Impact of geochemical evolution of cementitious engineered barriers on sorption behaviour

1. 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

2. 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

3. Context • LLIW-SL waste: near-surface disposal Environmental effects • Physical • Mechanical • Chemical Figuur inplanting Degradation of concrete

4. Context Main chemical degradation process: leaching / decalcification: • Dissolution of cementphases • 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

5. Rain water Soil reactions Concrete reactions Clay reactions soil soil 14 Soil water 12 H p 10 8 clay clay Time Clay water Clay water Drainage water Chemical degradation due to disequilibrium with surroundings of engineered barrier Cat A: influence of atmospheric conditions and cover layers

6. 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

7. Comparison of Cat A and Cat B/C

8. Simulation of chemical degradation of concreteFirst requirement: Cement database • Clinkers + water => 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 0-50°C

9. Simulation of chemical degradation of concreteCement database: Benchmarking Carbonation Decalcification Leaching of 100 g hydrated OPC with Boom Clay pore water at 16°C Verification in CaO-SiO2-H2O system, 100 g OPC, w/c 0.58

10. Simulation of chemical degradation of concreteCase study for leaching with soil water

11. Simulation of chemical degradation of concreteCase study for leaching with soil water

12. 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)

13. Simulation of chemical degradation of concrete : Cat B/CThe lifetime of cementitious supercontainer: > 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

14. 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)

15. Sorption values of RN as function of concrete degration stateCat A approach • Compilation of literature data of Kd values for critical RN (SCK•CEN) • Description of adsorption processes and influencing factors (SCK•CEN) • 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

16. Sorption values of RN as function of concrete degration stateCat A approach • Consistent dataset with Kdvalues 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

17. Sorption values of RN as function of concrete degration stateExample Cs and I Iodide Cesium

18. Sorption values of RN as function of concrete degration stateExample U

19. COUPLING TIME-DEPENDENT SORPTION VALUES OF CONCRETE DEGRADATION WITH A RADIONUCLIDE MIGRATION MODEL

20. ConclusionsApplicability for B&C 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 -> 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

21. ConclusionsApplicability for B&C waste • Sorption values • Available for some RN present in B&C 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