RSS export of vacancies - Seulement les offres à la une : No / Profil : Physique corpusculaire et cosmos, Physique théorique, Sciences pour l'ingénieur

SL-DES-24-0191 - Glass gaskets sealing characterization and modeling for High-temperature steam electrolysis technologies

Wed, 11 Oct 2023 02:15:12 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Carbon free hydrogen production is a key challenge for the energy mix of the future. One of the technologies identified is based on high-temperature steam electrolysis (HTE). The operating conditions of this process require the development of specific glass gaskets to seal the electrolysis cells. The technical issues with these gaskets are directly related to the loss of seal occurring because of interface adhesion problems or material cracking during HTE thermal cycling. The objective of this PhD work is to study the sealing performance of the glass gasket. Firstly, leakage tests will be carry out to discriminate the origin of seal loss according to the selected glasses. Then, mechanical characterization of the glass at high temperature will be performed in order to build the constitutive equation of the material. The overall PhD work will establish a link between the physico-chemical properties of glass and its mechanical and sealing properties. The results of the experimental tests and modeling will issue recommendations on the glass gasket to ensure the proper electrolyzer operation at industrial scale. The thesis is part of the development of HTE technologies in sight of an industrial-scale production. The project is based on a close collaboration between GENVIA (CIFRE thesis), CEA (ISEC) and the Institute of Physics of Rennes. Applicant must hold a master’s degree or an engineering degree in material sciences. The student will have to acquire extensive knowledge in mechanic, a first experiment in this field will be highly appreciated. Applicant is expected to show good synthesis and communication skills in order to collaborate with the various teams involved in the project. The expertise developed in glass mechanics and the experience acquired in the HTE field will be an asset for the future PhD. It is a great opportunity for the student to take advantage of his scientific knowledge to support the energy transition.

Glass gaskets sealing characterization and modeling for High-temperature steam electrolysis technologies

SL-DES-24-0186 - Predictive modeling of the alteration of nuclear waste containment glass.

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
In France, vitrified waste from nuclear fuel processing is to be disposed deep underground in clay geological strata. In this confined, low-porosity environment, the chemical interaction between the glass, the corrosion products of the metal containers and the site clay should control the weathering of the glass once the medium is again saturated with water. Predicting the long-term weathering of vitrified packages requires a thorough understanding of the many interrelated reaction mechanisms involved. In practice, these mechanisms are classified according to their importance on weathering kinetics, and then integrated within models adapted to the relevant time and space scales. This thesis focuses on the geochemical modeling of glass weathering, which is carried out using a reactive transport code (CHESS/HYTEC), a thermodynamic database and a kinetic law for glasses (GRAAL2 model, derived from the GRAAL model (Frugier et al. 2018)). This model takes into account the role of the composition of the glass weathering layer on its protective character, enabling GRAAL2 to simulate variations in weathering rate as a function of glass composition and environmental conditions.

Predictive modeling of the alteration of nuclear waste containment glass.

SL-DES-24-0078 - Study and implementation of photocatalysis in a Taylor-Couette reactor

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Heterogeneous photocatalytic reactions are considered as a promising path in mitigating ecological impacts. The efficiency and safe operation of these reactions are of crucial importance for large-scale applications. To exploit these reactions on a large scale, it is essential to study the factors that influence their effectiveness. These factors include the transmission of light in the system, the hydrodynamics of the reactor, the specific chemical reactions involved and, above all, the coupling of all these elements. In this PhD subject, the versatility of the Taylor-Couette flow will be exploited, which allows the flow to go from a plug flow to high turbulence in the same apparatus, while allowing high illumination thanks to a maximised surface/volume ratio, making it possible to study these different phenomena and their coupling. The study will rely on Monte Carlo and DNS (Direct Numerical Simulation) modeling to respectively describe the behavior of light and multiphase flow in the reactor. This will help identify and study influential parameters such as flow structure, spatial distribution of particles, photon transport, and photon-matter interactions within the reactor, not to mention the role of the gas phase. These models will be compared to experimental results obtained on a dedicated optical test rig and will contribute to a deeper understanding of the important processes at play in these photo(bio)reactors. The thesis is located in Marcoule CEA research center, near Avignon, in a multidisciplinary team with a strong focus on processes for green transition. The applicant we are looking for is an engineer and/or master 2 having a generalist profile and interested in playing an active role in this field. At the end of this Ph.D., the candidate will have a first experience in the present issues of low carbon energies in circular economy. Such a type of versatile profile will undoubtedly be an asset for a future career in academia as well as in industry.

