The document summarizes modeling work on the thermal-hydrological-mechanical (THM) behavior of salt barriers for nuclear waste repositories. It discusses: 1) Development of a coupled THM model using TOUGH-FLAC to simulate compaction, brine flow, and borehole closure. 2) Initial modeling of small-scale borehole experiments, showing temperature effects on pressure changes and borehole closure. 3) Plans for further model verification, validation against field data, and application to analyze brine release mechanisms in the borehole experiments.

1. Spent Fuel and Waste Science and Technology
Jonny Rutqvist, Mengsu Hu, Laura Blanco-Martin, Jens Birkholzer
Lawrence Berkeley National Laboratory
SFWST WG Meeting in Las Vegas
International Session
May 23, 2017
THM Modeling of the Borehole Tests

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Waste Science and
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Modeling activities at LBNL
Crushed salt backfill
(geotechnical barrier)
Waste package
Rock salt
(geologic barrier)
Modeling:
• Understanding of individual
processes (infiltration,
compaction, …)
• Predicting the long-term integrity
of the barriers
Initial
crushed salt
porosity ~ 30-35 %
Effect of brine precipitation
& dissolution
(host rock, backfill)
Crushed salt
reconsolidation process
Damage and healing of
the host rock (EDZ)
Fluid infiltration if
s3 +P > Pcrit
Heat source, gas source
(corrosion)
• Coupled THMC processes

3. Spent Fuel and
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Salt Coupled THM Processes – TOUGH-FLAC
 Lux/Wolters solid salt constitutive model (creep, TM damage-induced permeability
(DZ), high pressure fluid filtration, sealing, heating)
 Crushed salt constitutive model (THM properties as a function of compaction and
solidification)
 Large-strain and deformable mesh
 Brine migration, evaporation, condensation, salt precipitation etc. (THMC)

4. Spent Fuel and
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FY17 Status and Plan
 Two peer-reviewed journal papers published
– Blanco-Martin et al. (2017) “Extension of TOUGH-FLAC to the finite strain
framework. Computers & Geosciences (In press, 2017),
http://dx.doi.org/10.1016/j.cageo.2016.10.015
– Blanco-Martín et al. (2016) “Thermal–hydraulic–mechanical modeling of a large-
scale heater test to investigate rock salt and crushed salt behavior under repository
conditions for heat-generating nuclear waste” Computers and Geotechnics.
 Developed continuum model for brine-inclusion migration
– Important for modeling brine-inflow mechanisms at small scale borehole test
 Code verification of sequential coupling for strong THM coupling
– Important for THM-induced brine-inflow at small scale borehole test
 Updated repository compaction and sealing modeling
– Using Asse Mine in situ calibrated creep parameters (at low deviatoric stress)
 THM modeling of small borehole experiment (ongoing)
– Focus on investigating THM mechanisms of brine-release (intergranular, intragranular (brine-
inclusions), thermal pressurization, damage-induced)
– Borehole closure at WIPP (creep parameters for WIPP using historic WIPP closure data)
– Predicting borehole closure for small borehole experiment Test 1 and Test 2
Further verification, validation, publications and application to borehole test:

5. Spent Fuel and
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2D model
Updated Long-term Compaction and
Sealing Modeling Using In Situ Data
Using Asse Mine in situ calibrated creep
parameters (at low deviatoric stress)
100 years to less
than 2% porosity
Earlier laboratory determined creep parameters
overestimated the rate of drift closure

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Borehole Closure THM Modeling
 Lux-Wolters constitutive model (creep) parameters for WIPP
salt?
 Alternative use of WIPP-reference (creep) constitutive model that
is readily available in standard FLAC3D simulator
 Testing and in situ calibration against historic WIPP borehole
closure and strain data (non-heated and heated)
– Room A and B vertical boreholes in room floors (axial and
tangential strain data)
– Room Q convergence data (2.9 m diameter tunnel)
– Intermediate Scale Borehole Test (0.91 m diameter)

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20.7
12.4
Modeling Intermediate Scale Borehole Test
(0.91 m diameter)
WIPP-reference Creep
Model Parameters
Original Fig 5 and 6 from Munson et al., 1994 Int J. Rock Mechanics..

8. Spent Fuel and
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Initial TH and THM Modeling of
Small Borehole Test
Temperature Duration Simulation Scenarios
Test 1 Ambient (30°C) 200 days • TH
• THM with WIPP model
Test 2 120°C 100 days • TH
• THM with WIPP model
Properties Value
Porosity 1%, 0.2%
Permeability 1e-22m2
Young’s modulus 20GPa
Poisson ratio 0.3
WIPP
constants
Value
a 4.56
b 127
d 5.79e-36
e 5.39e-8
n 4.9
Gas
constant
1.987
Simulation settings

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TH simulation results for Test 1
Impact of intergranular porosity (0.2 to 1%)
Initial pressure assumed to be 12 MPa (lithostatic stress is 15 MPa)

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Measured Pressure Distribution
Around Caverns at WIPP

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THM simulation results for Test 1- x displacement
After excavation 1 h
1d 200d

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TH simulation results for Test 2

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THM simulation results for Test 2- x displacement
After excavation 1 h
1d 100d

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THM simulation results for Test 2
Borehole closure (radius change)

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THM simulation results for Test 2
Sigma x: After excavation
Sigma y: After excavation
Sigma x: 100d
Sigma y: 100d

16. Spent Fuel and
Waste Science and
Technology
FY17 Status and Plan
 Two peer-reviewed journal papers published
– Blanco-Martin et al. (2017) “Extension of TOUGH-FLAC to the finite strain
framework. Computers & Geosciences (In press, 2017),
http://dx.doi.org/10.1016/j.cageo.2016.10.015
– Blanco-Martín et al. (2016) “Thermal–hydraulic–mechanical modeling of a large-
scale heater test to investigate rock salt and crushed salt behavior under repository
conditions for heat-generating nuclear waste” Computers and Geotechnics.
 Developed continuum model for brine-inclusion migration
– Important for modeling brine-inflow mechanisms at small scale borehole test
 Code verification of sequential coupling for strong THM coupling
– Important for THM-induced brine-inflow at small scale borehole test
 Updated repository compaction and sealing modeling
– Using Asse Mine in situ calibrated creep parameters (at low deviatoric stress)
 THM modeling of small borehole experiment (ongoing)
– Focus on investigating THM mechanisms of brine-release (intergranular, intragranular (brine-
inclusions), thermal pressurization, damage-induced)
– Borehole closure at WIPP (creep parameters for WIPP using historic WIPP closure data)
– Predicting borehole closure for small borehole experiment Test 1 and Test 2
Further verification, validation, publications and application to borehole test:

17. Spent Fuel and
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Verification TOUGH-FLAC Sequential
Algorithm for Strong Pore-Volume Coupling
 Terzaghi Consolidation
 Mandel's Problem: Squeezing fluid out
of the porous rock
 Booker and Savvidou's problem:
Thermally-driven pressure changes
and THM induced deformation

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THM simulation results for Test 1
Borehole closure (radius)

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THM simulation results for Test 1
Sigma x: After excavation
Sigma y: After excavation
Sigma x: 200d
Sigma y: 200d

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Components
Primary
continuum
Secondary
continuum
Coupling
Salt
Darcy`s law
Fick`s law
Brine migration law Brine migration-related salt
migration flux as a sink/source
Water
Darcy`s law
Fick`s law
Brine migration law Brine migration flux as a
sink/source
A dual-continuum model for analyzing salt migration

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21
A new FVM model for mechanical analysis