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.
New Sustainable Carbon Catalysts for PEMFC
The aim of the project is to develop and test for ORR, a mesoporous and graphitised graphene aerogel based material, presenting a hierarchical structuring allowing a better material transfer and graphitic domains increasing the durability and conductivity of the final material, and functionalised by Pt-NPs.
These graphene-based structures developed at IRIG/SyMMES possess surface chemistries and micro/meso/macro porosities that depend on the synthesis, functionalisation and drying methods used. The aim will be to increase their degree of graphitisation, and then to deposit Pt-NPs by chemical means. The electrocatalytic properties of these materials will then be tested.
Advanced meso-structural characterisation of these materials by scattering (X-ray or neutrons) methods will enable to investigate the structural properties of these new electro-catalysts. These properties will thenbe correlated to their electrocatalytic properties, and performances in fuel cell systems. This knowledge will be gained through ex-situ and operando analyses.
Development of Monte-Carlo methods for the simulation of radiative transfer: application to severe accidents
This post-doctoral subject concerns the development of Monte-Carlo ray-tracing methods for modeling radiation heat transfer in the context of severe accidents. Starting from a well-developed software framework for Monte Carlo simulation of particle transport in the context of reactor physics and radiation protection, we will seek to adapt existing methods to the problem of radiative heat transfer, in a high-performance computing framework. To do this, we will develop a hierarchy of approximations associated with radiative heat transfer that are intended to allow the validation of simplified models implemented in the context of the numerical simulation of severe accidents in nuclear reactors. Focusing on algorithm and simulation performance, this work is intended to be a "proof of principle" of the possible software mutualization around the Monte-Carlo method for particle transport on the one hand and radiative heat transfer on the other hand.
CIGS solar cells optimized for energy harvesting applications in indoor environments
The goal of this post-doctoral fellowship is to develop solar cells based on CIGS thin films, for energy harvesting applications (powering of small electronic autonomous devices). This research project will aim at optimizing the solar cell performances in indoor environments, i.e., under low light intensity. The post-doctoral fellow will be involved in CIGS thin film elaboration by physical vapour deposition, film characterization, solar cell realization and test.
Characterisation of vanadium alloys
Vanadium alloys, investigated in the scope of application in fusion reactors, are potential candidates for fuel cladding of future sodium cooled or gas cooled fasts reactors. Then, in 2009, CEA launched a program aiming to assess this solution according to future reactor requirements.
Preliminary investigation of V-4Cr-4Ti plates was done at DMN/SRMA/LA2M (i) on a reference Japanese grade and (ii) on a specific grade fabricated for CEA study. Works haw focuses on recrystallisation structure after cold working (grain size and morphology, effect of annealing temperature), and on fine microstructure (occurrence of Ti(O,C,N) precipitation). In 2011, fabrication of vanadium tube by hot extrusion is planned to be relevant of the final cladding geometry. The proposed post-doc investigation aims to monitor the fabrication and to specify the impact of fabrication process on microstructure, recrystallisation dynamic and mechanical properties.