CH/HM coupled behaviour of shaft sealing materials

Oliver Czaikowski, Kyra Jantschik, Helge C. Moog, Klaus Wieczorek & Chun-Liang Zhang GRS , Germany

• National shaft sealing concept • GRS activities within DOPAS • Available sealing material • Coupled material behaviour

– Damage induced permeability – Chemical long-term stability – Hydraulic sealing capacity

• Conclusions and further R&D work • Acknowledgements

Contents

National shaft sealing concepts

Reference conceptual design for the German shaft seal. The Gorleben-Bank is a folded anhydrite layer in the rock salt (Müller-Hoeppe et al. 2012a).

German disposal concept • Multiple barrier system consists of technical (disposal

container), geotechnical (sealing elements) and geological (host rock) barriers.

• Barriers shall prohibit intrusion of saline brines to the radioactive waste.

GRS-247

• Investigation of chemical-hydraulic behaviour of cement based sealing materials in rock salt (LAVA)

– Batch experiments with crushed concrete suited to investigation of water-rock interactions. – In-diffusion experiments with concrete and brine in order to determine the rate of alteration of the porous matrix. – Experiments with concrete brine at the contact with the EDZ in order to determine the rate of alteration of the sealing material owing

to advective flow at the boundary to the rock formation. – Accompanied by numerical modelling activities. – Deliverable D3.29

• Investigation of hydro-mechanical behaviour of cement based sealing materials in rock salt (LASA)

– Multistep creep tests on samples of concrete for the determination of creep parameters. – Triaxial compression tests on samples of concrete with axial flow of gas for determination of time-dependent compaction and damage

evolution. – Experimental long-term simulations of the systems rock salt / concrete using large hollow salt cylinders filled with concrete under

varying isostatic load and constant brine pressure. – Accompanied by numerical modelling activities. – Deliverable D3.31

• Hydro-mechanical behaviour of claystone-bentonite-mixture as seal material (THM-Ton) – Investigations on the long-term behaviour of the clay rock (Ucc, TCc, gas flow, swelling properties). – Experiments to characterize the geotechnical properties of compacted claystone-bentonite-mixtures as sealing material (water

retention curves, water re-saturation, water permeability and gas migration, swelling capacities). – Accompanied by numerical modelling activities. – Deliverable D3.32

GRS activities within DOPAS/ELSA

• Investigation of chemical-hydraulic behaviour of cement based sealing materials in rock salt (LAVA)

– Batch experiments with crushed concrete suited to investigation of water-rock interactions. – In-diffusion experiments with concrete and brine in order to determine the rate of alteration of the porous matrix. – Experiments with concrete brine at the contact with the EDZ in order to determine the rate of alteration of the sealing

material owing to advective flow at the boundary to the rock formation. – Accompanied by numerical modelling activities. – Deliverable D3.29

• Investigation of hydro-mechanical behaviour of cement based sealing materials in rock salt (LASA)

– Multistep creep tests on samples of concrete for the determination of creep parameters. – Triaxial compression tests on samples of concrete with axial flow of gas for determination of time-dependent compaction and

damage evolution. – Experimental long-term simulations of the systems rock salt / concrete using large hollow salt cylinders filled with concrete under

varying isostatic load and constant brine pressure. – Accompanied by numerical modelling activities. – Deliverable D3.31

• Hydro-mechanical behaviour of claystone-bentonite-mixture as seal material (THM-Ton) – Investigations on the long-term behaviour of the clay rock (Ucc, TCc, gas flow, swelling properties). – Experiments to characterize the geotechnical properties of compacted claystone-bentonite-mixtures as sealing material (water

retention curves, water re-saturation, water permeability and gas migration, swelling capacities). – Accompanied by numerical modelling activities. – Deliverable D3.32

⇒ POSTER Session

GRS activities within DOPAS/ELSA

Simplified illustration of the whole dam structure

Definition of the three devices of a sealing element and

identification of the boreholes

Drift sealing element Depth 945 m Finished in 1992 Investigated in 2003 Salt concrete (72% crushed salt, 18%

cement, 10% NaCl-brine) 8 m in length, 5.5 m in width, 3.4 m in height

Structure of salt concrete

B4

B5

EDZ Host rock

Contact zone

Boreholes Borehole in the contact zone GRS specimens

Available material from existing dam in rock salt

Rock salt from the Excavation

Damaged Zone (EDZ)

Available material for lab tests (in situ / lab)

Sorel concrete crushed salt, magnesium

oxide, MgCl2-brine

Salt concrete crushed salt, blast-furnace

cement, NaCl-brine

Crushed claystone/ bentonite mixtures with grains d < 10 mm

Deformation and damage behaviour of salt concrete

Stress-strain-permeability behaviour of salt concrete samples

Deformation and damage behaviour of salt concrete

Permeability as a function of volumetric strain. Laboratory data for confining pressures of 1-3 MPa

are compared with calculated permeabilities.

