Coupled Chemo-Hydro-Mechanical analysis of Bituminized Waste swelling due to water up-taking

Bituminized Waste materials (BW) were produced by an industrial reprocessing of radioactive waste qualified low or medium activity and long life (LA-LL and MA-LL). BW is composed of precipitation sludge from the chemical reprocessing of spent nuclear fuel, immobilised in bitumen matrix. Geological storage is the reference solution for this kind of wastes. Under geological disposal conditions, and after a period of hundred thousand years, BW will undergo water re-saturation from host rock. Water up-tacking by BW will first induced free swelling in order to fill all different types of void existing in the storage disposal (void in primary canister, void in concrete container and void in rock vault). Then eventually swelling in contact with host rock and under special stress conditions. That's why the study of the behaviour of this type of material is very-important. Bituminized waste can be considered as a very-low permeable material containing one or several salt crystals. In order to describe the behaviour of such a material in contact of water, several mechanisms has to be coupled. The aim of this work is to study theses coupling during water up-tacking. Swelling behaviour in contact of water is govern by two principal mechanisms. First mechanism is the solvent transport leading to the dissolution of salt crystals. During dissolution, salt crystals volume increases, leading to global swelling of the bitumen matrix. Second mechanism is osmotic flow, which is leading directly to an overpressure in pore water due to chemical gradient (osmotic pressure) A model based on classical poromechanical approach has been developed in order to evaluate which is the leading mechanism and to study all the coupling. The chemical part of this model manage the precipitation/dissolution of salt crystals present in the bitumen matrix. It is the principal driving force of water up-taking, leading to salt saturation in pore water and increasing the porosity. That create a chemical gradient (salt concentration gradient) between pore water and host rock's water. Which initiate osmotic phenomenon: the bitumen matrix play the role of semi-permeable membrane allowing increasing of pore water pressure in the bituminized waste (osmotic overpressure). Over wise the porosity created by the salt crystals dissolution allow advectif and diffusive transport of water and salt through the bitumen matrix. The mechanical behaviour is strongly dominated by creep-deformation needing viscoplastic deformation management. A chemo-hydro mechanical numerical model in one dimension has been implemented (finite volume) in order to evaluate all mechanisms and coupling. This numerical model has shown that osmosis is the principal mechanism of water up-taking and that other mechanisms are not negligible. Moreover the difference of behaviour and coupling importance has been studied during both free swelling and water up-taking under constant volume. This work permitted us to find which parameters are needed to be identified experimentally

Effect of damage on water retention and gas transport properties geomaterials : Application to geological storage of radioactive waste

Dans le contexte du stockage géologique des déchets radioactifs, ce travail contribue à la caractérisation de l’effet de l’endommagement diffus sur les propriétés de rétention d’eau et transfert de gaz (perméabilité et percée de gaz). Les matériaux considérés sont les bétons CEM I et CEM V sélectionnés par l’Andra, l’argilite du Callovo-Oxfordien (roche hôte) et les interfaces argilite/béton. Cette étude a fourni des informations sur la microstructure des bétons à partir de leurs propriétés de rétention d’eau mais également à partir de la porosimétrie au mercure. Chaque béton a une microstructure bien distincte, caractérisée par une proportion non négligeable de pores capillaires pour le CEM I et une grande proportion de pores des hydrates pour le CEM V. Plusieurs protocoles d’endommagement ont été développés. L’endommagement contribue à réduire la capacité de rétention d’eau du béton CEM I et à augmenter leur perméabilité au gaz. En revanche, tous les échantillons endommagés présentent une pression de percée au gaz significativement plus faible que celles des matériaux sains, et ceci quel que soit le type de béton. Pour l’argilite, on observe une prise d’eau progressive à HR=100%, qui engendre un endommagement du matériau. Ce dernier réduit sa capacité de rétention d’eau. Par ailleurs, ses propriétés de rétention d’eau et de transport de gaz dépendent fortement de son état hydrique initial ainsi que de son endommagement. Enfin, on observe un phénomène de colmatage au niveau des interfaces, d’abord mécanique, puis hydraulique (et surement chimique) suite à l’injection d’eau. Ceci a pour conséquence de réduire la pression de percée des échantillons d’interfaceIn the context of geological disposal of radioactive waste, this work contributes to the characterization of the effect of diffuse damage on the water retention and gas transfer properties of concrete (CEM I and CEM V) selected by Andra, Callovo-Oxfordian argillite (host rock) and argillite / concrete interfaces. This study provides information on the concrete microstructure from Mercury porosimetry intrusion and water retention curves: each concrete has a distinct microstructure, CEM I concrete is characterized by a significant proportion of capillary pores while CEM V concrete has a large proportion of C-S-H pores. Several protocols have been developed in order to damage concrete. The damage reduces water retention capacity of CEM I concrete and increases its gas permeability. Indeed, gas breakthrough pressure decreases significantly for damaged concrete, and this regardless of the type of concrete. For argillite, the sample mass increases gradually at RH = 100%, which creates and increases damage in the material. This reduces its ability to retain water. Otherwise, water retention and gas transport properties of argillite are highly dependent of its initial water saturation, which is linked to its damage. Finally, we observed a clogging phenomenon at the argillite/concrete interfaces, which is first mechanical and then hydraulic (and probably chemical) after water injection. This reduces the gas breakthrough pressure interface