Study and implementation of photocatalysis in a Taylor-Couette reactor

SL-DRT-24-0106 - Artful guidance of test generation tools

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Fuzzing is an automatic test generation technique. It consists in repeatedly executing a program with automatically generated inputs, in order to trigger crashes, symptoms of underlying bugs in the code, which can then be fixed. A major challenge in this area is moving from indiscriminate exploration of how programs work to artful guidance towards the discovery of important bugs. Taking advantage of the expertise of our team and our previous work, the objective of the thesis is to propose, implement and evaluate means to meet this challenge, taking advantage of finer-grained guidance mechanisms.

Artful guidance of test generation tools

SL-DES-24-0064 - Contribution of Artificial Intelligence in Establishing Three-Dimensional Contamination Mapping within C

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Understanding the radiological inventory of a nuclear installation is paramount to ensure the control of safety and criticality risks throughout the facility's lifespan, as well as to manage the radiological impact on both human health and the environment. Managing the radiological condition of the processes and equipment within an installation enables the definition of safe intervention scenarios to optimize maintenance operations or decontamination/dismantling activities in hostile environments and enhance waste management. During the dismantling of a nuclear facility, decontamination operations are necessary to reclassify areas from nuclear waste zones to conventional waste zones. This step necessitates the prior creation of an accurate map of artificial radioactivity within the concrete civil engineering structures. To address the limitations of existing methodologies and in accordance with the directives of the Nuclear Safety Authority (ASN), the proposed doctoral research aims to develop an innovative and efficient non-destructive radiological characterization methodology using machine learning algorithms (artificial intelligence) for automated analysis of in-situ gamma spectrometry measurements with a highly resolved Germanium detector. The ultimate goal is to establish real-time three-dimensional maps of contaminant distribution within contaminated civil engineering structures of nuclear facilities. The characterization methodology developed as a result of this project holds significant potential for industrial applications, particularly in the field of nuclear facility decontamination and dismantling. The doctoral candidate will work within a team with extensive experience in the development and in situ implementation of non-destructive radiological characterization techniques (alpha and gamma imaging techniques, alpha, beta, and gamma spectrometry techniques). The candidate will have the opportunity to evaluate the proposed solutions on some of the world's largest dismantling sites. The desired profile is a candidate with an engineering school or Master's degree (M2) background and strong knowledge in nuclear instrumentation and measurement, particularly in the physical phenomena related to the interactions of ionizing radiation with matter. Proficiency in statistical data processing methods and machine learning (computer programming in Python) is also highly valued.

Contribution of Artificial Intelligence in Establishing Three-Dimensional Contamination Mapping within Civil Engineering Structures of Nuclear Facilities using Gamma Spectrometry Measurements

SL-DES-24-0086 - Automatic reverse-engineering of BIM models using Machine Learning

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Today, BIM (Building Information Modelling) has become a standard for information management in factories, buildings and industrial facilities. The BIM approach is particularly well-suited to complex industrial environments, and nuclear facilities in particular, as it proves to be a relevant tool throughout the facility's lifecycle, from design to construction, operation and decommissioning, by offering shared, smart and structured modelling. This approach is centered on a 3D model, generally produced from a point cloud obtained by lasergrammetry. In most cases, panoramic photos can be acquired at the same time. From this point cloud, a 3D model is generally rebuilt to represent the equipment present as set of single solid objects. This 3D model reconstruction stage is often long and tedious, and is currently carried out manually by a CAD designer. This thesis proposes to develop an automatic method for reconstructing BIM models from point clouds using machine learning and image analysis, exploiting both the point cloud and available panoramic photos. The environments of nuclear facilities are composed of very specific steel or alloy processes, and mainly include piping equipment. By combining machine learning and computer vision, using both clustering and classification methods on the one hand, and shape and image recognition on the other, the work consists in directly identifying in the point cloud objects belonging to business object families such as pipes, elbows, valves, supports, fittings, tanks, etc., as well as some of their metadata: the material they are made of, their geometric properties (diameter, thickness, length), their volume and mass.

