Simulation of reactive gas-liquid multi-phase flows
The objective of this postdoctoral position is to develop and implement a simulation method for the simulation of a
sodium spray fire. Two key points need to be adressed. First, one needs to propose a proper representation of the sodium
droplets (dispersed phase) from their generation by a jet (separate phase) fragmentation to their behavior (motion,
oxidation, combustion) in the air atmosphere. This requires to derive a flow model that accounts for multiple components
with multiple interface topology regimes (dispersed and separate). Second, one needs to develop a robust discretization
strategy for this complex flow model.
The numerical work will be implemented in a new numerical tool to perform simulations of sodium spray fires developed at CEA. This tool is based on the canoP. Canop is a library designed for solving computational fluid dynamics problems using a cell-based
Adaptive Mesh Refinement (AMR) approach and parallel calculation.
Application of the Hybrid-High-Order (HHO) method for the treatment of non-local effects in crystal plasticity via a micromorph approach
Describing the behavior of materials at the crystalline scale is the subject of much academic research, and is of growing interest in industrial R&D studies. Classically, this description is based on behavior laws describing the local evolution of the material's microstructural state: (visco-)plastic deformation, dislocation density, etc.
The main driving force behind this evolution is resolved shear stress, the projection of the stress tensor on the slip systems.
The formalism of these local constitutive equations (as opposed to non-local constitutive
equations discussed hereafter) is now well established, whether we are considering
infinitesimal or finite transformations, and benefits from special support within the MFront code generator. Thanks to MFront, those constitutive equations can be used in various mechanical solvers at CEA (Manta, Cast3M , Europlexus , AMITEX_FFTP ) and EDF
(code_aster, Manta, Europlexus ).
However, the use of local constitutive equations does not allow to account for many effects.
The aim of the post-doc is to develop a robust numerical strategy for reliably solving
structural problems using non-local crystal plasticity laws, and guaranteeing the
transferability of the constitutive equations between the CEA and EDF codes.
Developement of a simulation platform for the energy systems
The evolution of power systems towards smart-grids, including a high share of renewable generation which can be combined with storage systems, lead to an increased complexity for designing and optimizing these systems. This leads to a need for new modeling and simulation tools, which have to manage different energy sources, different energy vectors and different technologies for energy conversion. Moreover, such simulation tools will be used to optimize the system sizing and to design energy management strategies.
The objective of this project is to design the software architecture for the simulation platform, which will be in ad equation to the previously mentioned needs. Such software will be organized in order to maximize the transfer towards industrial partners. The software will be able to support multi-energy systems, and will leave the possibility for the user to implement its own component models or energy management strategies.
The project is focused on the simulation platform architecture, and on the architecture model. This architecture will be used as a base for the development of a software. The objective of the given project is not to cover all the applications but rather to validate the architecture through a given application.
Development and characterization of concentrator photovoltaic (CPV) receivers for high-efficiency CPV modules
Concentrator photovoltaics (CPV) arises as a promising technology capable of economically justify the use of highly efficient (and highly expensive) monolithically stacked multijunction solar cells (MJSC). CPV takes advantage of low-cost optical elements, such as mirrors or lenses, to capture the sunlight and concentrate it into small-size cells, exchanging solar cell surface by optical elements. This technology, which is at an industrial stage, uses state-of-the-art triple junction (3J) solar cells with efficiencies up to 45%.
The postdoc position here proposed will deal with novel architectures of CPV receivers conceived from high-efficiency MJSC that will be integrated in next-generation CPV modules. The research engineer will also need to learn how to characterize these systems, for which he/she will use the tools available at the CPV Lab at INES (CEA). Novel characterization techniques may also be required.
The candidate must have a M.S. in Physics or Engineer with specialization on solid state physics, electronics, electrical engineering, mechatronics or similar. He/she must be a PhD, preferably in the field of photovoltaics and particularly on CPV. Good language skills and laboratory experience are required.
Robust path-following solvers for the simulation of reinforced concrete structures
Path-following procedures are generally employed for describing unstable structural responses characterized by ``snap-backs'' and/or ``snap-troughs''. In these formulations, the evolution of the external actions (forces/displacements) is updated throughout the deformation process to fulfill a given criterion. Adapting the external loading during the calculation to control the evolution of the material non-linearities is helpful to obtain a solution and/or to reduce the number of iterations to convergence. This second aspect is of paramount importance, especially for large calculations (at the structural scale). Different path-following formulations were proposed in the literature. Unfortunately, an objective criterion for choosing one formulation over another for the simulation of reinforced concrete (RC) structures (in the presence of different and complex dissipation mechanisms) still needs to be made available. The proposed work will focus on the formulation of path-following algorithms adapted to simulate RC structures.
ACCELERATING a DSN SWEEP KERNEL ALGORITHM FOR NEUTRONICS BY PORTING ON GPU.
In the framework of the Programmes Transversaux de Compétences (PTC or literally Cross-XXX Programme), the DES/ISAS/DM2S/SERMA/LLPR and the CEA-DIF are both working on the porting of deterministic neutron transport codes on GPU.
