
DISMANTLING CELL SAND/BENTONITE
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50
Distance to hydration surface (cm)
Wa
ter
con
ten
t (%
)
1.30
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
Dry
de
nsi
ty (
g/c
m3)
w.c.
d.d.
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50
Distance to hydration surface (cm)D
eg
ree
of
satu
rati
on
(%
)
Actual water intake: 676 g
Online measurement: 887 g
Final w = 28.2%
Dry density = 1.46 g/cm3
Average w = 28.3%, ρd = 1.44 g/cm3, Sr = 93%
POSTMORTEM RESULTS CELL SAND/BENTONITE
0
10
20
30
40
50
60
70
80
90
100
1101001000100001000001000000
Incr
em
en
tal
po
re v
olu
me
pe
r g
ram
(%
)
Pore diameter (nm)
1 9
17 25
33 41
47 49
original
MACROPOROSITY MESO
Distance from hydration surface (cm)
POSTMORTEM RESULTS CELL SAND/BENTONITE
0
5
10
15
20
25
1.0E+04
1.0E+05
1.0E+06
0 10 20 30 40 50
Me
sop
ore
mo
de
(nm
)Ma
cro
po
re m
od
e (
nm
)
Distance from hydration surface (cm)
macro
meso
macro
meso
Sample Macropores (>50 nm), %
Mode macropores, µm
Mesopores(50-7 nm), %
Mode mesopores, nm
Micropores (<7 nm), %
Original 92 204 8 19
Sections 1-23 a 83±6 58±21 5±1 16±4 12±7
Section 24 b 53 110 8 18 39
POSTMORTEM RESULTS CELL SAND/BENTONITE
Ca-Na sulphates
NaCl
Close to heater
SEM OBSERVATIONS
CONCLUSIONS
� Low thermal conductivity of the dry materials and heat losses: steep
thermal gradient and lower temperatures than in in situ test
� The different gas and water permeabilities of both materials implied:
• Different pace and extent of water redistribution in the vapour
phase: different relative humidity gradient at the end of the heating
phase
• Faster hydration and quicker dissipation of the water content
gradient for test with S/B mixture
CONCLUSIONS
CELL B
• During heating phase, axial pressure was related to temperature,
afterwards to hydration state
• Probably non-monotonic development of swelling pressure in pellets
CELL S/B
• The arrival of the water front implied a sudden increase in temperature
for S/B mixture, and an overall soft decrease of T after saturation
• The S/B 50-cm long column was completely saturated after 2.8 years of
hydration
• Water content, dry density, degree of saturation and pore size
distribution were homogeneous along the S/B column, except in the 2
cm closest to the heater
The research leading to these results received funding from the European Atomic Energy Community's Seventh
Framework Programme (FP7/2007-2011) under grant agreement n°249681 and was additionally financed by
ENRESA through a CIEMAT-ENRESA General Agreement.
It is being currently financed by the Mont Terri Consortium