Outcome of the Repoperm Project

1. Outcome of the Repoperm Project
Klaus-Peter Kröhn, GRS
6. September 2017
8th US/German Workshop on Salt Repository Research,
Design, and Operation
September 5-7th, Middelburg, Netherlands

2. Overview
Scope
Selected workpackages
Conclusions, open questions, and recommendations
2

3. 3
Scope

4. Project REPOPERM
Scope 4
Joint project of
Mechanical and hydraulic behaviour
of compacting crushed salt backfill
at low porosities
REPOPERM project - phase 1
 October 2007 until March 2009
REPOPERM project - phase 2
 May 2010 until July 2016

5. Key question for Phase 1
 Threshold porosity F0 → permeability k0 = 0 m² ?
Main result of Phase 1
 A possible F0 lies in a range where measurement of porosity is of inherent high uncertainty
Key question for Phase 2
 Relevance of F0
→ reliable prediction of crushed salt behaviour under repository conditions
 Mechanical and hydraulic data for compaction especially of wet material
Scope 5
Objectives

6. REPOPERM project - phase 1
Scope 6
Tasks
 Data review
 Compaction test
Results
 Criteria for in-situ relevant laboratory test conditions
 Porosity-permeability relation for gas and brine
 High inherent uncertainties in determination of a porosity < 1-2%
 No reliable constitutive equations for two-phase flow
Porosität [-]
Permeabilität[m²]
10
-3
10
-2
10
-1
10
-24
10-22
10
-20
10-18
10
-16
10-14
d<32mm; Spindelöl
d<32mm; Spindelöl
d<16mm; Lauge
d<16mm; Lauge
d<16mm; Spindelöl
d<16mm; Spindelöl
d< 8mm; Spindelöl; BGR D-A-003
d< 8mm; Spindelöl; BGR D-A-010
d< 4mm; Spindelöl; BGR D-A-004
d< 4mm; Spindelöl; BGR D-A-011
d< 2mm; Spindelöl; BGR D-A-005
d< 2mm; Spindelöl; BGR D-A-012
d< 8mm; Stickstoff; G.3S-2
d< 8mm; Stickstoff; GRS Debora
Extrapolation der Bandbreiten
aus Abb. 2.16
Ungestörtes Steinsalz
Phase 1
porosity [-]
permeability[m²]
0.02 0.04 0.06 0.08 0.1 0.12
10
-23
10-21
10
-19
10-17
10
-15
10-13
brine
spindle oil
nitrogen
present test; nitrogen
present test; brine
present test; brine
D-A-025
bandwidths fit by eye
gas permeability
brine permeability
Phase 2

7. REPOPERM project - phase 2
Scope 7
Experimental investigations
 Examining the porosity in relevant, past experiments
 Influence of the sieve line on compaction behaviour
 Triaxial compaction test with dry material at low porosities
 Influence of humidity on compaction
 Permeability associated with low porosity
 Constitutive relations for two-phase flow
 Microstructural Investigations
Basics for numerical modelling of compacting crushed salt
 Phenomenology and physics related to crushed salt compaction
 Development/definition and comparison of material models
 Benchmark calculations and parameter improvement
 Scaling-rules for capillary pressure
 Application of Discrete Element Codes
THM-coupled model calculations
 Relevant scenarios and boundary conditions
 Inflow into the drift backfill at the drift seal

8. REPOPERM project - phase 2
Scope 8
Experimental investigations
 Examining the porosity in relevant, past experiments
 Influence of the sieve line on compaction behaviour
 Triaxial compaction test with dry material at low porosities
 Influence of humidity on compaction
 Permeability associated with low porosity
 Constitutive relations for two-phase flow
 Microstructural Investigations
Basics for numerical modelling of compacting crushed salt
 Phenomenology and physics related to crushed salt compaction
 Development/definition and comparison of material models
 Benchmark calculations and parameter improvement
 Scaling-rules for capillary pressure
 Application of Discrete Element Codes
THM-coupled model calculations
 Relevant scenarios and boundary conditions
 Inflow into the drift backfill at the drift seal

9. 9
Selected workpackages

10. time [d]
porosity[-]
0 500 1000 1500
0
0.05
0.1
0.15
0.2
0.25
0.3 bounding porosity for sample 1
bounding porosity for sample 2
bounding porosity for sample 3
flooding of
sample 1
flooding of
sample 2
time [d]
porosity[-]
stress[MPa],temperature[°C]
0 500 1000 1500
0
0.05
0.1
0.15
0.2
0.25
0.3
0
20
40
60
80
100
initial porosity
terminal
porosity
flooding
Long-term multi-step load-controlled compaction test
Uniaxial test running for 1654 days
Sample data
Load
 Increasing mechanical load (up to 18 MPa)
 Varying temperature (up to 90 °C)
 Flooding with brine
Selected workpackages 10
Sample Initial moisture content Terminal porosity
1 0.0 % 1.11 %
2 0.1 % 0.88 %
3 1.0 % 2.00 %

11. Test on constitutive relations for two-phase flow
Compacting crushed salt;
Gas flow test
Sample selection
→ single-phase gas permeability
Installation of samples
Saturating with brine
→ single-phase brine permeability
Applying gas pressure;
observing outflow;
stepwise pressure increase
→ air entry pressure
Measuring brine & gas outflow;
increasing gas pressure stepwise
→ capillary pressure
→ effective gas permeability
→ gas saturation
crushed
salt
gas
porosity [%]
gaspermeability[m²]
7 8 9
10-15
10-14
10-13
crushed
salt
load
brine
gas
gas
Selected workpackages 11