The DM2S within the Energies Direction (DES) is responsible for research and development activities on the numerical methods and codes for reactor physics, amongst which the APOLLO3® code. The neutronics laboratory of CEA-DIF is responsible for developing tools for deterministic methods in neutronics for the Simulation programme.
These two laboratories are actively preparing for the advent of new generation of supercomputers where GPU (Graphical Processing Units) will be predominant. Indeed, the underlying numerical problems to be solved along with the working methodology as well as the conclusions and experience which will be obtained from such studies may be rationalised between both laboratories. Thus, this work has given rise to this postdoctoral position which will be common to both teams. The postdoctoral researcher will be formally based at SERMA at CEA Saclay, with nevertheless regular meetings with the CEA-DIF scientists.
The postdoctoral research work is to study the acceleration of a toy model of a 3D discrete ordinates diamond-differencing sweep kernel (DSN) by porting the code on GPU. This work hinges on porting experiments which have previously been carried by both teams following two different approaches: a ‘’high-level’’ one based on the Kokkos framework for DES and a ‘’low-level’’ approach based on Cuda for CEA-DIF.
Multi-scale modelling of the structure and mobility of small defect clusters in metals
Recently, we have proposed a three dimensional periodic structure for self-interstitial clusters in body-centered-cubic metals, as opposed to the conventional two dimensional loop morphology [1]. The underlying crystal structure corresponds to the C15 Laves phase. Using Density Functional Theory and interatomic potential calculations, we have demonstrate that in a–iron these C15 aggregates are highly stable and immobile and that they exhibit large antiferromagnetic moments. They form directly in displacement cascades and they can grow by capturing self-interstitials. They thus constitute an important new element to account for when predicting the microstructural evolution of iron base materials under irradiation.
Despite their low concentration, these clusters are expected to play a crucial role in the behavior of iron and ferritic steels under irradiation and many questions remain to be elucidate: which clusters are the most stable in intermediate sizes, which are the reaction pathways which link the traditional clusters to new ones, how the new clusters interact with the dislocation loops, which are the effects of finite temperatures etc
Kinetic study of biocide effect in nanocellulose_based food film
This project will study the kinetic of biocide effect of a nanocellulose-based film food. The main aim is to graft Ag and/or ZnO NPs on and inside halloysite particles that have a characteristic shape of twisted sheets and therefore could acting as NPs tanks. The localization of NPs outside halloysite could induce a fast biocide effect with limited duration whereas the internal grafting could produce longer biocide effect. This project gathers all steps from the film food synthesis, its nanocharacterization to the evaluation of its toxicological effect on bacteria. The final goal is to find one or many halloysite functionalizations allowing to extend the biocide effect in film food and to transpose it to other types of materials.
xenon measurement by Cavity RingDown Spectroscopy to improve safety in the fast neutron reactors
Safety is a key point of the IVth generation nuclear reactors. Therefore new analytical methods are investigated for reliably detecting tracers of a nuclear reactor malfunction. This postdoctoral work aims at studying an innovative laser absorption method, Cavity RingDown Spectroscopy CDRS, to measure gaseous tracers indicating a reactor malfunction. This study is part of the research and development activity of the Physical Chemistry Department (DPC), which is partly involved in improving and developing tools and analytical methods. The optical system studies are a collaboration work with the "Laboratoire Interdisciplinaire de Physique" of the Grenoble University (France), which is a leader research laboratory in trace gas detection by laser absorption methods CRDS (Cavity RingDown Spectroscopy) and OF-CEAS (Optical Feedback Cavity Enhanced Absorption Spectroscopy).
A glow discharge was coupled to a Cavity RingDown measurement. After plasma conditions optimization, the optical set-up is able to measure below 1 part per billion Xe/Ar mixing ratios. The optical saturation of the xenon electronic transition should be considered to quantify each isotope. The optimized CRDS measurement will be characterized. The set-up could further measure krypton isotopes.
A. Pailloux & al., depot de brevet 11 62436 (2011)
P. Jacquet, A. Pailloux, submitted to J. Anal. Atom. Spectrom. (2013)
N. Sadeghi, J. Plasma Fusion Research 80 (9), pp 767-776 (2005)
Neutronic thermal-hydraulic coupling in heterogeneous Sodium Cooled Fast Reactor (SCFR)
Within the frame of ASTRID (Sodium cooled Fast Reactor) prototype development, update of calculation methodologies using new generation of codes benefiting from High Performance Computing (HPC) and advanced coupling capabilities is underway. These methods are expected to be integrated in ASTRID safety demonstration. In particular, development of coupled neutronics/thermal-hydraulics/fuel mechanics methodologies during accidental transients is underway.
Coupling Neutronics and thermal-hydraulics in double phase flow conditions (either sodium + vapor sodium or sodium + other gaz) can be used for:
• Loss of Flow transients (LOF, sodium + vapor sodium)
• Gas insertion transients.
This coupling is of special interest with cores strongly relying on axial leakage for safety consideration (like CFV cores [ICAPP11]).
The work proposed is to further develop the implementation of 3D coupling with state of the art CEA codes (APOLLO3, FLICA, CATHARE, TRIO etc.) to analyze the two type of transients stated above.