Impact of geochemical evolution of cementitious engineered barriers on sorption behaviour

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Impact of geochemical evolution of cementitious
engineered barriers on sorption behaviour

• D. Jacques, L. Wang, E. Martens, P. De Cannière,
  J. Berry, J. Perko, D. Mallants
• SERCO

Euridice Exchange Meeting
January 29, 2009 Mol, Belgium
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Content

• Context (Cat A)
• Chemical degradation due to disequilibrium with
  surroundings
• Simulation of chemical degradation of concrete
• Sorption values of RN as function of concrete
  degration state
• Coupling time-dependent sorption values to
  degradation state
• Conclusions

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Context

• LLIW-SL waste near-surface disposal

Environmental effects

• Physical
• Mechanical
• Chemical

Figuur inplanting
Degradation of concrete
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Context
Main chemical degradation process leaching /
decalcification

• Dissolution of cement phases
• Gradual decrease in pH
• Change in aqueous and solid phase composition
• Four chemical degradation states

• Change in sorption of RN
• ?
• Time space relations of degradation states
  in engineered barriers

time
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Chemical degradation due to disequilibrium with
surroundings of engineered barrier
Cat A influence of atmospheric conditions and
cover layers
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Chemical degradation due to disequilibrium with
surroundings of engineered barrier
Cat B/C influence of Boom Clay
Diffusion of Boom Clay water in concrete
Diffusion of concrete water in Boom Clay
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Comparison of Cat A and Cat B/C
Cat A Cat B/C
Dimensionality Transport mechanism Interaction surroundings Degradation mechanism Boundary condition Safety function Processes 1D Advection One-direction Dissolution Decalcification C-S-H Leaching Uncertain Main function Sorption(concen-tration RN low) 3D Diffusion Interactive Dissolution Decalcification C-S-H Carbonation Well defined Nice to have Solubility limited
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Simulation of chemical degradation of
concreteFirst requirement Cement database

• Clinkers water gt cement with typical cement
  phases (cfr. Wang and Jacques)
• Portlandite
• C-S-H (calcium silicate hydrates)
• AFm (CASH)
• AFt (ettringite CsAH)
• State-of-the-art temperature dependent model
• Originally format only for GEMS-model
• Converted PSI-database into PHREEQC-format for
  temperature range 0-50C

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Simulation of chemical degradation of
concreteCement database Benchmarking
Carbonation
Decalcification
Leaching of 100 g hydrated OPC with Boom Clay
pore water at 16C
Verification in CaO-SiO2-H2O system, 100 g OPC,
w/c 0.58
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Simulation of chemical degradation of
concreteCase study for leaching with soil water
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Simulation of chemical degradation of
concreteCase study for leaching with soil water
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Simulation of chemical degradation of
concreteTransport in concrete structures
Based on very simplifying assumptions

• State I concrete degradation rate of 3.2 m per
  year
• State II 0.0029 m per year (345 years for 1
  meter)
• State III 2.75 x 10-4 m per year (3640 years for
  1 meter)

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Simulation of chemical degradation of concrete
Cat B/CThe lifetime of cementitious
supercontainer gt 80,000 a

• porosity change considered
• self-sealing by carbonation
• the time self-sealing occurs depends on gridding
• in reality, total clogging unlikely

• diffusion of NaHCO3 water into NF
• equilibrium without kinetics
• no porosity change

pH
Time, a
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Simulation of chemical degradation of
concreteRelevance for B/C

• Cement database
• Modelling of degradation states and pH evolution
  in concrete with equilibrium model
• Cfr. presentation Wang et al. on alkaline plume
• Composition of Boom Clay water is beter
  characterized, but difficulties in defining the
  effects of concrete water on Boom Clay (buffer
  capacity, secondary minerals, cfr. presentation
  Wang et al. on alkaline plume)

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Sorption values of RN as function of concrete
degration stateCat A approach

• Compilation of literature data of Kd values for
  critical RN (SCKCEN)
• Description of adsorption processes and
  influencing factors (SCKCEN)
• International Expert Panel (ANDRA, CEA, NAGRA,
  NDA, PSI, ...)
• Critical review of values
• Provide estimates of Kd for each degradation
  state best estimate, minimum and maximum value
• Provide scientific reasoning for selection of the
  values

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Sorption values of RN as function of concrete
degration stateCat A approach

• Consistent dataset with Kd values for critical
  RN
• Tracebility
• Database of all reviewed papers
• Detailed summary report includingscientific
  reasoning for selection of values (Wang et al.)
• Detailed minutes of meeting with all discussions

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Sorption values of RN as function of concrete
degration stateExample Cs and I
Iodide
Cesium
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Sorption values of RN as function of concrete
degration stateExample U
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COUPLING TIME-DEPENDENT SORPTION VALUES OF
CONCRETE DEGRADATION WITH A RADIONUCLIDE
MIGRATION MODEL
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ConclusionsApplicability for BC waste

• Thermodynamic database
• State-of-the-art cement database
• Temperature-dependent thermodynamic constants for
  both cement phases and aqueous species
• Modelling degradation states
• Coupling (advective)-diffusive transport with
  geochemical equilibrium modelling
• In PHREEQC-format -gt applicable for complex 3D
  radial configurations when diffusion is the only
  (main) transport mechanism
• Information on pH with time important for
  retention and solubility of RN

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ConclusionsApplicability for BC waste

• Sorption values
• Available for some RN present in BC waste
• Redox sensitive RN information was provided for
  both oxidizing as reducing conditions (if
  information is available)
• Announcement
• Course on reactive transport modelling with HP1
  (HYDRUS-1D and PHREEQC)
• Gent, September 28 Oktober 2 2009
• information Monique van Geel