German contribution: CH/HM coupled behaviour of shaft sealing materials
1. German contribution:
CH/HM coupled behaviour of shaft sealing materials
Oliver Czaikowski, Kyra Jantschik, Helge C. Moog, Klaus Wieczorek & Chun-Liang Zhang
GRS , Germany
DOPAS: Full-scale
demonstration of the
feasibility and
performance of plugs
and seals
2. • Five experiment being designed,
implemented and assessed across
seven work packages
• Supported by materials development
• Three experiments in crystalline
rocks:
• DOMPLU (Äspö)
• POPLU (ONKALO)
• EPSP (Josef)
• One experiment related to clay:
• FSS (St Dizier)
• A set of experiments and
performance assessment studies
related to salt:
• ELSA (generic German concept)
The DOPAS Project
3. Experiments in crystalline and clay rock
DOMPLU (SKB) and POPLU
(POSIVA):
• confine the backfill in the tunnel,
support backfill saturation and to
provide a barrier against water
flow / bentonite erosion
• Main components: concrete
plug and watertight seal
EPSP (SURAO/CTU):
• Composite structure of concrete domes and bentonite
pellets
FSS (ANDRA):
• Limit water flow and reduce
groundwater velocity
• Swelling clay core and low-
pH concrete containment
4. German 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
5. • 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
Issues addressed by GRS within DOPAS
6. 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
Drift sealing element
Depth 945 m, finished in 1992
Salt concrete
(72% crushed salt, 18% cement, 10% NaCl-brine)
8 m in length, 5.5 m in width, 3.4 m in height
7. Deformation and damage behaviour of salt concrete
Stress-strain-permeability behaviour of salt concrete samples
8. 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)
9. Sealing in integrated PA: Closer to reality
Sealing material is disturbed
→ permeability is increasing
Original sealing material
Excavation disturbed Zone (EDZ) around sealing with
increased permeability
10. 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(Salt) < 1.E-22 m²
kgas (interface) = f(t)
11. 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 ]
12. 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 ]
13. Coupled behaviour of sealing materials in contact with surrounding rock
• 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 can be observed when a corrosive brine is present.
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
14. Acknowledgements
J. Dittrich
U. Hertes
T. Hörbrand
J. Müller
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.
