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In the framework of studies for the disposal of radioactive waste, ONDRAF/NIRAS, the Belgian National Agency for Radioactive Waste and enriched Fissile Materials investigates the option of a geological repository. In a geological repository, the waste is sidelined within a deep and stable geological layer, named host rock, behind a whole series of artificial barriers. Together, natural and artificial barriers ensure the isolation of waste, their confinement and the delay and spread of release of radioactive substances. The interaction of the host rock and the concrete support of disposal galleries is investigated to analyse the long-term sustainability of the structure. The host rock considered in this study is a poorly indurated clay present in the northern part of the Belgium, the Boom Clay. The behaviour of the interface between the Boom Clay and the concrete of the galleries is studied experimentally from both mechanical and gas transfer perspectives. Samples have been prepared consisting of two half cylinders, one made of concrete and the other one of Boom Clay to obtain an interface. A dedicated device has been designed using an HOEK type cell, which allow applying confining pressure to simulate lithostatic loading, injecting gas to measure transfer properties and generating relative displacement of both sides of the interface. Mechanical behaviour of the interface under short loading has first been studied. One originality of this study consists in using gas injection and Poiseuille’s law to monitor and quantify the opening and closure of the interface during mechanical loading. A partial irreversible closure of the interface and effects of long term loading have been observed. By increasing the confinement, the opening of the interface (clay-concrete) gradually decreases (initially 38 μm for 1.2 MPa of confining pressure) until it reaches 5 μm for 4.5 MPa. There is moderate expected irreversibility during unloading (19 μm at 1.7 MPa). The objective is to identify the main parameters allowing predicting the properties of the interface, such as initial roughness of the interface, water content, applied stress and time. The second part of the work consists in studying transfer properties at the interface. The aim is to identify paths available for gas produced during waste storage.

It is now established that a large extraterrestrial object hit the Earth at the end of the Cretaceous period, about 65 Ma ago. We have investigated Re-Os, Hf-W, and Mn-Cr isotope systems in sediments from the Cretaceous and the Paleogene in order to characterize the type of impactor. Within the Cretaceous-Tertiary (K-T) boundary layer, extraterrestrial material is mixed with terrestrial material, causing a dilution of the extraterrestrial isotope signature that is difficult to quantify. A phase essentially composed of Ni-rich spinel, formed in the atmosphere mainly from melted projectile material, is likely to contain the extraterrestrial isotopic signature of the impactor. We show that the analysis of spinel is indeed the best approach to determine the initial isotope composition of the impactor, and that W and Cr isotopes confirm that the projectile was a carbonaceous chondrite.

Magmatic iron meteorites are considered to be remnants of the metallic cores of differentiated asteroids, and may be used as analogues of planetary core formation. The Fe isotope compositions (δ 57/54Fe) of metal fractions separated from magmatic and non-magmatic iron meteorites span a total range of 0.39‰, with the δ 57/54Fe values of metal fractions separated from the IIAB irons (δ 57/54Fe 0.12 to 0.32‰) being significantly heavier than those from the IIIAB (δ 57/54Fe 0.01 to 0.15‰), IVA (δ 57/54Fe - 0.07 to 0.17‰) and IVB groups (δ 57/54Fe 0.06 to 0.14‰). The δ 57/54Fe values of troilites (FeS) separated from magmatic and non-magmatic irons range from - 0.60 to - 0.12‰, and are isotopically lighter than coexisting metal phases. No systematic relationships exist between metal-sulphide fractionation factor (Δ 57/54Fe M-FeS = δ 57/54Fe metal - δ 57/54Fe FeS) metal composition or meteorite group, however the greatest Δ 57/54Fe M-FeS values recorded for each group are strikingly similar: 0.79, 0.63, 0.76 and 0.74‰ for the IIAB, IIIAB, IAB and IIICD irons, respectively. Δ 57/54Fe M-FeS values display a positive correlation with kamacite bandwidth, i.e. the most slowly-cooled meteorites, which should be closest to diffusive equilibrium, have the greatest Δ 57/54Fe M-FeS values. These observations provide suggestive evidence that Fe isotopic fractionation between metal and troilite is dominated by equilibrium processes and that the maximum Δ 57/54Fe M-FeS value recorded (0.79 ± 0.09‰) is the best estimate of the equilibrium metal-sulphide Fe isotope fractionation factor. Mass balance models using this fractionation factor in conjunction with metal δ 57/54Fe values and published Fe isotope data for pallasites can explain the relatively heavy δ 57/54Fe values of IIAB metals as a function of large amounts of S in the core of the IIAB parent body, in agreement with published experimental work. However, sequestering of isotopically light Fe into the S-bearing parts of planetary cores cannot explain published differences in the average δ 57/54Fe values of mafic rocks and meteorites derived from the Earth, Moon and Mars and 4-Vesta. The heavy δ 57/54Fe value of the Earth's mantle relative to that of Mars and 4-Vesta may reflect isotopic fractionation due to disproportionation of ferrous iron present in the proto-Earth mantle into isotopically heavy ferric iron hosted in perovskite, which is released into the magma ocean, and isotopically light native iron, which partitions into the core. This process cannot take place at significant levels on smaller planets, such as Mars, as perovskite is only stable at pressures > 23 GPa. Interestingly, the average δ 57/54Fe values of mafic terrestrial and lunar samples are very similar if the High-Ti mare basalts are excluded from the latter. If the Moon's mantle is largely derived from the impactor planet then the isotopically heavy signature of the Moon's mantle requires that the impacting planet also had a mantle with a δ 57/54Fe value heavier than that of Mars or 4-Vesta, which then implies that the impactor planet must have been greater in size than Mars. © 2006 Elsevier B.V. All rights reserved.

International audience; HT-Lix0Co1-yMgyO2 (where x0 is the Li/(Co + Mg) ratio; x0 = 0.98, 1.0, 1.10; y = 0.0, 0.03, 0.06, and 0.10) materials were synthesized via a solid-state reaction. These samples were characterized by X-ray diffraction, 7Li MAS NMR spectroscopy, and electrical properties measurements. The XRD study showed that pure phases are obtained for 0.0 ≤ y < 0.10 and x0 ≥ 1.0. 7Li MAS NMR spectra of the Mg-doped phases exhibit two types of new signals at 55 ppm and 325, 7, −9, and − 27 ppm in addition to the signal at 0 ppm resulting from the presence of diamagnetic CoIII ions. On the basis of our general knowledge of Li NMR in layered oxides with electron spins, we suggest that Mg doping in LiCoO2 always leads to the simultaneous presence of CoIV ions (sharing an itinerant electron hole with neighboring CoIII ions) and, to a smaller extent, of intermediate spin Co3+(IS) ions trapped in a square-based pyramidal environment because of an oxygen vacancy. This feature is further enhanced by lithium overstoichiometry.