Investigating chemical and cracking processes in cement paste exposed to a low external sulfate attack with emphasis on the contribution of gypsum

International audienceDurability of concrete exposed to an external sulfate attack is a great concern for the long-term reliability of nuclear waste containment. This paper presents experimental results obtained on cement paste subjected to a low concentration (30×10-3 mol/L) external sulfate attack. Samples were characterized with complementary methods (XRD, SEM-EDS, microtomography, microindentation, autoradiography) to follow the evolution of chemical, mineralogical, microstructural and mechanical properties during 8 months. Cement pastes of different C3A contents were used to boost either ettringite or gypsum formation during the sulfate attack to assess their respective impact on the degradation. Cracks parallel to the attacked surface occurred in the zone of gypsum formation and portlandite dissolution, which suggests that gypsum has a key effect on the expansion. Reactive transport modeling supported the discussion on the competition between hydrolysis, gypsum and ettringite precipitation as well as the analytical homogenization to estimate Young’s moduli

Effect of operating conditions on the retention of ruthenium tetroxide (RuO4) by different solid traps

International audienceMitigation of gaseous RuO4 is an important issue in nuclear safety in order to reduce potential radiological consequences, either in the context of severe accident arising on pressurized water reactors (oxidizing conditions) or in reprocessing plants (loss of cooling of fission product storage tanks). For the first time, RuO4 trapping was compared using three kinds of materials acting as solid traps: a functionalized MOF UiO-66-NH2, an amine-modified silica and a commercial cerium dioxide. Different experimental conditions of temperature, humidity and gas composition were investigated in order to mimic those prevailing under accident conditions at filtered containment venting system (FCVS) level or in ventilation ducts (gas mixture). At 50 °C, the efficiency of UiO-66-NH2 for RuO4 trapping was both very high in dry gas and in presence of steam with decontamination factor (DF) in the range 10 4-10 5. Under more severe conditions, the retention performances slightly decrease, especially when NO2 was present in the feed gas due to some poisoning of adsorption sites. In presence of amino-modified silica, breakthrough of RuO4(g) occurred at an earlier stage due to its inferior adsorption capacity but the performances of the trap did not deteriorate in presence of steam and NO2 in gas mixture. Under similar conditions, cerium dioxide showed no retention of RuO4(g)

Optimal physical experimental designs to calibrate functional Weibull models under cost constraints. Application to a structural reliability problem

International audienceWe focus on the specific issue of identifying (static) optimal physical experimental designs when the aim is to calibrate functional Weibull models in an informed context and under cost constraints. In this nonlinear parametric context, a major difficulty is that the exact evaluation of the expected utility function to maximize is intractable. Among the proposed approaches to overcome this difficulty, one can distinguish near optimal Bayesian experimental designs defined by maximizing either an analytical approximation or a numerical estimation of the expected utility. These latest approaches are based on quadratic techniques or simulations produced by stochastic algorithms. They remain computationally intensive, which makes them often limited in practice to very simple designs. In this work, we explore the potential of the Bayesian approach to account for legacy data as a prior informative sample when designing physical experiments. We propose generic design criteria based on a weighted combination of utility functions to balance the statistical gain yielded by a given design and the prospective experimental cost, in an understandable way for the engineer. We consider different utility functions to quantify the statistical gain yielded by a given design when fitting Bayesian functional Weibull models. Finally, we derive analytical asymptotic approximations of the associated expected utility functions that we maximize with a simulated annealing algorithm. Our method is applied to a structural reliability problem informed by a real dataset of U.S. ferric steels. The design problem consists in selecting an optimal number of temperature levels, optimal values of temperature levels and optimal numbers of Charpy destructive impact tests to allocate to each temperature level, in order to produce the most precise estimates of the parameters defining the functional Weibull distribution of steel fracture toughness for a French production park under cost constraints

Development of a 14C protocol at the LMC14 for the dating of cultural heritage materials: Historial mortars. Participation in the MODIS international intercomparison campaign

