Search

In the context of deep waste disposals, the geological barrier (i.e., the host rock) will be exposed to saline plumes from bituminous waste and alkaline plumes from concrete degradation. These chemical disturbances will affect the hydraulic and mechanical properties of the clay rock by modifying its microstructure. As a result, the self-sealing of the fractures created during excavation could be affected,further affecting the long-term safety of the repositories. To this end, the effect of salinity and alkalinity on the microstructure of a partially saturated Opalinus Clay from the lower sandy facies of Mont Terri was investigated. It was found that at 𝑤 = 4.1%, salinity decreases the density and the peak of the mesopores compared to the synthetic water. This is due to the water transfer from the meso to the macro pores and to the decrease of the thickness of the diffuse double layer. For the same water content, alkalinity generates meso and macro pores. The dissolutions of clay and non-clay minerals are the main mechanisms involved.

Some (saturated) claystones, considered as host rocks for deep radioactive waste disposal, are sensitive to drying and wetting. Wetting may result in swelling and damage during the resaturation of specimens for mechanical testing. Given that, due to evaporation, specimens may have lost some pore water during coring, transport, storage and trimming prior to lab testing, it is required to re-saturate them by reinjecting the evaporated water content, compressing the pore space under constant water content, or by using a combination of both. It is important to characterize the hydromechanical processes involving suction changes under total stress loading in order to adapt preparation methods and minimize sample disturbances. We present a novel experimental setup to test claystone specimens under isotropic compression at constant water content, while measuring suction, and we discuss the data of three specimens testedat different initial suctions and degrees of saturation. Interestingly, the path followed in the (decreased) suction vs (increased) total confining stress diagram was observed to be close to the Gens-Alonso “Neutral Line” (a line inclined of 45° in a suction/mean total stress diagram, illustrating similar effects of changes of both variables). In other words, even in close to saturated conditions, changes in confining stress resulted in comparable changes in suction. The data obtained indicate that applying a total stress of 12.2 MPa during resaturation keeps the material on the compressive side of the Neutral Line, limiting swelling-induced sample disturbance.

Significant interest has been devoted to claystones and shales in the context of geological radioactive waste disposal at great depth. The determination of their mechanical properties is needed for appropriate design of the underground galleries and tunnels. Given their high sensitivity to changes in water content, special care has to be taken so as to provide characteristics as close as possible to the (saturated) insitu ones. Based on the hydromechanical path followed by samples from coring to trimming in the lab, that most often lead to some degree of desaturation resulting from evaporation and drying of the samples, some procedures aimed at minimising the resulting perturbations are described. The considerations presented are based on data obtained on two (swelling) claystones considered in Europe for deep geological disposal, i.e., the Callovo-Oxfordian claystone (France) and the Opalinus Clay (Switzerland).

Based on tests carried out on a specific device allowing to determine the water retention and transport properties of granular media at low suctions, an alternative approach to Kunze and Kirkham’s method of accounting for the impedance effects due to the high air entry value ceramic disk when using Gardner’s method is proposed. Impedance effects are accounted for by proposing analytical solutions to the equations governing water transfers occurring within the specimen and the ceramic disk. By using some experimental data obtained on a volcanic granular substrate used for urban green roofs, the method is successfully compared to Kunze and Kikham’s graphical method. Its advantages are to be simpler of use and not operator dependent. A detailed examination of the performance of our method compared to those of Gardner and Kunze and Kirkham is carried out based on experimental data, that confirm its validity.

This paper describes six projects, most of which are part of the research portfolio of the EERA JPNM, devoted to qualification, modelling and development of structural and fuel materials for advanced and innovative nuclear systems, with also two examples of projects addressing issues of cross-cutting interest through fusion and fission. The main conclusion is that the benefit of the coordination under the umbrella of, in this case, the EERA JPNM, is clearly felt in terms of better alignment of national programmes and subsequent leveraging of institutional funding, to integrate Euratom support. Likewise, the benefit of addressing specific issues of common interest for fusion and fission is not only beneficial because of cross-fertilisation, but also because it allows more rational use of human and infrastructural resources, avoiding duplications.

The water retention curve and the hydraulic conductivity function of a volcanic coarse granular material used as a substrate in an urban green roof in the Paris area was carried out on a newly developed device, in which low suctions were controlled. In the same cell, a hanging column system was used for controlling smaller suctions (up to 32 kPa) and the axis translation technique for larger suctions (up to 50 kPa). Water exchanges were monitored in connected tubes by using a high accuracy differential pressure transducer. The step changes in suction were also used to determine the hydraulic conductivity function by means of Gardner’s method, accounting for the impedance effects due to the high air entry value ceramic porous disk with Kunze and Kirkham’s method. van Genuchten and Brooks and Corey models were used for the water retention curve, but the hydraulic conductivity functions derived from these expressions appeared to lead to a significant under-estimation, confirming the need of operational and simple device for the experimental determination of the hydraulic conductivity function.

