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7th US/German Workshop on Salt Repository Research, Design, and Operation
Presenter: Sandra FahlandBGR, Hannover, Germany
Washington, DCSeptember 7-9, 2016
Further Important Topics in Rock Salt Geomechanics – State 2016
Repositories in salt formations - present and future work related to integrity analyses
Geomechanical integrity analysis of the repository is a main topic of performance assessment 3 main salt related topics have been identified (5th US-German Workshop 2014)
(1) how salt deforms in the long term(2) integrity analysis of rock salt barrier(3) consolidation of crushed salt
2
Progress in 2015/16 Reminder on issues still pending New topics
Salt – barrier properties
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crushed salt backfill -photo
Intact rock salt EDZ Crushed salt backfill
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The challenge … how does salt behave in the long term?
Boundary conditions:Forecast period: 103 < time (years) < 106
Deformations: 0.1 < ε < 1Deformation rates: 1∙10-17 < ε (1/s) < 3∙10-11
Temperatures: 20°C - 200°C
Experimental database Creep experiments at small deviatoric
stresses - Berest (SMRI): uniaxial creep test - BGR: running (>1 y now)- IfG: long tests are started / a high
resolution creep test rig is under construction
EU Project DOPAS – LASA EDZ: Experimental data related to salt/concrete interfaces (GRS)
Currently pending Assessing the suitability of the
constitutive laws by recalculating failure events ( KOSINA)
Forthcoming topics "Relaxation" Pressure solution creep
˙
Modelling the salt barrier behavior (THMC)• BMWi Joint Project „Comparison of current
constitutive models for rock salt“ (2004 – 03/2016) • BMWi Joint Project WEIMOS „Further development
and qualification of the rock mechanical modelling for the HLW disposal in rock salt“ (WEIMOS), started April 2016 - Partners: AH, IfG, IUB, TU-BS, TUC, SNL
• Creep at small deviatoric stresses• Tensile stress• Healing of damage: influence pT• Influence of inhomogeneities (e.g. interfaces)
Presentation A. Hampel
Presentation K. Wieczorek
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Rock salt deformation behavior at small deviatoric stresses
BGR (2016)
Varangeville - Berest et al. (2015): Avery Island salt
Dead weight setup
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Natural analogues – closing the gap?
3D-simulation of salt dome uplift
Subgrain – paleostress analysis
"dry" salt dome
• In different salt structures, deformation mechanisms and rheology may be different.
• Microstructure analysis is required to study deformation mechanisms, paleostress and paleorheology.
• Numerical modelling allows demonstration.
"humid" bedded salt
"wet" salt glacier
Residual stress?
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Subgrain – paleostress analysis; Gorleben salt dome, Germany
subgrains and paleostresses in halitic rocks in central part of salt dome (Hauptsalz, Staßfurt-Series, z2HS)
(Hammer et al. 2015, Thiemeyer et al. 2016)
subgrains and paleostresses in halitic rocks near intensively deformed anhydrite rocks in salt dome (Anhydritmittelsalz, Leine-Series, z3AM)
(Mertineit et al. 2015)
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The WEIMOS approach: High-resolution creep rig of IfG
Axial force: 200 kN
Sample size: = 60mm, l = 120mm
Capacitive displacementsystem
Quartz rod
CSH02FL-CRm1,4Resolution 0.15 nmLinearity 0,05 mTemperature sensitivity
-2.4 nm/°C
Measuring principleThe principle of capacitive displacement measurement using the capaNCDT (capacitive Non-Contact Displacement Transducer) system is based on how an ideal plate-type capacitor operates. The two plate electrodes are represented by the sensor and the opposing measurement object.
Pc-max: 32 MPaTmax: 120°C
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Integrity of the salt barrier
Criteria to assess integrity are decisive to prove effectiveness of salt barrier’s safety function
Present status dilatancy criterion
(isotropic) minimum stress/fluid
pressure criterion (isotropic)
Under consideration load-dependent dilatancy criterion
(BGR) anisotropic fluid pressure criterion,
directional infiltration (THM process) - TUC/IfG/BGR/DBETEC
The dihedral angle – An additional percolation threshold? Science paper „Deformation-assisted fluid percolation in rock salt“ by S. Ghanbarzadeh et al.
