This document summarizes coupled thermal-hydrological-mechanical (THM) modeling of in situ heater experiments at underground laboratories in Mont Terri, Switzerland and Bure, France. The modeling is done using the TOUGH-FLAC simulator to simulate complex THM processes during heating. Good agreement is shown between modeled and measured temperatures, pressures, and saturations. The modeling is being used to study buffer/rock interactions and upscale THM parameters from sample to repository scale.

1. Spent Fuel and Waste Science and Technology
Coupled THM modeling of In Situ Heater
Experiments at Mont Terri (Switzerland) and
Bure (France) Underground Laboratories
Jonny Rutqvist, Hao Xu, Jens Birkholzer
Lawrence Berkeley National Laboratory
SFWST WG Meeting in Las Vegas
Argillite/Crystalline Sessions
May 24, 2017

2. Spent Fuel and
Waste Science and
Technology
Stress-induced
fracture opening
or closure with
associated
permeability
change
Infiltration of
water from rock
to bentonite
Drying and
shrinkage
Heating of bentonite
and rock
Thermal
Stress
Wetting and
swelling of
bentonite
Vapor flow along
thermal gradient
away from heat
source
Stress-induced
fracture opening
or closure with
associated
permeability
change
Infiltration of
water from rock
to bentonite
Drying and
shrinkage
Heating of bentonite
and rock
Thermal
Stress
Wetting and
swelling of
bentonite
Vapor flow along
thermal gradient
away from heat
source
Bentonite 100%
Saturated with a
Swelling pressure
of  5 MPa
Temperature close
to ambient
Sealing of
fracture?
Remaining
“permanent”
changes in rock
properties (e.g.
irreversible
fracture shear)?
Restored hydrostatic
fluid pressure
Excavation
Disturbed
Zone (EDZ)
Bentonite 100%
Saturated with a
Swelling pressure
of  5 MPa
Temperature close
to ambient
Sealing of
fracture?
Remaining
“permanent”
changes in rock
properties (e.g.
irreversible
fracture shear)?
Restored hydrostatic
fluid pressure
Excavation
Disturbed
Zone (EDZ)
Short-Term THM Disturbance
(0 to 1000 years)
Long-Term Impact
(10,000 to 100,000 years)
• Strongest during early time (excavation, waste emplacement and thermal
peak), but may cause permanent changes that could impact long-term
performance.
• Complex, but can be analyzed with advanced numerical modeling supported
by lab and field experiments.
Coupled THM Processes and
Nuclear Waste Disposal

3. Spent Fuel and
Waste Science and
Technology
TOUGH2
Multiphase flow and
heat transport
FLAC3D
Geomechanics
•Linking two established codes (each
hundreds of users word-wide)
•Both codes continuously developed and
applied in their respective fields
•Large number of constitutive model
available and relatively easy to
implement new constitutive models
•First developed and applied in the Yucca Mountain Project (2000-2008)
for modeling high-temperature multiphase flow and geomechanics
•Modeling THM in bentonite and clay host rock (from 2010)
•Modeling THM in salt host rock (from 2013)
•Modeling of THM in deep borehole disposal…
TOUGH-FLAC Simulator:
(Rutqvist et al., 2002; Rutqvist 2011; 2017)
LBNL THM Modeling of Nuclear
Waste Disposal

4. Spent Fuel and
Waste Science and
Technology
THM driven buffer/rock interactions: 1) Delayed buffer resaturation due to low rock
permeability, 2) thermal-pressurization in rock affects pressure and stress evolution in buffer
Opalinus clay:
15% fluid saturated porosity
510-20 m2 permeability
 Strong THM coupling
COUPLED THM MODELING OF A
REPOSITORY IN CLAY
Rutqvist et al., (2014)

5. Spent Fuel and
Waste Science and
Technology
TOUGH-FLAC
1) Barcelona Basic Model (BBM)
A constitutive model for thermo-elasto-plastic
behavior of unsaturated soils (bentonite)
• Shear strength and stiffness depends on saturation ( or suction)
• Wetting-induced swelling or collapse strains
Deviatoric
(shear) stress
Suction
Netpressure(total
stresslessgaspressure)
Drying
Cam-clay yield
surface (fully
fluid saturated)
Deviatoric
(shear) stress
Suction
Netpressure(total
stresslessgaspressure)
Drying
Cam-clay yield
surface (fully
fluid saturated)
Bentonite block stored at different
relative humidity (Teodori et al 2011)
55%
75%
99%
2) Barcelona Expansive Model (BExM)
• Micro- and macro-structure
• Proper modeling of fluid flow through macro pores and their
changes with stress and saturation
• Can provide a link for coupling mechanics with chemistry
TOUGH-FLAC THM Simulator
LBNL THM Model Developments
for Bentonite Backfill

6. Spent Fuel and
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Technology
 Undertaken by NAGRA as an ultimate test
for the performance of geologic disposal
in Opalinus Clay, with focus on both the
EBS components and the host-rock
behavior
 It will be one of the largest and longest
running heater tests worldwide
 Thousands of sensors within the EBS and
surrounding rock for monitoring THMC
processes
(Figure from Tobias Vogt NAGRA)
2.5 m
Mont Terri Full-scale Emplacement (FE)
Experiment
International Partners

7. Spent Fuel and
Waste Science and
Technology
TOUGH-FLAC Model of FE Experiment
Access tunnel
Plug
Heaters
Heater
Bentonite
blocks
Bentonite
pellets
Shot crete