In thermally enhanced recovery processes like Cyclic Steam Stimulation (CSS) or Steam Assisted Gravity Drainage (SAGD), continuous steam injection entails changes in pore fluid, pore pressure and temperature in the rock reservoir, that are most often unconsolidated or weakly consolidated sandstones. This in turn increases or decreases the effective stresses and changes the elastic properties of the rocks. Thermally enhanced recovery processes give rise to complex couplings. 4D seismic surveys are currently conducted to delineate the steam-affected areas but the interpretation is difficult. However, it is essential for optimization of reservoir development. Numerical simulations have been carried out on a case study so as to provide an estimation of the evolution of pressure, temperature, pore fluid saturation, stress and strain in any zone located around the injector and producer wells. The approach of Ciz and Shapiro (2007) (Geophysics 72, A75-A79) has been used to model the velocity dispersion in the oil sand mass under different conditions of temperature and stress. A good agreement has been found between these predictions and some laboratory velocity measurements carried out on samples of Canadian oil sand. Results appear to be useful to better interpret 4D seismic data in order to locate the steam chamber. Dans les procédés de récupération des huiles lourdes par méthodes thermiques, comme ia stimulation cyclique par vapeur (CSS) ou le drainage par gravité assisté par vapeur (SAGD), l’injection de vapeur en continu entraîne des changements de liquide de pores, de pression interstitielle et de température dans la roche réservoir, qui est constituée le plus souvent de sable non consolidés ou faiblement consolidés- Ces changements à leur tour augmentent ou diminuent les contraintes effectives et modifient les propriétés élastiques des roches. Les procédés de récupération par méthodes thermiques mettent en oeuvre des couplages complexes. Des campagnes de sismique 4D sont couramment effectuées pour suivre les zones affectées par la vapeur, mais leur interprétation est difficile, Elle est pourtant essentielle pour optimiser le développement du réservoir. Des simulations numériques ont été réalisées sur un cas d’étude afin de fournir une estimation de l’évolution des pressions, températures, saturation des fluides interstitiels, contraintes et déformations dans toute zone située autour des puits injecteur et producteur. L’approche de Ciz et Shapiro (2007) (Geophysics 72, A75-A79) a été utilisée pour modéliser la dispersion de vitesse dans les sables bitumineux sous différentes conditions de température et de contrainte. Un bon accord a été trouvé entre les prédictions du modèle et certaines mesures de vitesse effectuées en laboratoire sur des échantillons de sables bitumineux Canadiens. Les résultats sont utiles pour mieux interpréter les données sismiques 4D afin de localiser la chambre à vapeur.

La complexité syntaxique d’une phrase en langage oral peut se caractériser par le nombre et la nature des opérations syntaxiques nécessaires à son élaboration, et notamment par la profondeur de son enchâssement. Cette complexité influence l’âge d’acquisition des différentes structures syntaxiques, les énoncés les plus complexes étant maîtrisés plus tardivement par l’enfant. Certains auteurs attribuent cette acquisition de la syntaxe complexe à des contraintes développementales externes au système linguistique lui-même et notamment à des limitations dans les capacités de mémoire de travail (Jakubowicz, 2007). Ainsi, le traitement d’une phrase complexe engendrerait un coût cognitif important et constituerait une surcharge pour des capacités de mémoire de travail davantage limitées chez le jeune enfant. La maturation normale de ce système mnémonique permettrait ensuite à l’enfant de comprendre et de produire des énoncés de plus en plus complexes. La présente recherche a pour objectif d’éclaircir les liens entre le développement de la mémoire de travail et le traitement des phrases complexes chez l’enfant tout-venant âgé de 5 à 12 ans. Suivant le modèle de la mémoire de travail de Baddeley & Hitch (1986) et les travaux de Barrouillet & Camos (2001, 2007), nous avons appréhendé les compétences de la boucle phonologique via des épreuves d’empans simples (empan direct de chiffres, répétition de mots et de pseudo-mots) et la mémoire de travail verbale via des tâches d’empans complexes (empan indirect de chiffres, counting span et running span). Les habiletés syntaxiques des enfants ont été évaluées en compréhension et en répétition d’énoncés complexes. Une analyse d’échantillons de langage spontané a enfin permis de récolter les données liées à l’utilisation de la syntaxe complexe en contexte écologique (LME, taux de subordination et taux d’enchâssement profond). Les résultats de 48 enfants francophones monolingues, répartis en trois groupes d’âge (5-6, 8-9 et 11-12 ans), révèlent des corrélations fortes entre les scores des empans simples et complexes et les performances syntaxiques. Plus précisément, nous avons pu démontrer la valeur hautement prédictive des compétences en mémoire de travail sur l’acquisition des habiletés morphosyntaxiques en réception et en production. Ainsi, le score composite des empans complexes explique 48% de la variance des scores en compréhension syntaxique et de 16 à 30% des mesures obtenues en production spontanée. Nos résultats soutiennent donc l’hypothèse selon laquelle l’augmentation des capacités de mémoire de travail permettrait à l’enfant une maîtrise progressive des phrases complexes. L’existence d’une relation causale réciproque reste cependant à explorer.