Automatic reverse-engineering of BIM models using Machine Learning

SL-DES-24-0091 - Development of methodologies for testing electronic systems in irradiating environments

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Decontamination and dismantling (D&D) worksites, and more generally nuclear facilities, involve the use of electronic equipment (sensors, mobile vectors, robots, remotely operated arms, etc.) in harsh environments. Radiation is one of the main factors affecting the reliability of electronic components and systems. In this context, the evaluation of electronic components and systems makes it possible to identify which technologies are most tolerant to irradiating environments, and also to determine which sub-functions are the most sensitive. To address this challenge, it is necessary to develop electronic qualification methodologies for the nuclear field, based on experience from the space field but taking into account certain specific features: the environment can be much more extreme, the use of commercial components is widespread, and a system-level approach must be considered (as it is not possible to develop everything from the component upwards). System-level testing and the use of COTS components in irradiating environments are emerging issues of interest to many stakeholders. The thesis work will therefore begin with the study of specifically developed systems. We will then have a complete understanding of the system and, above all, of the elementary components that make it up. We'll be able to characterize each elementary component and the complete system under a single beam. The degradation synergy between the system and the elementary component will be studied to evaluate degradation rules, before moving on to the implementation of methodologies that can then be evaluated on commercial 'black box' systems. The aim is to verify that the conclusions reached in the first stage are still valid, and to determine the observables needed to identify a failure. Innovative AI-based data analysis methods can also be implemented, depending on the type and quantity of data collected. Given the expected numbers of systems to be tested, it is also essential to complement this work with a rationalization of irradiation resources. To this end, tests will be carried out, notably on the filtering of X-ray photons in the photoelectric range to keep only the Compton range and thus have an equivalence to Cobalt60. Finally, a methodology will have to be implemented. This methodology will have to take into account system procurement, definition of observables, definition of irradiation and characterization conditions, as well as analysis of the elementary and functional failures observed. Part of the thesis work will also involve defining the structure of a 'radiation' database for listing radiation tests carried out on electronic components and systems.

Development of methodologies for testing electronic systems in irradiating environments

SL-DAM-24-0028 - Analysis of the dynamic response of Molybdenum to a laser shock

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Since recently, Molybdenum has been considered as a material of interest in many dynamic configurations, especially in Defense applications such as for shaped charge liners, where extreme dynamic loadings (high strain rates, large strains, high pressures …) are encountered. Nonetheless, this material has been essentially characterized through quasi-static experiments or under extreme pressures related to planetology issues for instance. At the meantime, laser shock experiments have gained in importance. Indeed, compared to other dynamic loading techniques (impacts, explosives …), laser-driven shocks offer a large loading range capability (by varying intensity, size and duration of the laser pulse), some insight into the plastic behavior of the materials at extremely high strain rates, and easy sample recovery for a variety of post-mortem analyses. The main objective of this PhD, co-supervised by Institut Pprime (CNRS, ISAE-ENSMA) in Poitiers (France), is to characterize the behavior of laser shock-loaded Molybdenum over a range of loads representative of shaped charges, to test and to improve whenever possible the predictive capabilities of existing models. Innovative configurations will be studied. For that purpose, the student will have to design, to carry out and post-process various laser shock experiments so as to : - Characterize the elasto-plastic behavior of Molybdenum through time-resolved velocity measurements and possibly temperature measurements ; - Realize post-mortem analyses on Molybdenum specimens ; - Analyze the implosion phase representative of what generates shaped charges jets on notched specimens ; - Analyze the effects of inclined shocks on Molybdenum.

