Development of numerical methods for the reactive transport of chemical species in a porous media : a nonlinear conjugate gradient method

In the framework of the evaluation of nuclear waste disposal safety, the French Atomic Energy Commission (CEA) is interested in modelling the reactive transport in porous media. At a given time step, the equation system of reactive-transport can be written as a system of nonlinear coupled equations F(x) = 0. In the computational code which is presently used, this system is solved using classical sequential iterative algorithms (SIA). We are currently investigating nonlinear conjugate gradient methods to improve the resolution of the system. Indeed, the handling of the coupling is improved by numerical derivation along the descent direction. The original feature of this method is the use of an explicit formula for the descent parameter. We choose an approach involving two distinct codes, that is one code for the chemistry and one code for the transport equations

Development of numerical methods for the reactive transport of chemical species in a porous media : a nonlinear conjugate gradient method

In the framework of the evaluation of nuclear waste disposal safety, the French Atomic Energy Commission (CEA) is interested in modelling the reactive transport in porous media. At a given time step, the equation system of reactive-transport can be written as a system of nonlinear coupled equations F(x) = 0. In the computational code which is presently used, this system is solved using classical sequential iterative algorithms (SIA). We are currently investigating nonlinear conjugate gradient methods to improve the resolution of the system. Indeed, the handling of the coupling is improved by numerical derivation along the descent direction. The original feature of this method is the use of an explicit formula for the descent parameter. We choose an approach involving two distinct codes, that is one code for the chemistry and one code for the transport equations

Coupling Methodology within the Software Platform Alliances

CEA, ANDRA and EDF are jointly developing the software platform ALLIANCES which aim is to produce a tool for the simulation of nuclear waste storage and disposal repository. This type of simulations deals with highly coupled thermo-hydro-mechanical and chemical (T-H-M-C) processes. A key objective of Alliances is to give the capability for coupling algorithms development between existing codes. The aim of this paper is to present coupling methodology use in the context of this software platform.Comment: 7 page

Analyse asymptotique des équations de dérive-diffusion et équations de Hamilton-Jacobi

Projet M3NNous étudions le comportement asymptotique des équations de dérive-diffusion (DD) des semi-conducteurs. Pour cela, après un changement d'échelle, nous faisons apparaître un petit paramètre $\lambda$ devant le terme de diffusion. Pour obtenir un problème limite complet, nous devons introduire deux fonctions liées au logarithme de la concentration des électrons. Nous montrons, qu'avec ces nouvelles variables, le problème limite s'exprime sous la forme d'un système couplé équations de Hamilton-Jacobi - inéquations variationnelles. Dans le cas unidimensionnel, nous prouvons l'unicité de ce problème limite~; cela nous donne alors toutes les informations nécessaires pour étudier le comportement du modèle DD pour $\lambda$ petit. Nous étudions aussi l'intérêt de ces nouvelles variables au niveau numérique. Notre méthode étend les résultats connus, précise également la convergence de la concentration des électrons, améliore les hypothèses nécessaires et enfin donne une approche originale au problème susceptible d'être utilisée au niveau numérique

Analyse de sensibilité et estimation de paramètres de transport pour une équation de diffusion, approche par état adjoint

L'identification des coefficients d'une équation aux dérivées partielles (EDP) entre dans le cadre des problèmes inverses. L'analyse de la sensibilité des mesures de la solution de l'EDP par rapport aux coefficients à estimer est alors une technique efficace d'aide à la résolution du problème. En quantifiant le nombre de degrés de liberté identifiables de fa on stable, elle permet de guider le choix d'une paramétrisation des coefficients de l'EDP adaptée au problème, mais également de tester des dispositifs de mesure plus performants pour l'inversion. Dans ce travail, l'EDP est une équation de diffusion en milieu poreux. Des outils efficaces tels la décomposition en valeurs singulières, pour l'analyse de sensibilité, et la méthode de l'état adjoint, pour le calcul des dérivées, sont mis en oeuvre

Intercomparison of reactive transport models applied to UO2 oxidative dissolution and uranium migration

International audienceOxidative dissolution of uranium dioxide (UO2) and the subsequent migration of uranium in a subsurface environment and an underground waste disposal have been simulated with reactive transport models. In these systems, hydrogeological and chemical processes are closely entangledand their interdependency has been analyzed in detail, notably with respect to redox reactions, kinetics of mineralogical evolution and hydrodynamic migration of species of interest. Different codes, where among CASTEM, CHEMTRAP and HYTEC, have been used as an intercomparison and verification exercise. Although the agreement between codes is satisfactory, it is shown that the discretization method of the transport equation (i.e. finite elements (FE) versus mixed-hybrid FE and finite differences) and the sequential coupling scheme may lead to systematic discrepancies

Strategies for solving index one DAE with non-negative constraints: Application to liquid-liquid extraction

18 pagesInternational audienceLiquid-liquid extraction modeling leads to solve an index one DAE system. For the sake of robustness, it is desirable to account for non-negative constraints. Based on the DASSL architecture (a classical index one DAE solver) we propose and compare three different strategies to implement these bound constraints. Each of these strategies corresponds to a different Newton modification: clipping, damping, or interior point method. The comparisons are made on two test cases: the Robertson ODE problem, and an example from liquid-liquid extraction modeling

Presentation on Multi-Phase CFD Solver Neptune_CFD

The NEPTUNE project constitutes the thermal-hydraulic part of the lon, g term EDF-CEA-AREVA-IRSN joint research and development program for the next genration of nuclear reactor simulation tools. The project aims at developing high modeling capabilities for advanced two-phase flow thermal-hydraulics covering the whole range of modeling scales. The CFD scale for flow description is covered with NEPTUNE_ CFD code. The multiphase approach, developed at EDF in the NEPTUNE_ CFD code for nuclear engineering, is based on separate Eulerian transport equations for mass, momentum, energy and turbulent quantities of the different fluids, which are coupled through inter-phase transfer terms. This model is primarily dedicated to the simulation of multiphase flows containing one continuous fluid always present, wohich carries dispersed fluids present in the form of bubbles, droplets, particles, whose dimension are much smaller than the spatial resolution length of the model. The simulation of all range of multiphase flow situation, sauch as dispersed and liuid/ gas stratified (separated) flows, which can be encountered in nuclear PWR circuits and pipes under nominal or incidental conditions, remain challenging cases for multiphase volume averaged flow models. The paper deals with a short presentation of NEPTUNE_ CFD model, dedicated to incompressible, weakly compressible, unsteady and turbulent 3D two phase flow computations. Some modeling strategies will be detailed through the examples of two validations of semi-integral cases.Mechitoua Namane, Guingo Mathieu, Montarnal Philippe. Presentation on Multi-Phase CFD Solver Neptune_CFD. In: SimHydro 2014. New Trends in Simulation. 11-13 June 2014 Ecole Polytech’ Nice (France) 2014

Impact of spatial heterogeneities on oxygen consumption in sediments: Experimental observations and 2D numerical modeling

International audienc