H2 gas production in calcium silicate hydrates: influence of water content and radiation induced defects

International audienceWater radiolysis is a major concern for the conditioning of radioactive waste in cement materials. Synthetic calcium silicate hydrate (CSH), the main hydrates of concrete, were synthesized with different C/S ratios and relative humidities. The samples were irradiated under γ- and electron beam irradiation. The radiolytic hydrogen production has been quantified and the radiation induced defect produced at low temperature characterized by electron paramagnetic resonance. The results show that the H production and defect production are only marginally sensitive to the relative humidit

Water content and porosity effect on hydrogen radiolytic yields of geopolymers

International audienc

Water content and porosity effect on hydrogen radiolytic yields of geopolymers

International audienc

Water content and porosity effect on hydrogen radiolytic yields of geopolymers

International audienc

Complexing power of hydro-soluble degradation products from γ\gamma-irradiated polyvinylchloride: influence on Eu(OH)3_3(s) solubility and Eu(III) speciation in neutral to alkaline environment

International audienceThe complexing power of hydrosoluble degradation products (HDPs) from an alkaline hydrolysis of a 10 MGy $\gamma$-irradiated polyvinylchloride is studied. The complexation of Eu(III), as an analogue of lanthanide and actinide radionuclides at their + III oxidation state for oxygen containing functions, is evidenced both from the increasing of Eu(OH)$_3$(s) dissolution, and from a complexometric titration by time-resolved luminescence spectroscopy. The dissolution of Eu(OH)$_3$(s) in a simplified alkaline solution (0.3 M KOH/0.1 M NaOH) increases moderately, but significantly, with the HDPs concentration. The luminescence signal of the supernatant clearly indicates the presence of several complexed Eu(III) species. Performing a complexometric titration of Eu(III) from pH 6 by alkaline HDPs shows the formation of two different species with increasing HDPs' concentration and pH. Operational complexation constants - based on dissolved carbon concentration - are proposed. The analyses of the spectra and luminescence decays seem to confirm the presence of two different species

Alkaline hydrolysis of radio-oxidized aliphatic polymers

International audienceTo ensure the safety of the French deep geological repository, the degradation of organic molecules which can be found in long-lived intermediate-level waste (LL-ILW) packages has to be very well understood. In a first period, these molecules which include polymers are radio-oxidized because they are in contact with radionuclides. In a second period, water will diffuse inside the site to the packages and radio-oxidized polymers will suffer alkaline hydrolysis. The objective of this article is to evaluate the parameters of influence when polyolefins suffer leaching at high pH; aliphatic polymers being chosen because of their relative importance, in quantity, in the LL-ILW packages. In this work, we have evaluated the influence of the materials’ composition (nature of the resin, presence of charges and fillers) and of the irradiation conditions (nature of the irradiation, linear energy transfer LET and dose). We observed that degradation is influenced by the molecular structure of the polymer, but also by the presence of inorganic fillers and organic charges. Degradation of the materials under study increases with dose and LET (in the case of comparison between ions irradiations), the most penalizing conditions being encountered using low LET ionizing rays compared to swift heavy ions irradiation. We observe that the higher the oxidation rate, the higher the polyolefins sensitivity to alkaline hydrolysis

Effect of gamma irradiation on MnO2/Ag2O hydrogen getter

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Influence of the cement composition on the radiolytic behavior under irradiation

International audienceCement based materials are used for the conditioning of Low and Intermediate Level Wastes (LILW)due to their low cost, their ease of making and their ability to immobilize radioelements. Nevertheless,hydrogen gas is produced radiolytically under irradiation. For the safety of nuclear waste disposals, itis important to limit as much as possible the hydrogen gas release.A comparison of the behavior of Portland and Ciment Fondu® cements under irradiation taking intoaccount both real cement pastes and synthetic hydrates was performed to find out the role of the cementcomposition on the radiolytic behavior under irradiation. First, γ-irradiations were performed usinga 60Co source (dose rate: 0.17 - 0.25 Gy.s-1, dose: up to 500×103 Gy). Thermogravimetric analysismeasurements were performed in order to determine the amount and the type of water involved. H2gas production was measured by gas chromatography. Regardless of the water to cement ratio (W/C)chosen (0.2, 0.4 and 0.6), it is shown that Ciment Fondu® pastes produce less H2 under irradiation. Inagreement with a recent study by Kadissy et al. [1], it is shown that the amount of gas produced byportlandite and gibbsite, which are respectively the constitutive hydrates of Portland and Ciment Fondu® cements, strongly depends on the nature of the hydrate. Secondly, portlandite and gibbsite wereirradiated by electrons up to 270 MGy and 3.5 GGy using the LSI SIRIUS accelerator platform. X-RayDiffraction analyses were performed before and after irradiation in order to investigate the structuraldamage. Despite some observed disorder, results show a good structural stability for both hydratesunder irradiation

H2 production under gamma irradiation of a calcium aluminate cement: an experimental study on both cement pastes and its stable hydrates

International audienceThe objective of this paper is to investigate the use of calcium aluminate cements as alternative cements within the context of nuclear waste stabilization by solidification. Using an external 60 Co source, the effect of γ-radiation on H2 gas production of one of the calcium aluminate cement-based materials (cement "Ciment Fondu") and its stable hydrates, was studied. The amount of H2 produced by these cement pastes is found to be much lower (up to five times less) than that of the Portland cement pastes containing the same amount of water, especially in the low range of water to cement ratios (W/C ≤ 0.4) where water is essentially engaged in the hydrates. The H2 production of the two major hydrates of Ciment Fondu, gibbsite AH3 and katoite hydrogarnet C3AH6, is very low compared with that of the main hydrates of other cements (Portland cement, Calcium Sulfo-Aluminate and Magnesium Phosphate cements). The type of water engaged in the hydrates, as hydroxyl groups and/or molecular water, influences significantly the H2 production. Thus, the nature of the hydrate is a key parameter to the aim of optimizing cement matrices with respect to the gas production under irradiation. XRD analysis shows that the crystal structures of gibbsite and katoite are preserved up to very high doses under electron irradiation (3 GGy). This makes calcium aluminate cements (CAC) potential good candidates for nuclear waste conditioning from the point of view of their stability under irradiation