The radiological characterization of contaminated elements (walls, grounds, objects) from nuclear facilities often suffers from too few measurements. In order to determine risk prediction bounds on the level of contamination, some classic statistical methods may therefore be unsuitable, as they rely upon strong assumptions (e.g., that the underlying distribution is Gaussian) which cannot be verified. Considering that a set of measurements or their average value come from a Gaussian distribution can sometimes lead to erroneous conclusions, possibly not sufficiently conservative. This paper presents several alternative statistical approaches which are based on much weaker hypotheses than the Gaussian one, which result from general probabilistic inequalities and order-statistic based formulas. Given a data sample, these inequalities make it possible to derive prediction intervals for a random variable which can be directly interpreted as probabilistic risk bounds. For the sake of validation, they are first applied to simulated data generated from several known theoretical distributions. Then, the proposed methods are applied to two data sets obtained from real radiological contamination measurements.

Stress release effects in a specimen of claystone extracted at great depth (465 m) in the layer of the Callovo-Oxfordian claystone in Eastern France is examined by mimicking the stress change during extraction in the oedometer. To do so, a specimen first submitted to hydration with swelling impeded is afterwards unloaded at constant water content. Comparable mercury intrusion pore size distribution curves are obtained before and after stress release, showing little change in the configuration of inter-platelets pores within the clay matrix of the claystone. The swelling observed at constant water content is then related, to a water transfer from inter-platelets pores to intra-platelets pores, resulting in crystalline swelling within the smectite fraction of the inter-layer illite-smectite minerals.

The effect of changes in suction on the microstructure of the Callovo-Oxfordian claystone along wetting and drying paths was investigated by using mercury intrusion porosimetry. Based on a simplified brick model, the changes of the average thickness of the platelets that constitute the clay matrix (50%) are interpreted as the consequence of the successive adsorption of ordered layers of water molecules along the smectite surfaces, as demonstrated on pure smectites for a long time. This shows the predominant role played by the smectite phase in the overall response of the Callovo-Oxfordian claystone when submitted to suction changes under no stress.

The steam assisted gravity drainage (SAGD) is a thermal in-situ technology that has been successfully used to enhance the recovery of heavy oil and bitumen in the Western Canada and in the Eastern Venezuela basins. Pressure and temperature variations during SAGD operations induce complex changes in the mechanical and acoustic properties of the reservoir rocks as well as of the caprock. To study these changes, measurements of ultrasonic wave velocities Vp, Vs were performed on both reconstituted samples and natural samples from oil sands reservoir. Reconstituted samples were made of Fontainebleau sands with a slight cementation formed by a silicate solution. They have a high porosity (about 30 % to 40 %) and a high permeability (up to 10 D). Natural oil sands samples are unconsolidated sandstones extracted from the fluvio-estuarine McMurray Formation in Alberta (Canada). The saturating fluids were bitumen and glycerol with a strongly temperature dependent viscosity. The tests were carried out at different temperatures (in the range 40° and +86°C) and at different effective pressures (from 12 bars up to 120 bars). Experimental results firstly showed that the elastic wave propagation velocities measured are strongly dependent on temperature and pore fluid viscosity whereas little effect of effective pressure was observed. Velocities decreased with increasing temperature and increased with increasing effective pressure. These effects are mainly due to the variations of the saturating fluids properties. Finally, the tests were modelled by using Ciz and Shapiro (2007) approach and satisfactory velocities values were obtained with highly viscous fluids, a case that cannot be easily explained by using the poro-elastic theory of Biot-Gassmann.