Impact of a 70°C temperature on an ordinary Portland cement paste/claystone interface: An in situ experiment

International audienceRadioactive wastes in future underground disposal sites will induce a temperature increase at the interface between the cementitious materials and the host rock. To understand the evolution of Portland cement in this environment, an in situ specific device was developed in the Underground Research Laboratory in Tournemire (France). OPC cement paste was put into contact with clayey rock under water-saturated conditions at 70°C. The initial temperature increase led to ettringite dissolution and siliceous katoite precipitation, without monosulfoaluminate formation. After one year of interaction, partial decalcification and diffuse carbonation (calcite precipitation) was observed over 800 μm in the cement paste. At the interface, a layer constituted of phillipsite (zeolite), tobermorite (well-crystallised C-S-H), and C-(A)-S-H had formed. Globally, porosity decreased at both sides of the interface. Geochemical modelling supports the experimental results, especially the coexistence of tobermorite and phillipsite at 70°C, minerals never observed before in concrete/clay interface experiments

UMAN – a pluralistic view of uncertainty management

Decisions associated with Radioactive Waste (RW) Management programmes are made in the presence of irreducible and reducible uncertainties. Responsibilities and roles of each actor, the nature of the RW disposal programme and the stage in its implementation influence the preferences of each category of actors in approaching uncertainty management. UMAN (UMAN – Uncertainties Management Multi-Actor Network is a Work Package of the European Radioactive Waste Management Programme – EURAD) carries out a strategic study about the management of uncertainties based on extended exchanges among actors representing Waste Management Organisations, Technical Support Organisations, Research Entities and Civil Society, a review of knowledge generated by past and ongoing R&D projects, and findings of international organisations. UMAN discusses the classification schemes and approaches applied in uncertainty management, and identifies possible actions to be considered in the uncertainty treatment. The relevance for the safety of the uncertainties associated with waste inventory, including spent fuel, near-field, site and geosphere and human aspects, as perceived by each type of actors, and approaches used in their management are explored with the aim to reach either a common understanding on how uncertainties relate to risk and safety and how to deal with them along the programme implementation, or at least arrive at a mutual understanding of each individual view. Finally, uncertainties assessed as highly significant and the associated R&D issues that can be further investigated are being identified

Experimental and kinetic modeling study of benzene and toluene combustion in premixed, laminar and one-dimensional flames

Flames that have an excess of fuel, compared to the stoichiometry, or where the mixing between fuel and oxidizer is imperfect, result in an incomplete combustion. The excess of fuel is principally converted into Polycyclic Aromatic Hydrocarbons (PAH), which are molecular precursors of soot. In addition to the carcinogenic hazard of PAH, soot promotes the atmospheric solar heating or causes the coating of combustion chambers in the industry. It is therefore very important to understand mechanisms involved in the chemistry of soot formation. Such a comprehension is the main goal of this work investigating chemical pathways involved in benzene and toluene flames. One-dimensional, premixed and laminar benzene-oxygen-argon and toluene-oxygen-argon flames have been stabilized at different equivalence ratios and at low pressure on a flat flame burner. Experimental structures have been determined by Gas Chromatography, enabling the detection of major products of combustion, small hydrocarbon intermediates and chemical species from C6Hx to first PAH. Molecular Beam Mass Spectrometry has been used to detect chemical species of interest that could not be followed by Gas Chromatography. These species include the phenoxy radical, the benzoquinone, the benzyl radical and the fulvenallene, which are all thought to be important intermediates of benzene and toluene combustion. Finally, a device has been developed for the measurement of soot concentration in rich hydrocarbon flames. A detailed kinetic model for the aromatic consumption and the soot formation has been developed on the basis of a comprehensive literature survey. The good predictive capability of the proposed model has been verified by comparing its predictions to the experimental flame structures. Comparative reaction rate analyses have been carried out to determine the main reaction pathways occurring in aromatic flames. The comprehensive experimental and kinetic modeling studies presented in this work improve the current understanding of aromatic flame chemistry, and will help the future works devoted to aromatic oxidation, as well as those on PAH and soot formation.(CHIM 3) -- UCL, 201

Experimental and kinetic modeling investigation of toluene combustion in premixed, one-dimensional and laminar toluene-oxygen-argon flames

One-dimensional, premixed and laminar toluene-oxygen-argon flames, with equivalence ratios of 0.7 and 1.0 were stabilized at low pressure on a flat flame burner. Mole fraction profiles of 18 chemical species have been measured by gas chromatography and molecular beam mass spectrometry. A kinetic model with a good predictive capability has been developed to compare with experimental data. A comparative reaction rate analysis of predicted flame structures has allowed us to determine main pathways of toluene combustion and their dependence on temperature and equivalence ratio. © 2010 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved

Experimental and kinetic modeling evidences of a C7H6 pathway in a rich toluene flame.