International audienceABSTRACT The absolute dating of mortar by accelerator mass spectrometry (AMS) has been the subject of renewed interest for several years. International intercomparison campaigns, called MODIS (MOrtar Dating Intercomparison Study), have been carried out. The first MODIS-1 campaign highlighted limitations in mortar dating, due to the similarity between the primary material to be dated (binder) and the contaminant (exogenous CaCO 3 ). Methods have since emerged to overcome this problem and the need for a good preliminary characterization has been proven. The Laboratoire de Mesure du Carbone 14 (LMC14) took part in the second intercomparison campaign, MODIS2, by applying thermal decomposition increments to distinguish the carbonated binder, the organic matter contaminants (late in formation pyrogenic carbonate, LDH) and limestone. The LMC14 results on MODIS2 are quite conclusive on “pure” re-carbonated lime mortar binders containing little contaminant geological limestone but show their weaknesses for mortars heavily contaminated in Dolomites, which are difficult to discern from the binder. Recommendations for users of radiocarbon ( 14 C) dating on mortar-based materials are made in the conclusion

Directional detection of keV proton and carbon recoils with MIMAC

International audienceDirectional detection is the dedicated strategy to demonstrate that DM-like signals measured by direct detectors are indeed produced by DM particles from the galactic halo. The experimental challenge of measuring the direction of DM-induced nuclear recoils with (sub-)millimeter tracks has limited, so far, the maximal directional reach to DM masses around $100~\rm{GeV}$. In this paper, we expose the MIMAC detector to three different neutron fields and we develop a method to reconstruct the direction of the neutron-induced nuclear recoils. We measure an angular resolution better than $16^\circ$ for proton recoils down to a kinetic energy of $4~\rm{keV}$ and for carbon recoils down to a kinetic energy of $5.5~\rm{keV}$. For the first time, a detector achieves the directional measurement of proton and carbon recoils with kinetic energies in the keV range without any restriction on the direction of the incoming particle. This work demonstrates that directional detection is around the corner for probing DM with masses down to $\mathcal{O}(1~\rm{GeV})$

A toxicokinetic–toxicodynamic model with a transgenerational damage to explain toxicity changes over generations (in Daphnia magna exposed to depleted uranium).

International audienceWe used a toxicokinetic–toxicodynamic (TKTD) model to analyze chronic effects, in Daphnia magna exposed to waterborne depleted uranium (DU) for two or three successive generations (F0, F1 and F2). Our aim was to understand how DU toxicity for growth and reproduction increased across generations. For the first time in a TKTD model, we introduced a novel transgenerational damage compartment, whose level was transmitted from parents to progeny upon egg deposition. Various exposure regimes took account of differences in exposure among generations. We used a simplified dynamic energy budget applied to toxicology (DEBtox) including two independent physiological modes of action (pMoA). The first pMoA, a reduction in assimilation linked to internal concentration, was previously confirmed by complementary analyses (direct measurements of carbon assimilation, histological observations of gut epithelium alterations). The second pMoA, an increase in costs for growth and maturation linked to transgenerational damage, was the most likely among three possible pMoA affecting both growth and reproduction. Modelling results showed that internal concentration and transgenerational damage followed strongly different kinetics across generations, suggesting that the two pMoA played very contrasting roles in long-term DU toxicity for D. magna. Internal concentration only increased between generations F0 and F1, showing no further difference between generations F1 and F2. Our model was able to correctly describe and predict DU toxicity data, in all tested generations and concentrations, and provided a mechanistic explanation for the increase in DU toxicity across generations

Comprehensive framework for overcoming scientific challenges related to assessing radioactive ultra-fine (nano/micro) particles transfer at the atmosphere-leaf interface

International audienceFood products are prone into contamination after a nuclear emission of radionuclides. While the mechanisms of emission and deposition of ultrafine radioactive particles are well documented, the transfer of these species from the atmosphere into plants is poorly assessed. This is evident in the lack of quantification of particles distributed within plants, especially regarding particles physical-chemical criteria to plant of different properties. Such knowledge gaps raise the concern about the representativeness of risk assessment tools designed for the transfer evaluation of ionic/soluble species to be qualified for simulating insoluble species exposure and proposes a possible underestimation. This highlights the possible need for special particle codes development to be implemented in models for future emissions. In addition, the later tools utilize transfer factors aggregating relevant sub-processes, suggesting another weak point in their overall reliability. As researchers specialized in the nuclear safety and protection, we intend in this perspective, to develop a compressive analysis of the interaction of ultrafine particles with plants of different specificities at different level processes starting from particles retention and gradual translocation to sink organs. This analysis is leveraged in providing insights for possible improvements in the current modeling tools for better real-life scenarios representation

