Numerical Simulations of Atmospheric Carbonation in Concrete Components of a Deep Geological Intermediate Low Level Waste Disposal NUCPERF 2012 P. Thouvenot 1, O. Bildstein 1, S. Poyet 2, I. Munier 3, B. Cochepin 3, X. Bourbon 3, E. Treille 3 1 CEA (French Alternative Energies and Atomic Energy Commission), LMTE, Cadarache 2 CEA (French Alternative Energies and Atomic Energy Commission), LECBA, Saclay 3 ANDRA (French Radioactive Waste Management Agency)

FRENCH CONCEPT : RADWASTE REPOSITORY IN A CLAYSTONE FORMATION AT 500 M DEPTH Current design of deep underground repository for high and intermediate level long-lived waste

FRENCH CONCEPT : RADWASTE REPOSITORY IN A CLAYSTONE FORMATION AT 500 M DEPTH Atmospheric carbonation of overpack during the operating period Bitumized waste Cemented waste Compacted metallic waste Organic waste

CARBONATION ISSUES FOR RADWASTE REPOSITORY Overpack carbonation pH decrease Corrosion increase Overpack cracking What about reversibility ? Ventilation (100 years)

DRYING AND CARBONATION PROCESSES IN ILLW OVERPACK

PHENOMENOLOGY: CAPILLARY FLOW Flow law (generalized Darcy law): Lowering of the dew point due to capillary effects (Kelvin equation in EOS 4): Water relative permeability (Van Genuchten): Gas relative permeability (Corey): Klinkenberg effect (gas flow at low pressure):

PHENOMENOLOGY: DIFFUSION Air and water gases diffusion: CO 2 and other gases: Aqueous diffusion: Effective diffusion : Tortuosity (Millington-Quirk):

PHENOMENOLOGY: DIFFUSION Air and water gases diffusion: CO 2 and other gases: Aqueous diffusion: Effective diffusion : Tortuosity (Millington-Quirk): 1st MAJOR COUPLING EFFECT!! Sliq D i,g

DRYING PHENOMENON : PARAMETERS VALUES 3 different concrete materials: High Performance Concrete (HPC) Intermediate Performance Concrete (IPC) Low Performance Concrete (LPC) HPCIPCLPC Porosity Intrinsic permeability to liquid (m²)1e-211e-191e-17 Intrinsic permeability to gas (m²)1e-191e-171e-15 Relative permeability m – Slr – Sls – Sgr0.481 – 0.0 – 1.0 – – 0.0 – 1.0 – – 0.0 – 1.0 – 0.0 Capillarity pressure m – P 0 (MPa) – Pmax (MPa)0.481 – – – Molecular diffusion coefficient gaseous phase (m²/s) water2.4e-05 Molecular diffusion coefficient gaseous phase (m²/s) CO 2 1.6e-05 Molecular diffusion coefficient in aqueous phase (m²/s)1.9e-09 Millington-Quirk a parameter2 Millington-Quirk b parameter4.2 Klinkenberg parameter (MPa)0.45

SIMULATIONS CONFIGURATION 1D half section package container (section = 11 cm) Carbonation on both sides Ventilation air at 25°C and 40% relative humidity Initial liquid water saturation assumed to be cm 25°C 40%RH 25°C 40%RH

DRYING RESULTS TR EOS9 (Richards) and TR EOS4 (full multiphase) comparison Drying process slows down when transport characteristics of concrete are enhanced. Drying with Richards’ equation (EOS9 without gaseous diffusion) is slightly slower than with full multiphase model (EOS4).

NUMERICAL RESOURCES FOR CARBONATION SIMULATIONS Carbonation during the operation period TOUGHREACT EOS 4 Few numerical developments CEA/ANDRA Thermodynamic database Thermoddem 1v12 Simulations performed with Intermediate Performance Concrete for aqueous species and mineral phases full multiphase flow

CHEMICAL PARAMETERS Primary phases Secondary phases Kinetics of dissolution / precipitation Phase Volume % Calcite72.12 Portlandite5.73 CSH Monocarboaluminate2.26 Ettringite3.60 Hydrotalcite0.39 Hydrogarnet-Fe (C3FH6)2.05 Phase typePhases OxidesMagnetite, Amorphous silica HydroxidesBrucite, Gibbsite, Fe(OH) 3 Sheet silicatesSepiolite Other silicatesCSH 1.2, CSH 0.8, Straetlingite, Katoite_Si Sulfates, chlorides, other saltsGypsum, Anhydrite, Burkeite, Syngenite, Glaserite, Arcanite, Glauberite, Polyhalite CarbonatesCalcite, Nahcolite OtherHydrotalcite-CO 3, Ettringite, Dawsonite

