Salt Reconsolidation

1. 8th US/German Workshop on Salt Repository
Research, Design, and Operation
K. Wieczorek, F. Hansen, N. Müller-Hoeppe
Middelburg, The Netherlands
September 5-7, 2017

2. Breakout Session:
Reconsolidation of salt backfill material
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 Role of crushed salt backfill in a nuclear waste repository
 decay heat transfer to the host rock
 stabilization of excavations
 after reconsolidation:
Long-term barrier against brine
 Key question: How and when will sufficiently low
porosities/permeabilities be reached?
 Systematic reduction of uncertainties is
 necessary for reliable repository dimensioning
 highly desirable for further optimization

3. Open issues – process understanding
 Relevant mechanisms of salt reconsolidation
 Dislocation creep
 Pressure solution creep
 Grain boundary diffusion
 Grain displacement and breakage
 Which processes are most relevant
at which conditions?
 Porosity range
 Temperature
 Dry or moist conditions
 Saturation state  pore pressure effects
 Effect on hydraulic behavior?
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modified after Spiers et al. 1990

4. Open issues – experimental data
 A large database exists, but – due to
revised safety requirements – it is
incomplete
 What is needed
 Fill the gaps – low porosity range with
relevant load conditions
 High accuracy, especially in (low) porosity
determination
 Bridge gap between phenomenological
response and underlying processes
 Tune experiments to needs for model
validation
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PermeabilitytoBrine[m²]
Porosity [%]
90 C, A9/3b
90 C, A9/4b
130 C, A9/2b
130 C, A9/4
130 C, A9/5a
90 C, A9/5b Q-brine
40 C, A9/f16a
40 C, A9/f16
Gas measurement [FRÖ 99]
Own gas measurement
Wet crushed salt [GRS 148]

5. Open issues – models
 A number of models describing crushed
salt reconsolidation is existing
 Validation/calibration is incomplete
 Models need to be investigated in detail
 Which processes are/can be simulated at all?
 In which range (of load conditions, porosity,…)
is the models’ application admissible?
 Which are the parameters determining the
output?
 Benchmark with cycles of calculation-
assessment-adjustment/improvement
needed
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Porosity evolution in center of a drift, brine inflow after 100 years (REPOPERM 2)
Porosity evolution predictions (VSG)

6. Ideas for a project (compiled by GRS,
BGR, DBE TEC, IfG, TUC, SNL)
 A project aimed at clearing the deficits in prediction capability
should include all three issues and their interrelation
 Modelling
 Experimental investigations
 Process understanding
 Complementary idea: Tune backfill material to attain high
performance characteristics early in a salt repository lifetime
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