A MODEL FOR FINELY, INTRICATE, RANDOM MULTIPHASE SYSTEMS

A multiphase system is said fine for a given scale of observation if its phases are scattered in a large number of individual space domains within a unit of volume corresponding to the observation scale. In the same way, the system is said fine with regard to time if, at a given point, phases alternate very often during the time unit corresponding to the observation time scale. In addition, when time and space distributions of the phases does not present repetitive or periodic patterns, the system is said a finely intricate one. Finally, if intricacy results of the random distributions both in time and space of the phase domains, such systems are defined as Finely Intricate Random Multiphase (FIRM) systems. Canopies are simple and common ordinary FIRM multiphase systems. In forests, the air flows through canopies where the leaves are a second phase. An important practical question is the airborne particle deposition rates by time and volume units (let us say a few minutes and a cubic meter) on several hundred leaves which are ruffled by coupling with the turbulent air flow. Let us assume that all the le local instantaneous quantities required for describing a FIRM system are available. Let us assume that they obey the basic law of physics, and then both balance equations for each phase and transfer equations for their exchanges are available. Assuming we are able to solve such a set of equations, we obtain the behaviour of the system. But, the solutions will be intractable and useless because the amount of data required to describe the local instantaneous values of these quantities will be so huge that it will prevents any one from deriving understandable information directly from them. Then, how to proceed? First, we retain the idea to write down the set of basic balance and transfer equations for the local and instantaneous quantities. Two, instead to handle directly this set, we modify it using weighting operators in such a way to obtain new balance equations for weighted quantities. The reason for such a procedure is the following. Local equations are defined only where and when a phase is present and we know that such space time domains can be highly variable for FIRM systems. On the contrary, balance equations for the weighted quantities are defined at any point and instant. They provide a way to describe the behavior of these systems. Here after, starting from the balance equations of the local and instantaneous quantities, the FIRM model development provides balance equations for global quantities which are valid everywhere at the scale of interest for applications. A following paper will provide applications of this model to forest canopy and sea

Homogenized descriptions for the elastoplastic response of polycrystalline solids with complex hardening laws: Application to neutron-irradiated bainitic steels

International audienceHomogenized descriptions are provided for polycrystalline solids deforming in accordance with certain crystal plasticity laws recently proposed for neutron-irradiated bainitic steels. These laws express intragranular plastic slip rates in terms of resolved shear stresses and key microstructural features, such as densities of forest dislocations and of solute clusters, for a wide range of deformation rates, temperatures, and radiation doses. The elastic domain is delimited by thresholds on the resolved stresses that depend on dislocation densities in an intricate manner, and the plastic hardening is described by evolution laws of the Mecking–Kocks type for the dislocation densities with plastic slip. However, thresholds also depend nonlinearly on the resolved stresses themselves. Full-field homogenized descriptions are generated with a Fast Fourier Transform algorithm implemented in the computer code CraFT, while mean-field homogenized descriptions are generated by means of a linear-comparison scheme based on a generalized-secant linearization of the crystal plasticity laws. Multiple ways of accounting for plastic hardening in the mean-field descriptions are explored. Sample results are reported in the form of uniaxial traction curves and concomitant dislocation density evolutions under different scenarios. Overall, the generalized-secant linearization is found to provide an appropriate compromise between precision and mathematical complexity to generate homogenized descriptions for the elastoplastic response of polycrystalline media governed by complex crystal plasticity laws

Forward and Backward Lagrangian Probability Density Properties

A basic relationship between forward and backward lagrangian probability density functions (pdfs.) is derived for any continuous medium if mass conservation is postulated. For an incompressible medium these pdfs are identical: see equation (45). This identity is used to generalize some previous results obtained under more restrictive hypotheses. It is shown:1.Identity of forward and backward variances for dispersion was established under the condition of unstrained stationary flow [1]. The same identity is obtained hereafter under homogeneity condition only.2.Identity of Eulerian and Lagrangian velocity moments was established under homogeneous and stationary flow conditions [2]. This identity and the equality of the lagrangian and eulerian velocity pdfs are established here for homogeneous and unsteady conditions.These results were published first year 1981 in French in the “comptes-rendus” of the French Science Academy [3]. Such an issue imposes a very concise paper limiting additional developments and explanations. We propose herewith such additions providing an opportunity for longer explanations of how such results are obtained.Chapter two is devoted to the description of deterministic random displacement of a continuous medium, e.g. a turbulent fluid flow. In addition, elementary elements of probability tools are provided in connection with the developments of the chapter three. This one addresses the question of forward and backward displacements and their respective lagrangian pdfs and proves their equality. Finally, chapter four establishes the results 1 and 2 mentioned above in this introduction using forward and backward pdfs. equality