Porosity 0.13 Aqueous diffusion
D0 (m².s-1) 2.10-9
Intrinsic permeability (m²)
Water Gas
2.10-22 4.10-17
Gaseous diffusion D0 (m².s-1)
1.10-5
van Genuchten Pr (Pa) 2.107 Millington Quirk a 2.0
van Genuchten n 0.491 Millington Quirk b 4.2
Slr – Slmax - Sgr 0.0 - 1.0 - 0.0
50 years
0,00
0,02
0,04
0,06
0,08
0,10
0,12
0,14
0 0,01 0,02 0,03 0,04 0,05 0,06Distance (m)
Vo
lum
e F
rac
tio
n
CSH 1.6
Portlandite
Ettringite
Monocarboaluminate
C3FH6
Hydrotalcite
Comparison of modeling approaches to atmospheric carbonation of concrete in the context of deep
geological disposal of Intermediate Level Waste O. Bildstein(1), P. Thouvenot(1), L. Trotignon(1), S. Poyet(2), B. Cochepin(3) and I. Munier(3)
(1) CEA, DEN, DTN/SMTM/LMTE, 13108 Saint-Paul-lez-Durance – France
(2) CEA, DEN, DPC/SCCME/LECBA, 91191 Saclay – France
(3) ANDRA - 92298 Châtenay-Malabry Cedex - France
Context : long term behavior of materials in deep geological disposal of ILLWThe present design for the intermediate-level, long-lived radioactive waste (ILLW) is based on concrete structures and reinforced concrete waste packages placed into the deep Callovo-Oxfordian clay-stone geological formation. During the disposal operating period (up to 100 years) these concrete components will be subjected to ventilation in order to (1) guarantee operating safety and (2) contribute to the evacuation of residual heat from the exothermic waste. The ventilated air, drawn from the surface, will generate a partial drying of the concrete components as well as the development of atmospheric carbonation. These processes may potentially lead to a progressive lowering of pH inside the cement paste and trigger corrosion of the steel reinforcement, contributing to a global deleterious effect on the concrete integrity.
Conclusions
2 approaches are compared : a complete multiphase model (TOUGH2-EOS4) and a model based on Richards equation (TOUGH2-EOS9 and CAST3M)
Model description
(Andra, 2005)
The carbonation process is difficult to simulate especially due to the overall tendency of models to underestimate the CSH transition to lower C/S values and to precipitate amorphous silica early in the simulation. Both codes indicate similar paragenesis but with a sharper front for TOUGHREACT. Some differences remain concerning the evolution of minerals such as monocarboaluminate and Fe(OH)3
New simulations should take the effect of water saturation into account for the calculation of mineral reactivity
The dynamics of the concrete drying process is captured by the different codes with different modelling approaches (multiphase vs. Richards). Special attention has to be paid to the choice of the water vapour diffusion coefficient because this process may significantly participate to the overall drying rate and the water saturation profile
During drying of the concrete, atmospheric carbonation in unsaturated conditions involves intricate couplings between capillary flow, transport of both vapour and liquid water as well as aqueous and gaseous CO2. Chemical reactions lead, in the same time, to the alteration of the cement hydrates (reactions with dissolved CO2).
In order to model the waste package carbonation, a 1D half section of the container (section = 0.11 m) is represented, with atmospheric carbonation occurring on the left face.
