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International audience; Alteration experiments involving intermediate level nuclear waste (ILW) glass in contact with hardened cement paste (HCP) were performed to assess its behavior under simulated repository conditions. Batch experiments were conducted at 20 °C and 50 °C in several artificial cement pore water (ACW) samples (pH from 10 to 13), in the presence of HCP (CEM-I, CEM-V and low pH), with a ratio of glass surface to volume of solution of 8000 m−1 and a ratio of mass of HCP to volume of solution of 10 g L−1. Glass alteration rates increase up to ∼4 × 10−2 g m−2 d−1 with pH in contact with HCP, notably with CEM-I. This value decreases by 2 orders of magnitude in low pH cement solution and also for residual alteration rates. The effect of calcium on glass alteration was observed, mainly in Ca(OH)2 saturated solution, with an incubation effect on the release of Si in solution. Experimental data were successfully modeled with the PhreeqC geochemical code. Glass and HCP samples were characterized via SEM/EDX and micro-Raman studies. This work showed that vitrified glass exhibits good performance in terms of low alteration rates (∼10−4 g m−2 d−1), the absence of secondary phases, and the formation of a gel layer at the surface, when in contact with low pH conditions (in the presence or absence of low pH HCP).

Since the ability to provide lattice oxygen should be an important factor dictating the catalytic activity of supported gold catalysts, we synthesized, simply by oxidation of the primary AuCe, AuZr, AuCeZr alloys, intimate mixtures of nanostructured Au with CeO 2 , ZrO 2 or Ce–Zr mixed oxides which have unique redox properties and high mobility of lattice oxygen. This makes it possible to accurately study the influence of the support identity on the catalytic activity. A detailed investigation of the preferential oxidation of CO (PrOx) in the presence of H 2 was undertaken also with the oxidation of CO and the oxidation of H 2 . For CO oxidation, it immediately appears that the nature of the oxide affects significantly the activity of gold, ceria being the best whereas for H 2 oxidation no or only slight support effect has been observed. Catalytic performances in the PROX reaction were compared with those in the oxidation of CO. A change in the conversion of CO was observed in the presence of H 2 at low temperature for all system, the effect depending on the support identity. A boost is clearly observed on Au/ZrO 2 whereas the samples containing ceria present an opposite effect: when H 2 is introduced in the reactive mixture, the CO conversion rate is drastically decreased. According to a Mars–van Krevelen mechanism, implying lattice oxygens of the cerium oxide it was suggested that the presence of H atoms in the vicinity of gold should reduce considerably the oxygen spillover activity. At higher temperature, hydrogen can desorb from ceria and the opposite trend is observed. Whereas the rate of CO’s oxidation decreases in a regular and fast way with the temperature for AuZr, it decreases more slowly when ceria is present. This could explain the better selectivity obtained with ceria containing gold catalysts as compared to gold–zirconia material in the high temperature range. Indeed when H 2 is no longer present on the support, oxygen spillover activity should be recovered and CO oxidation favored. In any case we showed that Au/CeO 2 , in our conditions, is not active in the WGS reaction.

We investigated the role of temperature on the carbon steel corrosion under simulated geological conditions. To simulate the effect of temperature increase due to radioactive decay, we conducted batch experiments using Callovo-Oxfordian (COx) claystone and synthetic water formation with steel coupons at 30 °C and 90 °C for 6 months. The corrosion products have been studied by scanning electron microscope/energy dispersive X-ray spectroscopy, X-ray diffraction and micro-Raman spectroscopy. At 30 °C, experiments showed the formation of magnetite and iron sulphide, indicating the activation of sulphate-reducing bacteria. At 90 °C a continuous iron sulphide layer was identified on steel surface due to the reduction by hydrogen of pyrite originating from claystone into pyrrhotite and hydrogen sulphide. Thus, sulphide production may occur even in the absence of microbial activity at high temperature and must be taken into consideration regarding the near-field geochemical evolution.

During the geological disposal of high-level waste, the nuclear glass is expected to be first hydrated in water vapor prior to liquid alteration. In the present work, we investigated the vapor hydration of the International simple glass (ISG) at 175°C and different relative humidities (60%, 80% and 98%). The glass hydration was investigated by nuclear reaction analysis (NRA) and Fourier transform infra-red spectroscopy. The chemical and mineralogical compositions of the alteration products were studied using scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS) and l-Raman spectroscopy, respectively. The NRA results gave water diffusion coefficients of 2.31–7.34 9 10 � 21 m 2 /s, in good agreement with the literature data on borosilicate glasses altered in aqueous media. The glass hydration increased with relative humidity percentage and the SEM-EDS analysis showed a slight enrichment in Si and loss of Na in the hydrated glass layer compared with the pristine glass. The hydration rate of the ISG glass was little higher than that of the French SON68 glass hydrated using water vapor. The corrosion products were analcime, tobermorite, and calcite, which were typical of the SON68 glass hydrated in similar conditions.

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International audience; The intimate mixture of a skeletal gold structure with ZrO2 nanoparticles obtained simply by oxidation of Au0.5Zr0.5 alloy at room temperature turns out to be an efficient catalyst for the selective oxidation of CO in the presence of hydrogen.