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Interactions between cementitious engineered barriers and Boom Clay: the alkaline plume effects

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Literature review best available knowledge ... by forming zeolites, CSH, and calcite; decrease migration by porosity clogging ... – PowerPoint PPT presentation

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Title: Interactions between cementitious engineered barriers and Boom Clay: the alkaline plume effects


1
Interactions between cementitious engineered
barriers and Boom Clay the alkaline plume effects
  • Lian Wang and D. Jacques
  • P. De Cannière, H. Moors, M. Van Gompel, M.
    Aertsens, and M. Honty

Euridice exchange meeting
January 29, 2009, Mol, Belgium
2
Alkaline plume in clay
Cementitious supercontainer as the backfill, thus
55,000 tons concrete will be inserted in Boom
Clay
3
Contents
  • Objectives and methodology
  • Literature review best available knowledge
  • Experimental evidences of alkaline plume effects
    in Boom Clay
  • Detailed geochemical coupled modelling
  • Conclusions and future works

4
Reports concerning alkaline plume perturbation to
Boom Clay
Wang, L., Jacques, D. and De Cannière, P. (2007)
Effects of an alkaline plume on the Boom Clay as
a potential host formation for geological
disposal of radioactive waste, SCK CEN-ER-28,
first full draft. Wang, L. (2006) Near-field
chemistry of a HLW/SF repository in Boom Clay
Scoping calculations relevant to the
supercontainer design, SCK CEN-ER-17, first full
draft. Wang, L., De Cannière, P., Jacques, D.,
Moors, H., Van Gompel, M., and Aertsens, M.
(2004) Experimental and modeling studies of Boom
Clay exposed to an alkaline perturbation, SCK
CEN-R-4019, Mol, Belgium. Savage, D. (1999)
Alteration of Boom Clay by hyperalkaline fluids
a review of potential processes and input data
for reaction-diffusion simulations,
ONDRAF-6185A-GEN-I, QuantiSci, February, 1999,
UK. Lynch, P. and Savage, D. (2000) Alteration of
Boom Clay by hyperalkaline fluids mathematical
modeling of the reference cases, Report to
NIRAS/ONDRAF, ONDR-6185A-GEN-2. Lynch, P. (2001)
Alteration of Boom Clay by hyperalkaline fluids
mathematical modeling of the experiment, Report
to NIRAS/Ondraf, ONDR-6185A-GEN-3, June 2001.
5
Objectives and methodology
  • Objectives
  • To assess the nature and the extent of effects of
    an alkaline plume on Boom Clay properties
  • Methodology
  • Literature review best available knowledge
  • In-house experiment
  • Detailed modeling and mass balance constraints

6
Literature review best available knowledge
  • Previous studies Switzerland (OPA), France
    (COX), bentonite-cement, ECOCLAY, Natural
    analogue
  • Mineral alteration ion exchange dissolution
    clays, quartz, feldspars, and organic matter
    precipitation zeolites, CSH, and calcite
  • Kinetics not important gt 1 000 a
  • Porosity likely to decrease
  • RN retention zeolites and CSH are strong sorbing
    minerals
  • Colloids not important because of low
    concentration
  • Numerical modeling useful tool to rationalize
    arguments to support the safety analysis
  • Extent of an alkaline perturbation few meters

7
In-house experiments
  • Chemical analysis of the percolate
  • Mineralogical and radio analysis of the core

?38?32 mm
YCW and ECW
8
Experimental evidences effects on pH
pH front advances faster in YCW than ECW
YCW Na/K, pH 13.2
ECW Ca(OH)2 solution, pH 12.5
9
Experimental evidences clay alterations
K/Ca retention by clay in ECW
Na/Si/Al dissolving from clay in YCW
5 a
10 a
7 a
10
Experimental evidences diffusion
  • H14CO3- is retarded in ECW
  • precipitation of calcite
  • isotopic exchange unlikely

Volume percolated ml
  • the retardation can be explained by
  • a decreased apparent diffusion

11
Experimental evidences RN retention
  • Sr eluting by YCW probably due to Sr-Na/K ion
    exchange
  • Sr retained by ECW likely because of Sr
    co-precipitation with neo-calcite

12
Experimental evidences dissolution of NOM by YCW
  • high pH elute NOM
  • only part of NOM is alkali extractable

3 a
13
Experimental evidences hydraulic conductivity
Hyd. Con. Increased in YCW - diss. Clay OM
Hyd. Con. decreased in ECW - Precipitation calcite
5 a
5 a
14
Detailed geochemical coupled modelling
  • Boom Clay
  • Equilibrium precipitation/dissolution of Boom
    Clay minerals
  • Interactions with solid phase
  • Ion exchange on fixed CEC-complex (clay)
  • Ion exchange on pH-dependent CEC complex (organic
    matter)
  • Proton surface complexation on illite/montmorillon
    ite
  • Equilibrium precipitation/dissolution for
    secondary minerals
  • Cement model
  • Simplified concrete model portlandite,
    afwillite, hydrogarnet, hydrotalcite, Na2O, K2O

15
Model approach
  • Radial diffusion
  • No feed-back from chemistry on porosity and D

16
Base model first 25 000 y
Concrete
Boom Clay
17
Base model 105 years
Concrete
Boom Clay
18
Base model mineralogy in concrete
19
Sensitivity to model formulationpH (25 000 y)
20
Mass balance constraints
a Clays b OH- c AlO2- d HSiO3- e Mg2
V volume BC disturbed L the thickness of BC
disturbed n moles of clay minerals dissolved by
cement D density of BC wt percentage of clay
minerals in BC
The thickness of BC disturbed by cement 1 to 3
meters
21
Conclusions and future work
  • Conclusions
  • The thickness of the Boom Clay perturbed
  • 1 to 3 meters by model and mass balance
    calculations
  • Effects on diffusion
  • No negative impacts observed
  • Effects on RN retention
  • Positive effects increase sorption by forming
    zeolites, CSH, and calcite decrease migration by
    porosity clogging
  • Possible negative effects dissolution clays/NOM
    by YCW and release alkaline earth elements like
    Sr (observed in accelerated percolation
    experiments within the perturbed zone)
  • Future work
  • Updating modeling with improved cement and clay
    models and a consistent database (unlikely to
    affect the results to big extent)
  • Ongoing experiments
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