CHEMICAL PARAMETERS Primary phases Secondary phases Kinetics of dissolution / precipitation Phase Volume % Calcite72.12 Portlandite5.73 CSH Monocarboaluminate2.26 Ettringite3.60 Hydrotalcite0.39 Hydrogarnet-Fe (C3FH6)2.05 Phase typePhases OxidesMagnetite, Amorphous silica HydroxidesBrucite, Gibbsite, Fe(OH) 3 Sheet silicatesSepiolite Other silicatesCSH 1.2, CSH 0.8, Straetlingite, Katoite_Si Sulfates, chlorides, other saltsGypsum, Anhydrite, Burkeite, Syngenite, Glaserite, Arcanite, Glauberite, Polyhalite CarbonatesCalcite, Nahcolite OtherHydrotalcite-CO 3, Ettringite, Dawsonite amorphous CSH phases

CARBONATION RESULTS pH decrease, portlandite dissolution and calcite precipitation over a thickness of about 2 cm after 100 years

CARBONATION RESULTS Dissolution of CSH 1.6, ettringite, monocarboaluminate and hydrotalcite on 2 cm after 100 years Precipitation of CSH 1.2, CSH 0.8, straetlingite, amorphous silica and gypsum on the same thickness Precipitation of small amounts of sepiolite, gibbsite and katoïte-Si is also predicted

CARBONATION RESULTS from a performance assessment point of view: looking at the different concrete performance  similar paragenesis  from 1 cm to 4 cm after 100 years sensitivity calculations on diffusion properties a and b (tortuosity parameters)  less than 1 cm (a, b +50% with HPC) in 100 years  complete carbonation cm - (a, b -50% with LPC) in 25 years

CARBONATION RESULTS: COMPARISON WITH EXPERIMENTAL RESULTS Modeling results - alteration is complete (amorphous silica) - no residual primary phases (portlandite)

CARBONATION RESULTS: COMPARISON WITH EXPERIMENTAL RESULTS Modeling results - alteration is complete (amorphous silica) - no residual primary phases (portlandite) Experimental results - residual primary phases (portlandite)  alteration is not complete Intensity (a.u.) Distance (mm) Calcite front Portlandite front Drouet, 2010

CARBONATION RESULTS Effect of water content on reactivity (Bazant type function) 2nd MAJOR COUPLING EFFECT!! S liq diffusion chemical reactivity

CARBONATION RESULTS Effect of water content on reactivity (Bazant type function) 2nd MAJOR COUPLING EFFECT!! S liq diffusion chemical reactivity

CARBONATION RESULTS Significant reduction in the amplitude of carbonation (less dissolution of portlandite and CSH 1.6 and less precipitation of amorphous silica and other secondary CSH) Lower reactivity accompanied by a greater penetration of carbonation front due to lower consumption of CO 2 at the surface Effect of water content on reactivity (Bazant type function)

CARBONATION RESULTS Significant reduction in the amplitude of carbonation (less dissolution of portlandite and CSH 1.6 and less precipitation of amorphous silica and other secondary CSH) Lower reactivity accompanied by a greater penetration of carbonation front due to lower consumption of CO 2 at the surface Effect of water content on reactivity (Bazant type function)

CARBONATION RESULTS Significant reduction in the amplitude of carbonation (less dissolution of portlandite and CSH 1.6 and less precipitation of amorphous silica and other secondary CSH) Lower reactivity accompanied by a greater penetration of carbonation front due to lower consumption of CO 2 at the surface Effect of water content on reactivity (Bazant type function)

CONCLUSIONS Drying process of 11 cm thick waste packages depends strongly on the concrete nature and slightly on the flow model (Richards or full multiphase) Considering full multiphase model, carbonated depth is about 2 cm after 100 years for the Intermediate Performance Concrete.  degraded thickness is totally carbonated (total dissolution of primary mineral phases) If we consider a chemical reactivity depending on the liquid saturation (Bazant type function), a considerable reduction in the amplitude of carbonation and a greater penetration of carbonation front are observed  calibration with accelerated carbonation experiments (Drouet, 2010) also: need for improved knowledge on kinetics parameters and thermodynamic data, especially for CSH with low Ca/Si ratio Other perspectives include: taking into account a protective effect of secondary minerals modeling corrosion of rebars