12. Sample data
Selected workpackages 12
Constitutive relations for two-phase flow
Sample Porosity [%] Gas permeability [m²] Brine permeability [m²]
P1 7.33 7.5·10-15 7.5·10-15
P2a 8.13 1.7·10-14 2.0·10-15 - 2.0·10-14
P2b 7.43 1.3·10-14 2.0·10-15 - 1.1·10-14
M1a 10.70 1.0·10-13 1.3·10-13
M1b 7.69 1.2·10-14 1.0·10-14
M2a 6.10 2.0∙10-15 1.4∙10-15
M2b 5.20 1.1∙10-15 2.5∙10-17
saturation [-]
capillarypressure[MPa]
0 0.2 0.4 0.6 0.8 1
10
-2
10-1
100
sample P
sample P; disturbed conditions
sample M1a
sample M1a; unreliable
sample M1a; spoiled
sample M1b
sample M1b; spoiled
sample M2b
Brooks-Corey functions
saturation [-]
relativegaspermeability[-]
0 0.2 0.4 0.6 0.8 1
0
0.02
0.04
0.06
0.08
sample P
sample P; disturbed conditions
sample M1a
sample M1a; unreliable
sample M1a; spoiled
sample M1b
sample M1b; spoiled
sample M2b
Brooks-Corey function (P)
Brooks-Corey function (M1a)
Brooks-Corey function (M1b)
Brooks-Corey function (M2b)

13. Applicability of modelling tools
First calibration of parameters for FADT
First generic THM-model for salt backfill
 compaction of crushed salt in a drift
 thermal gradient
 brine inflow at a certain point in time
 CODE_BRIGHT with repository-relevant material parameters
→plausible and coherent results
Validity of material models
 Three different tests (BAMBUS, BGR-test, REPOPERM)
 Calibration leads to three different parameter sets
 None of the sets could successfully be applied to one of the other two tests
 Same result with interpolated parameters
Three approaches were compared in detail (Hein, Heemann, Olivella)
 Qualitatively similar behaviour
 Agreement doubtful especially in case of low porosities
Some constitutive equations are not valid over the whole range of primary
variables (stress, temperature, porosity, …)
Selected workpackages 13

14. Specific topics
Mechanics
 Uncertainty in the grain density → uncertainty of void ratio: Δe ≈ 0.0045 – 0.0065
 The fractions of the smaller grain sizes dominate the compaction behaviour
 Results of triaxial and uniaxial compaction tests increasingly disagree towards low porosities
Hydromechanics
 Uniaxial and triaxial tests indicate a transition from dry to wet compaction
between 0.3% and 0.6% moisture content
 No significant influence of high relative humidity in the pore air on compaction
Hydraulics
 Very little adsorption of water on crushed salt in a humid atmosphere
 Confirming the porosity-permeability relation from Phase 1
 Two-phase/unsaturated flow
• Measurement of two-phase flow properties of crushed salt with a repository-relevant grain
size distribution down to a gas permeability of 10-15 m² is possible
• Application of the theory of Brooks and Corey
 works for the capillary pressure
 fails for relative permeability
Selected workpackages 14

15. 15
Conclusions,
open questions, and
recommendations

16. Conclusions
Considerable advance in knowledge and understanding
First experimental data → parameters for wet compaction (FADT)
First repository relevant THM-model for salt buffer
A row of specific questions answered
Limits of presently used models
Hydro-mechanical behaviour of compacting crushed salt is not yet
 completely characterized (e.g. validity of constitutive equations)
 sufficiently understood (e.g. permeability under unsaturated conditons)
Water vapour will spread out through the backfill unimpeded
Material parameters are presently test dependent
Conclusions, open questions, and recommendations 16

17. Open questions
(Hydro-)Mechanical properties
 Effekt of flooding at high porosities on compaction
 Effect of entrapped air on expulsion of brine during compaction
Reason for disagreement of tri- and uniaxial tests
Dynamics of transition from dry to wet compaction
Impact of deviations in the grain size distribution
 Compaction of material exclusively with large grains
 Dependence of constitutive equations for two-phase flow on porosity
Relevance of threshold porosity
Conclusions, open questions, and recommendations 17

18. Enhance the predictive capability of the numerical models
 Catalogue
• all constitutive equations
• all supporting experimental evidence
• range of validity
• uncertainties
 Ensure validity constitutive equations of over the whole range of possible THM conditions
• do supplemental experiments where necessary
Material parameters must not be allowed to be test dependent!
 Increase understanding of the tests
 e.g. reconcile results of uniaxial and triaxial tests
 Include additional effects and processes like wall friction and hardening
Investigate
 Relevance of threshold porosity with a well-founded numerical model
 Impact of deviations in the grain size distribution
 Transition between dry and wet compaction
 Impact of vapour transport on canister corrosion
Decide about two-phase flow parameters
 further measurements
 dependency on grain size distribution
 alternatives
Conclusions, open questions, and recommendations 18
Recommendations

19. Thank you for listening
Thank you for sponsoring:
Thanks to all the contributing collegues
Christian Lerch (DBE TEC)
Rüdiger Miehe (GRS)
Dieter Stührenberg (BGR)
Michael Jobmann (DBE TEC)
Ulrich Heemann (BGR)
Oliver Czaikowski (GRS)
Christian Müller (DBE TEC)
Chun-Liang Zhang (GRS)
Helge Moog (GRS)
Sonja Schirmer (DBE TEC)
Larissa Friedenberg (GRS)
Liselotte von Borstel (DBE TEC)
Jens Wolf (GRS)
Jürgen Dittrich (GRS)
Karsten Hellwald (GRS)
Jürgen Müller (GRS)
All the technicians not mentioned here