8. Spent Fuel and
Waste Science and
Technology
• Anisotropic THM properties (thermal conductivity, permeability, strength)
of Opalinus Clay considering bedding
• TH bentonite properties of granular bentonite and bentonite blocks
from laboratory scale and HE-E (half-scale) modeling
• Basic Barcelona Model (BBM) properties for granular bentonite and
blocks (but too early to see significant swelling stress in the buffer)
THM Properties and Heat Load

9. Spent Fuel and
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Technology
Heater
Host
rock
Moisture Flow in Bentonite Buffer
During Heating
Heating
Drying
Wetting
 zP
k
X ll
l
rlw
ll
w
l  g
k
q 


Liquid Darcy Flow:
Liquid pressure
gradient
w
g
w
ggg
w
g XDS  Ii 
Vapor diffusion:
Water mass
fraction in gas
Effective
vapor diffusion

10. Spent Fuel and
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Technology
T IM E (d a y s )
TEMPERATURE(C
o
)
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
1 2 0
1 3 0
1 4 0
1 5 0
H e a te r S u rfa c e
1 0 c m fro m h e a te r
2 0 c m fro m h e a te r
A t tu n n e l w a ll
F ie ld d a ta
M o d e lin g
TIME (days)
TEMPERATURE(Co
)
0 50 100 150 200 250 300 350 400
0
50
100
150
Heater surface
10 cm from heater
20 cm from heater
Simulated and Observed Temperature
(mid heater) 1st year
• Calibrated thermal properties of “heater” for temperature distribution on heater-
surface
• Heater-surface temperature higher at granular bentonite (Tmax=126C) then at
bentonite block pedestal (Tmax=118C)
• Excellent agreement between simulated and observed temperature
Granular Bentonite Bentonite Blocks

11. Spent Fuel and
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Technology
TIME (days)
RELATIVEHUMIDITY(-)
0 50 100 150 200 250 300 350 400
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
20 cm from heater
10 cm from heater
At tunnel wall
20 cm from heater
10 cm from heater
TIME (days)
RELATIVEHUMIDITY(-)
0 50 100 150 200 250 300 350 400
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
• Good agreement for substantial reduction of the effective vapor diffusion
coefficient through a medium tortuosity factor as low as 0.14.
w
g
w
ggg
w
g XDS  Ii 
Diffusion coefficient for vapor-
air mixture 2.13e-5 m2/s
Medium tortuosity,
best match for 0.14
Mass fraction
Simulated and Observed Moisture
Evolution (mid heater) 1st year

12. Spent Fuel and
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Technology
TIME (days)
TEMPERATURE(Co
)
0 100 200 300 400 500 600 700 800
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
Heater Surface
10 cm from heater
20 cm from heater
At tunnel wall
Field data
Modeling
20 cm from heater
10 cm from heater
At tunnel wall
TIME (days)
RELATIVEHUMIDITY(-)
0 100 200 300 400 500 600 700 800
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Comparison with 2 Years of Data
(Heater 2)
Heater 2

13. Spent Fuel and
Waste Science and
Technology
Comparison with 2 Years of Data
(Heater 3)
TIME (days)
RELATIVEHUMIDITY(-)
0 200 400 600 800
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
20 cm from heater
10 cm from heater
At tunnel wall
Field data
Modeling
TIME (days)
TEMPERATURE(Co
)
0 200 400 600 800
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
Heater Surface
10 cm from heater
20 cm from heater
At tunnel wall
Heater 3

14. Spent Fuel and
Waste Science and
Technology
Real Tunnel Shape vs Model
Blue line at
designed tunnel
radius of 1.4 m
Laser scan
of tunnel wall

15. Spent Fuel and
Waste Science and
Technology
Température
Pression
interstitielle
3 Borehole Heaters 12
to 16 m from drift wall
23 monitoring boreholes with
over 200 sensors (temperature,
pressure, displacement)
Temperature
Pressure
TED Borehole Heating Experiment at Bure
by ANDRA, France

16. Spent Fuel and
Waste Science and
Technology
Sample
scale
Borehole
scale
Micro-tunnel
scale
Repository
scale
• Upscaling is an important issue for the repository design and safety
calculation: How to go from sample to a repository scale ?
• Two in situ tests performed at the underground research laboratory in
Bure (France) will be interpreted and modeled
• The host rock consists of Callovo-Oxfordian claystone (COx)
• Thermally induced pore pressure build-up and stress changes around a
repository…
Upscaling of THM Parameters
(DECOVALEX Task Led by ANDRA, France)

17. Spent Fuel and
Waste Science and
Technology
TOUGH-FLAC Model of TED Borehole
Heating Experiment
Entire Model
Heaters
(Biot’s coefficient)
Some basic
Cox Claystone
properties

18. Spent Fuel and
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Technology
Simulation Results with Comparison to
Measured Data - Temperature

19. Spent Fuel and
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Field Data
(dashed lines)
Simulations
(solid lines)
Simulation Results with Comparison to
Measured Data - Pressure

20. Spent Fuel and
Waste Science and
Technology
Concluding Remarks THM Modeling
• 3 new journal papers published on DECOVALEX-2015 work
(modeling of Mont Terri experiments)
• Continue modeling of FE- Experiment with access to field data
(2 years of heating)
- Opportunity for applying dual-structure (BExM) model in
collaboration with the Barcelona group
• Continue work on ANDRA’s heater tests in Cox clay stone
associated with DECOVALEX-2019
• Implementation and testing of continuum damage model for
EDZ and permeability evolution in clay host rock with
comparison to TOUGH-RBSN discrete fracture model…
20