DAEF – statement April 2016 Break-out-session US/German
Workshop 2016 KOSINA: Percolation tests at high
pT cond. (-100 MPa/120°C)
First steps/pending discontinuum
approaches DBETEC, IfG
Fully coupled thermo-hydro-mechanical simulations TUC, IfG
Forthcoming topics additional (hypothetical)
failure modes TUBS, DBETEC
influence of residual stresses
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Additional (hypothetical) failure modes
Isotropic fluid pressure criterion σmin > pfl
using effective stresses (Terzaghi)σ‘min = σmin – pfl > 0σmin = σ3 least principal stresspfl = hypothetical hydraulic pressureσ‘min = σ‘3 effective least principal stress
Isotropic dilatancy criterion (Christescu/Hunsche)τzul/σ* = a ∙ (σm/ σ*)² + b ∙ (σm/ σ*)using effective stresses (Terzaghi)τ‘zul/σ* = a ∙ (σ‘m/ σ*)² + b ∙ (σ‘m/ σ*)τ octahedral shear stressσm mean stressσ* scaling factorτ‘ effective octahedral shear stressσ‘m = (σ1 + σ2 + σ3 – 3pfl)/3 effective mean stress
properties of a viscous solid properties similar to a suspension vs
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Crushed salt consolidation
Current knowledge gives confidence that granular salt will compact to a final porosity in the order of 1±1 % within less than 1000 a,but this has to be demonstrated reliably
Experimental investigations
REPOPERM II long-term tests (4 y) finished (GRS, final report in preparation)
Long-term compaction tests (up to 10 y), BGR develops a new experimental setup
Crushed salt backfill in-situ consolidation state re-investigated after 15 y in the framework of the Asse site investigations (IfG)
State of constitutive models
DAEF initiative on crushed salt behavior is established
First results2-phase-flow (to appear, GRS)
PendingNatural analogues
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Salt consolidation lab experiments in the REPOPERM project
(raw
data
)
brineinjection
REPOPERM II Multistep load tests, different initial solution contents, varying temperature, later flooding
characterization after dismantling yields porosities of 1 – 2%
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Revisitation of the BAMBUS site – part of Asse site investigations
Backfill compaction proceeds: Within 15 years, a further reduction of backfill porosity by 3 – 5% is observed ( drift convergence at the 800‐m‐level).
The backfill is very dry.
Aim of investigations Evaluation of the backfill properties Better assessment of stabilization
measures in the Asse repository
Texture and lab investigations were performed by Sandia (Hansen, 2016)
• Porosity: 23 – 17%• Thermal conductivity: 2.3 W/m∙K• Gas permeability: ca. 5 ∙ 10-13 m2
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DAEF initiative on crushed salt consolidation
Partners: GRS, BGR, DBETEC, IfG, TUC
Participation of the US-colleagues is highly desirable
Current knowledge gives confidence that granular salt will compact to a final porosity in the order of 1±1 % within less than 1000 a, but this has to be demonstrated reliably!
Work topics• Classification of the available experimental data
sets:- reliability in the low porosity range - suitability for model calibration
• Recommendations for completing the data base• Comparison of available constitutive models• Development of a strategy for calibration, bench
marking and improvement of models
Work schedule Presentation at the DAEF-Workshop 2016 Summary (NEA) report until 10/2016 Preparation of an US/GERMAN joint project
proposal until the end of the year
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Summary
Repositories in salt formations - present and future work related to integrity analyses
Geomechanical integrity analysis of the repository is a main topic of PA 3 main salt related topics have been identified (5th US-German Workshop 2014)
(1) how salt deforms in the long term(2) integrity analysis of rock salt barrier(3) consolidation of crushed salt
Progress in 2015/16 and remaining open issues
Ongoing key activities
• BMWI - Joint Project (WEIMOS), started April 2016Several experiments are already running or planned
• Percolation – experimental proof at repository conditions• DAEF initiative on crushed salt behavior established - US/German collaboration discussed
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AcknowledgementsMany thanks…
…to all colleagues and participating organizations
for their contributions
and BMUB and BMWi and their related organizations for their financial support.
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