Permeability evolution of sorel concrete (corrosion processes)

Advection experiments with sorel concrete • Investigation of development of permeability of

sorel concrete (MgO-based concrete) in contact with NaCl and MgCl2-based solutions.

Functional principle • Concrete is placed in advection cell, cast in araldite • Inflow: Solution pressure 20 bar. • Outflow: Solution is collected and permeability

calculated. Experimental set-up

Advection experiments with sorel concrete • Investigation of development of permeability of

sorel concrete (MgO-based concrete) in contact with NaCl and MgCl2-based solutions.

Functional principle • Concrete is placed in advection cell, cast in araldite • Inflow: Solution pressure 20 bar. • Outflow: Solution is collected and permeability

calculated.

Results Sorel concrete / NaCl-based solution • Permeability measureable after 7 to 60 days. • Clear increase of permeability in all samples up to

a level of 10-17 m2/s. • Assumption: no further increase of permeability

because solution passes sample faster than it needs for corrosion if a value around 10-17 m2/s is reached.

Permeability evolution of sorel concrete (corrosion processes)

Sealing in integrated PA: Closer to reality Copy from A. Rübel (Session 2)

Sealing material is disturbed → permeability is increasing Original sealing material

Excavation disturbed Zone (EDZ) around sealing with increased permeability

Behaviour of salt concrete sealing material Copy from A. Rübel (Session 2)

Time [a]

Res

ista

nce

[Pa·

a/m

³]

100 101 102 103 104106

107

108

109

1010

SealingEDZConcrete core

O:\projekte\pass\entwuerfe\modell\140212_example_r.lay

Integrated PA

Hydraulic sealing capacity of combined samples

Hollow salt cylinder, salt concrete core and salt slurry

Complete combined sample

kgas (concrete) < 1.E-18 m²

kgas(EDZ) < 1.E-22 m²

kgas (interface) = f(t)

Pilot test

Isostatic cell arrangement and coated sample before installation

Pilot sample after jacket failure and dismantling, center part after cutting

Combined system

Phase 1: Compaction of the sample – confining pressure 5 and 10 MPa, sample stays in contact with NaCl-based solution ⇒ Permeability to NaCl-based solution is around 10-18 m2/s.

kBrine = const.

kBrine = f(time)

Combined system Phase 1: Re-compaction processes (HM)

time [ h ]

Combined system Phase 2/3: Corrosion processes (CH)

Phase 2: Permeability increases immediately in contact with MgCl2-based solution, probably as result of higher injection pressure. Afterwards, permeability decreases because Brucit (Mg(OH)2) is built and plugs the pores. Additionally, pH decreases to 8-9. Phase 3: The smaller pH-value results in decomposition of portlandite (Ca(OH)2) and CSH-phases (Calcium-silicate-hydrates). ⇒ Permeability increases.

time [ h ]

Coupled behaviour of shaft sealing materials • GRS is investigating combined systems of salt concrete seal elements and surrounding rock

salt at the laboratory scale in order to get the temporal evolution of the overall permeability. Currently, the following results have been obtained: • At dry conditions and at a moderate confining stress up to 5 MPa, reconsolidation is slow. A

potentially existing highly permeable contact seam between the seal element and the rock will not be closed, at least not in the short term.

• With an intact seal element, a confining stress of 5 MPa is, however, sufficient to prevent brine flow along the seal. In the presence of brine, contact seam and EDZ are quickly closed, resulting in overall permeability below 10-20 m2.

• A pre-damaged seal element (e.g., damaged by shrinkage fracturing during construction) will not be reconsolidated at a confining stress of 5 MPa, even if brine is present.

• At a stress level of 10 MPa reconsolidation of the pre-damaged seal element is effective and permeability decreases.

• Chemical alteration processes could be observed when a corrosive brine is used. The next steps in the experimental investigations will be: • to dismantle the re-consolidated sample and use microscopic methods to investigate pathway

reduction and • to perform further experiments to investigate variability of results and derive generally valid

material behaviour. Available physical models of rock salt and salt concrete have been applied already but simulation/ improvement cycles should be performed to advance model qualification.

Conclusions and further R&D work

Acknowledgements

J. Dittrich U. Hertes

T. Hörbrand K. Jantschik H. C. Moog

J. Müller K. Wieczorek C.-L. Zhang

Questions ...

The research leading to these results has received funding from the European Atomic Energy Community's (Euratom) Seventh Framework Programme FP7/2007-2013, under Grant Agreement No. 323273 for the DOPAS project and the Federal Ministry for Economics and Energy (BMWi), represented by the Project Management Agency Karlsruhe (PTKA-WTE), contract no. 02E11122 / 02E11132 / 02E10377.