[en] We propose an elasto-plastic model coupled with damage for the behavior of geomaterials in compression. The model is based on the properties, shown in S. Andrieux, et al., 'Un modele de materiau microfissure pour les betons et les roches', J. Mecanique Theorique Appliquee 5 (1986) 471-513, of microcracked materials when the microcracks are closed with a friction between their lips. That leads to a macroscopic model coupling damage and plasticity where the plasticity yield criterion is of the Drucker-Prager type with kinematical hardening. Adopting an associative flow rule for the plasticity and a standard energetic criterion for damage, the properties of such a model are illustrated in a triaxial test with a fixed confining pressure. (authors)

[en] Sustainability is one of the challenging issues in electricity production systems. Recently, solid oxide fuel cell (SOFC) has been suggested for use in combined heat and power (CHP) systems. This application is introduced as a promising environmentally-friendly system according to the thermodynamic and electrochemical models. In this paper, an atmospheric SOFC/CHP cycle was analysed based on integrating exergy concepts, energy and mass balance equations. In this regard, a zero-dimensional energy and mass balance model was developed in engineering equation solver (EES) software. Two dimensionless parameters (the exergetic performance coefficient (EPC) for investigating the whole cycle, and exergetic efficiency for investigating the exergy efficiency of the main component of this cycle) were applied. Results show that efficiencies of the system have been increased substantially. The electrical efficiency, total efficiency and EPC of this cycle were ∼54%, ∼79% and ∼58% respectively. Moreover, the CO₂ emission is 19% lower than when compared with a conventional combined power cycle fed by natural gas. In addition, a dynamic economic evaluation was performed to extract the most sensitive parameters affecting the outputs: electricity sales price (ESP), equipment purchase cost and fuel cost. Furthermore, an electricity production cost of ∼125 $ MW.h^-1 was attributed to our model, resulting in yet further cost reduction for widespread applications of this cycle. (authors)

[en] Particle trapping and deposition around an obstacle occur in many natural and industrial situations and in particular in the nuclear industry. In the steam generator of a nuclear power plant, the progressive obstruction of the flow due to particle deposition reduces the efficiency and can induce tube cracking leading to breaking and damage. The steam generator then loses its role as a safety barrier of the nuclear power plant. From a fundamental standpoint, dilute and concentrated particulate flows have received a growing attention in the last decade. In this study, we investigate the transport of solid particles around obstacles in a confined flow. Experiments were performed in a simplified configuration by considering a laminar flow in a vertical tube. An obstacle was inserted at the middle height of the tube and neutrally-buoyant particles were injected at different locations along the tube. We have investigated first the trajectories of individual particles using particle tracking (PT). Then, the particle trajectories were modeled by using the Boussinesq-Basset-Oseen equation with a flow velocity field either measured using particle image velocimetry (PIV) or calculated by the Code-Saturne software in order to account for the three-dimensional (3D) character of the obstacle wake. This paper presents a comparison between the experimental observations and the predictions of the modeling for an obstacle consisting of a rectangular step at a Reynolds number of approximate to 100 and evidences the importance of accounting for the 3D complex nature of the flow. (author)

[en] The fuel handling operating rules exclude any accidental risk. However in the framework of the PRECCI R and D project, the bending of a spent fuel assembly resulting from its locking during a translation displacement is taken into account. This enabled us to develop an approach based on experiments and calculations that allows us to simulate the behaviour of an assembly under such loading. This study was carried out in CEA laboratories with the funding and the technical support of EDF. A three points bending test on a spent fuel rod segment was performed at the Laboratory for Mechanical Behaviour of Irradiated Materials (LCMI). From the experimental strength-displacement curve, a maximum failure strain, a maximum failure curvature and an equivalent constitutive equation were determined. CAST3M modelling of the fuel rod taking into account the elasto-plastic behaviour of the clad and the cracking of the UO₂ fuel pellets was verified by the experimental results. Consequently, the identification of the respective contributions of the clad and of the pellets to the rod global behaviour was made possible. A two dimensional assembly with beam elements was modelled with CAST3M. The properties of the beams modelling the different parts of the assembly (top and bottom nozzle, grids) were chosen and adjusted according to their materials (zirconium alloys, steel) in order to obtain stiffness, tensile and shear behaviour, sliding and holding functions close to the experimental ones. Assembly bending calculations were performed. In order to obtain a rod integrity estimator, their maximum calculated strains and curvatures as a function of the bending angles can be compared to the failure experimental ones. (authors)