Impact de la fissuration sur les propriétés de rétention d‘eau et de transport de gaz des géomatériaux : Application au stockage géologique des déchets radioactifs

In the context of geological disposal of radioactive waste, this work contributes to the characterization of the effect of diffuse damage on the water retention and gas transfer properties of concrete (CEM I and CEM V) selected by Andra, Callovo-Oxfordian argillite (host rock) and argillite / concrete interfaces. This study provides information on the concrete microstructure from Mercury porosimetry intrusion and water retention curves: each concrete has a distinct microstructure, CEM I concrete is characterized by a significant proportion of capillary pores while CEM V concrete has a large proportion of C-S-H pores. Several protocols have been developed in order to damage concrete. The damage reduces water retention capacity of CEM I concrete and increases its gas permeability. Indeed, gas breakthrough pressure decreases significantly for damaged concrete, and this regardless of the type of concrete. For argillite, the sample mass increases gradually at RH = 100%, which creates and increases damage in the material. This reduces its ability to retain water. Otherwise, water retention and gas transport properties of argillite are highly dependent of its initial water saturation, which is linked to its damage. Finally, we observed a clogging phenomenon at the argillite/concrete interfaces, which is first mechanical and then hydraulic (and probably chemical) after water injection. This reduces the gas breakthrough pressure interfacesDans le contexte du stockage géologique des déchets radioactifs, ce travail contribue à la caractérisation de l’effet de l’endommagement diffus sur les propriétés de rétention d’eau et transfert de gaz (perméabilité et percée de gaz). Les matériaux considérés sont les bétons CEM I et CEM V sélectionnés par l’Andra, l’argilite du Callovo-Oxfordien (roche hôte) et les interfaces argilite/béton. Cette étude a fourni des informations sur la microstructure des bétons à partir de leurs propriétés de rétention d’eau mais également à partir de la porosimétrie au mercure. Chaque béton a une microstructure bien distincte, caractérisée par une proportion non négligeable de pores capillaires pour le CEM I et une grande proportion de pores des hydrates pour le CEM V. Plusieurs protocoles d’endommagement ont été développés. L’endommagement contribue à réduire la capacité de rétention d’eau du béton CEM I et à augmenter leur perméabilité au gaz. En revanche, tous les échantillons endommagés présentent une pression de percée au gaz significativement plus faible que celles des matériaux sains, et ceci quel que soit le type de béton. Pour l’argilite, on observe une prise d’eau progressive à HR=100%, qui engendre un endommagement du matériau. Ce dernier réduit sa capacité de rétention d’eau. Par ailleurs, ses propriétés de rétention d’eau et de transport de gaz dépendent fortement de son état hydrique initial ainsi que de son endommagement. Enfin, on observe un phénomène de colmatage au niveau des interfaces, d’abord mécanique, puis hydraulique (et surement chimique) suite à l’injection d’eau. Ceci a pour conséquence de réduire la pression de percée des échantillons d’interfac

Impact de la fissuration sur les propriétés de rétention d eau et de transport de gaz des géomatériaux (Application au stockage géologique des déchets radioactifs)

Dans le contexte du stockage géologique des déchets radioactifs, ce travail contribue à la caractérisation de l effet de l endommagement diffus sur les propriétés de rétention d eau et transfert de gaz (perméabilité et percée de gaz). Les matériaux considérés sont les bétons CEM I et CEM V sélectionnés par l Andra, l argilite du Callovo-Oxfordien (roche hôte) et les interfaces argilite/béton. Cette étude a fourni des informations sur la microstructure des bétons à partir de leurs propriétés de rétention d eau mais également à partir de la porosimétrie au mercure. Chaque béton a une microstructure bien distincte, caractérisée par une proportion non négligeable de pores capillaires pour le CEM I et une grande proportion de pores des hydrates pour le CEM V. Plusieurs protocoles d endommagement ont été développés. L endommagement contribue à réduire la capacité de rétention d eau du béton CEM I et à augmenter leur perméabilité au gaz. En revanche, tous les échantillons endommagés présentent une pression de percée au gaz significativement plus faible que celles des matériaux sains, et ceci quel que soit le type de béton. Pour l argilite, on observe une prise d eau progressive à HR=100%, qui engendre un endommagement du matériau. Ce dernier réduit sa capacité de rétention d eau. Par ailleurs, ses propriétés de rétention d eau et de transport de gaz dépendent fortement de son état hydrique initial ainsi que de son endommagement. Enfin, on observe un phénomène de colmatage au niveau des interfaces, d abord mécanique, puis hydraulique (et surement chimique) suite à l injection d eau. Ceci a pour conséquence de réduire la pression de percée des échantillons d interfaceIn the context of geological disposal of radioactive waste, this work contributes to the characterization of the effect of diffuse damage on the water retention and gas transfer properties of concrete (CEM I and CEM V) selected by Andra, Callovo-Oxfordian argillite (host rock) and argillite / concrete interfaces. This study provides information on the concrete microstructure from Mercury porosimetry intrusion and water retention curves: each concrete has a distinct microstructure, CEM I concrete is characterized by a significant proportion of capillary pores while CEM V concrete has a large proportion of C-S-H pores. Several protocols have been developed in order to damage concrete. The damage reduces water retention capacity of CEM I concrete and increases its gas permeability. Indeed, gas breakthrough pressure decreases significantly for damaged concrete, and this regardless of the type of concrete. For argillite, the sample mass increases gradually at RH = 100%, which creates and increases damage in the material. This reduces its ability to retain water. Otherwise, water retention and gas transport properties of argillite are highly dependent of its initial water saturation, which is linked to its damage. Finally, we observed a clogging phenomenon at the argillite/concrete interfaces, which is first mechanical and then hydraulic (and probably chemical) after water injection. This reduces the gas breakthrough pressure interfacesVILLENEUVE D'ASCQ-ECLI (590092307) / SudocSudocFranceF