The structure of a laminar, premixed, and one-dimensional toluene-oxygen-argon (9.9 mol % C(7)H(8), 44.5 mol % O(2), and 45.6 mol % Ar) flame, with an equivalence ratio of 2 and burning at 36 Torr was analyzed by gas chromatography and molecular beam mass spectrometry (MBMS). Mole fraction profiles of 25 chemical species including permanent gases of combustion and first polycyclic aromatic hydrocarbons as naphthalene, methylnaphthalene isomers, biphenyl, and phenanthrene have been measured. A kinetic model based on recent literature data has been elaborated to compare with measurements. As suggested by recent theoretical studies, benzyl radical (C(7)H(7)) dissociation into fulvenallene (C(7)H(6)) + H and the reaction between C(7)H(6) and H giving cyclopentadienyl radical and acetylene have been included into the model. A comparison between experimental and predicted flame structures have allowed us to validate the kinetic model for rich toluene combustion. Moreover, MBMS measurements of mole fraction profiles corresponding to m/z ratios of C(7)H(7) and C(7)H(6) have permitted a specific validation of the theoretically postulated C(7)H(6) pathway in toluene flames

Molecular Beam Mass Spectrometry analysis of PAH production pathways in C6H6/O-2/Ar and C6H6/C2H2/O-2/Ar flames

One-dimensional benzene-oxygen-argon (11.5mol% C6H6, 43.2mol% O-2 and 45.3mol% Ar) and benzene- acetylene- oxygen- argon (10.7mol % C6H6, 2.6mol % C2H2, 43.2mol % O-2 and 43.5mol% Ar) flames with an equivalence ratio of 2 were stabilized at low pressure (45 mbar) on a flat flame burner. Gas sampling was achieved by a conical quartz nozzle, at different positions of the flame. Identification and monitoring of chemical species was performed by Molecular Beam Mass Spectrometry (MBMS). Every chemical species was analyzed in both flames, under similar conditions, in order to perform a reliable calibration and a direct comparison. Experimental results and their comparison to simulated data provide interesting clues to evaluate more precisely the role of acetylene in hydrocarbon and PAH production

Experimental study and kinetic modeling of benzene oxidation in one-dimensional laminar premixed low-pressure flames

One-dimensional laminar premixed benzene-oxygen-argon flames with equivalence ratios of 2, 1, and 0.7, stabilized at low pressure (45 mbar) on a flat flame burner are studied. Gas sampling is performed by a conical quartz nozzle, at different positions in the flames. Identification and monitoring of chemical species is performed by gas chromatography. These measurements should complete experimental data on rich and sooting benzene flames available in the literature and will be of particular help for further improvements of benzene oxidation mechanisms. A comparison of experimental results with data simulated with the use of two recent kinetic models highlights their inability to predict stoichiometric and lean benzene combustion

Modelling of temperature impacts on cement paste in clayey environment constrained by field experiments

International audienc

Implications of safety requirements for the treatment of THMC processes in geological disposal systems for radioactive waste

The mission of nuclear safety authorities in national radioactive waste disposal programmes is to ensure that people and the environment are protected against the hazards of ionising radiations emitted by the waste. It implies the establishment of safety requirements and the oversight of the activities of the waste management organisation in charge of implementing the programme. In Belgium, the safety requirements for geological disposal rest on the following principles: defence-in-depth, demonstrability and the radiation protection principles elaborated by the International Commission on Radiological Protection (ICRP). Applying these principles requires notably an appropriate identification and characterisation of the processes upon which the safety functions fulfilled by the disposal system rely and of the processes that may affect the system performance. Therefore, research and development (R&D) on safety-relevant thermo-hydro-mechanical-chemical (THMC) issues is important to build confidence in the safety assessment. This paper points out the key THMC processes that might influence radionuclide transport in a disposal system and its surrounding environment, considering the dynamic nature of these processes. Their nature and significance are expected to change according to prevailing internal and external conditions, which evolve from the repository construction phase to the whole heating–cooling cycle of decaying waste after closure. As these processes have a potential impact on safety, it is essential to identify and to understand them properly when developing a disposal concept to ensure compliance with relevant safety requirements. In particular, the investigation of THMC processes is needed to manage uncertainties. This includes the identification and characterisation of uncertainties as well as for the understanding of their safety-relevance. R&D may also be necessary to reduce uncertainties of which the magnitude does not allow demonstrating the safety of the disposal system

Geochemical evolution of cementitious materials in contact with a clayey rock at 70 C in the Tournemire underground research laboratory

International audienc