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

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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

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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.