The drying process
The carbonation process
▲ Results obtained with EOS9 and CAST3M are in good agreement (2 codes with the same physics)
2 different approaches are compared : a complete multiphase reactive model
(TOUGHREACT-EOS4) and a unsaturated (constant saturation
distribution) reactive model (CRUNCH)
0,15
0,25
0,35
0,45
0,55
0,65
0,75
0,85
0,00 0,01 0,02 0,03 0,04 0,05 0,06Distance (m)
Liq
uid
Sa
tura
tio
n
t = 0 year
Cast3m t = 1 year
Cast3m t = 2 years
Cast3m t = 5 years
Cast3m t = 10 years
Cast3m t = 20 years
Cast3m t = 50 years
Cast3m t = 100 years
TR EOS9 t = 1 year
TR EOS9 t = 2 years
TR EOS9 t = 5 years
TR EOS9 t = 10 years
TR EOS9 t = 20 years
TR EOS9 t = 50 years
TR EOS9 t = 100 years
0,15
0,25
0,35
0,45
0,55
0,65
0,75
0,85
0,00 0,01 0,02 0,03 0,04 0,05 0,06Distance (m)
Liq
uid
Sa
tura
tio
n
t = 0
TR EOS9 t = 1 year
TR EOS9 t = 2 years
TR EOS9 t = 5 years
TR EOS9 t = 10 years
TR EOS9 t = 20 years
TR EOS9 t = 50 years
TR EOS9 t = 100 years
TR EOS4 t = 1 year
TR EOS4 t = 2 years
TR EOS4 t = 5 years
TR EOS4 t = 10 years
TR EOS4 t = 20 years
TR EOS4 t = 50 years
0,15
0,25
0,35
0,45
0,55
0,65
0,75
0 0,01 0,02 0,03 0,04 0,05 0,06Distance (m)
Liq
uid
Sa
tura
tio
n
TR EOS9 t = 1 year
TR EOS9 t = 2 years
TR EOS9 t = 5 years
TR EOS9 t = 10 years
TR EOS9 t = 20 years
TR EOS9 t = 50 years
TR EOS9 t = 100 years
TR EOS4 Dgaz/10 t = 1 year
TR EOS4 Dgaz/10 t = 2 years
TR EOS4 Dgaz/10 t = 5 years
TR EOS4 Dgaz/10 t = 10 years
TR EOS4 Dgaz/10 t = 20 years
TR EOS4 Dgaz/10 t = 50 years
TR EOS4 Dgaz/10 t = 100 years
50 years
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0,02
0,04
0,06
0,08
0,10
0,12
0,14
0,16
0,18
0 0,005 0,01 0,015 0,02 0,025 0,03Distance (m)
Vo
lum
e F
ract
ion
Calcite
amorphous silica
CSH 0.8
Fe(OH)3
Sepiolite
Gypsum
Gibbsite
◄ A fairly good agreement is reached between the drying
dynamics upon using a 10 times lower value for the diffusion coefficient in the gas phase in EOS4
depending on the diffusion coefficient, the drying process is not entirely controlled by water advection
▲ Results obtained with EOS4 and EOS9 are quite different: the diffusion of water in the gas phase (EOS4) contributes to a faster drying front from the surface towards the inner part of the waste container. This latter part also reaches lower water saturation
◄ Primary mineral phases : the overall behaviour ► of both models is similar, but results obtained with TOUGHREACT show a sharper front than in CRUNCH. The dissolution front is the same in both cases except for monocarboaluminate which dissolves much further ahead with CRUNCH
◄ Secondary mineral phases : the same sharp ► front observed with EOS4. The results obtained with CRUNCH show a much smoother front with a less complete portlandite to calcite transformation. Also, intermediate CSH phases are not stable in CRUNCH and are replaced by straetlingite at the front
Waste disposal package
Disposal cell
Protection airlock
(dual gate system) Access drift
Waste disposal package
Concrete lid
Concrete overpack
Primary waste package
to
to
1.3
to
2.9
m1.
2 to
2.2
5 m
ToughReactCrunch
Dry air
(Rh = 40 %)
T = 25°C to 50°C
SlWater vapor diffusion
CO2 gas diffusionAqueous diffusion of reactants
Two phase water/air flow
Dissolution/precipitation : porosity reduction, permeability variations
Brine formation
CO2 gas dissolution
Dry air
(Rh = 40 %)
T = 25°C to 50°C
SlWater vapor diffusion
CO2 gas diffusionAqueous diffusion of reactants
Two phase water/air flow
Dissolution/precipitation : porosity reduction, permeability variations
Brine formation
CO2 gas dissolution
Millington Quirk : D = D0 a+1 Sl b
50 years
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0,08
0,10
0,12
0,14
0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07Distance (m)
Vo
lum
e F
ract
ion
CSH_1.6
Portlandite
Ettringite
Monocarboaluminate
C3FH6
Hydrotalcite
50 years
0,00
0,02
0,04
0,06
0,08
0,10
0,12
0,14
0,16
0,18
0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07Distance (m)
Vo
lum
e F
ract
ion
Calcite
Amorphous silica
Straetlingite
Fe(OH)3
Sepiolite
Gypsum