Water Retention and Gas Migration of Two High-Performance Concretes after Damage

International audienceIn the context of long-term repository of high-level and long-lived nuclear waste, authors investigate different concrete properties related to fluid transport, in order to determine which is able to detect damage earliest. To this purpose, different protocols are tested, which impose progressive damage to two different Andra high-performance concretes (HPCs), based on pure portland (CEMI) or composed cement (CEMV)-type cements. The properties investigated are pore size distributions and porosity [by mercury intrusion porosimetry (MIP)], water retention curves, relative gas permeability, and gas migration properties (gas breakthrough pressure). Gas breakthrough pressure (GBP) is assessed rather than gas entry, by accurately measuring gas presence on the downstream side of a confined sample subjected to slowly increasing gas pressure on its upstream side. From MIP data, authors show that CEMI concrete has smaller porosity but greater pore sizes than CEMV. For CEMI concrete, all damage procedures significantly affect water retention curves and gas breakthrough pressures, yet they have no effect upon the relationship between relative gas permeability and water saturation. For CEMV concrete subjected to low damage levels, gas breakthrough measurements detect damage, whereas water retention and gas permeability do not

Characterization of transport and water retention properties of damaged Callovo-Oxfordian claystone

International audienceIn the context of the underground storage of radioactive waste, the aim of this experimental study is to characterize the effect of damage on transport and water retention properties of Callovo-Oxfordian (COx) argillite. The originality of the study is to simultaneously investigate the pore-size distribution, water retention, the dry, effective and relative gas permeability, and the gas breakthrough pressure (GBP) of damaged COx argillite. These different properties are all relevant to characterizing the fluid transport ability of COx argillite.Results show that the damage has a significant impact on the properties of the COx argillite. It induces a decrease in its water retention capacity and GBP, and it increases its gas permeability and apparent porosity available to water owing to the creation of micro-cracks.Another objective is to show which of these properties is the most suitable to detect early damage states in COx argillite, with a potential use being to identify them in situ. GBP appears to be the best ‘detector’ of damage because of its sensitivity to damage even under high confinement pressures. Gas permeability could be a good indicator of damage, as it increases significantly (one or several orders of magnitude) after the damage. Finally, the water permeability curve is a poor indicator of COx argillite damage

Chemo-Hydro-Mechanical analysis of Bituminized Waste swelling due to water uptake: Experimental and model comparisons

International audienceThis paper presents a numerical model developed to reproduce the behaviour of French simplified Bituminized Waste Products (BWP) during a leaching test. The model is calibrated on experimental data sets. BWP were mainly produced during industrial reprocessing of nuclear spent fuel and are classified as low or intermediate activity long lived radioactive waste. Geological disposal is the reference solution for intermediate level long-lived BWP. Under geological disposal facility conditions, and after a long period of time, BWP will undergo water re-saturation from the host rock. A chemo-hydro-mechanical numerical model has been implemented with a finite element scheme to model BWP behaviour under such conditions. The constitutive model takes into account the impact of dissolution, permeation, diffusion and osmosis. Original evolution laws of diffusion coefficient and permeability as a function of the porosity are proposed. Specific mechanical model is proposed including Mori-Tanaka homogenization law. To simulate the hydration of the material, an original and simple method is proposed, avoiding costly two-phase flow resolution and complex calibration of the related parameters. This model was mainly used to reproduce the evolution of the amount of both water absorbed and salt leached by the sample during unconfined water up-taking tests. The calibration is based on experimental data obtained on French simplified BWP containing one highly soluble salt. Water uptake could generate swelling mainly due to osmosis