Analysis of the dynamic response of Molybdenum to a laser shock

SL-DAM-24-0024 - Stability of ablation flows in inertial confinement fusion: transient growth

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Inertial confinement fusion (ICF) aims at producing energy from thermonuclear fusion reactions between low atomic-number elements. A possible approach for reaching the high densities and temperatures needed for triggering these reactions, consists in imploding a spherical capsule, filled with a mixture of fusible elements, by means of a high energy density irradiation. This irradiation induces a violent vaporization – ablation – of the capsule outer shell that drives the implosion. The finite duration of these implosions emphasize the need for investigating possible perturbation transient growth that may dominate the flow over short-time horizons. For this project, we wish to investigate such transient growth in strongly accelerated self-similar ablation flows, with planar of spherical symmetry, which are relevant to the main stage of an implosion. This work will be carried out using a direct-adjoint method of non-modal stability theory, previously devised for weakly accelerated self-similar ablation flows in planar symmetry, that will have to be adapted to handle strongly accelerated configurations. Results could be used to setup, in a more realistic setting, `multi-physics' simulations of capsule implosions.

Stability of ablation flows in inertial confinement fusion: transient growth

SL-DAM-24-0012 - Relativistic laboratory astrophysics

Wed, 11 Oct 2023 02:15:11 Z

Category : Corpuscular physics and outer space
Contract : Thèse
Thesis topic details :
This PhD project is concerned with the numerical and theoretical modeling of the ultra-relativistic plasmas encountered in a variety of astrophysical environments such as gamma-ray bursts or pulsar wind nebulae, as well as in future laboratory experiments on extreme laser-plasma, beam-plasma or gamma-plasma interactions. The latter experiments are envisioned at the multi-petawatt laser facilities currently under development worldwide (e.g. the European ELI project), or at next-generation high-energy particle accelerators (e.g. the SLAC/FACET-II facility). The plasma systems under scrutiny have in common a strong coupling between energetic particles, photons and quantum electrodynamic effects. They will be simulated numerically using a particle-in-cell (PIC) code developed at CEA/DAM over the past years. Besides the collective effects characteristic of plasmas, this code describes a number of gamma-ray photon emission and electron-positron pair creation processes. The purpose of this PhD project is to treat additional photon-particle and photon-photon interaction processes, and then to examine thoroughly their impact and interplay in various experimental and astrophysical configurations.

Relativistic laboratory astrophysics

SL-DES-24-0009 - Using Bayesian methods to locate nuclear material in heterogeneous media by active photon interrogation

Wed, 11 Oct 2023 02:15:11 Z

Category : Corpuscular physics and outer space
Contract : Thèse
Thesis topic details :
The characterization of radioactive waste from the nuclear industry is essential to ensure their sustainable management, in compliance with French regulations. CEA is developing methods using ionizing radiation to verify the contents of waste packages. Active photon interrogation (API) is a non-destructive technique well suited to large-volume compacted waste, where other techniques fail. It uses an interrogator beam of high-energy photons, capable of inducing fission in nuclear material, in order to estimate its quantity. The current challenge is to rapidly localize nuclear materials within the package, so that focused spectrometry techniques can then be applied to identify fission products. This is an inverse problem, involving the determination of a radiation source (induced by photofission) from a limited set of measurements. The aim is to develop a Bayesian formalism for dealing with this problem in realistic cases, taking into account the uncertainties related to nuclear data, to the interrogating beam flux, to measurements statistics and to the waste package characteristics (density, composition). Cases of increasing complexity will be studied: homogeneous medium, then heterogeneity, introduction of the 3D density map of the medium obtained by X-ray tomography and the presence of several sources. Experimental validation will be based on the experimental resources of the Laboratoire de Mesures Nucléaires (LMN) at CEA Cadarache, where the thesis will be carried out, including the CINPHONIE irradiation cell where a 15 MeV electron LINAC is installed, nuclear material samples and mock-up waste packages.

Using Bayesian methods to locate nuclear material in heterogeneous media by active photon interrogation

SL-DRF-24-0102 - Imaging with Micromegas detectors with Optical readout

Wed, 11 Oct 2023 02:15:11 Z

Category : Corpuscular physics and outer space
Contract : Thèse
Thesis topic details :
Recent developments have shown that coupling a Micromegas gaseous detector on a glass substrate with a transparent anode and a CCD camera enable the optical readout of Micromegas detectors with an impressive spatial resolution showing that the glass Micromegas detector is well-suited for imaging. This feasibility test has been effectuated with low-X-ray photons permitting energy resolved imaging. This test opens the way to different applications. Here we will focus, on one hand, on neutron imaging for non-destructive examination of highly gamma-ray emitting objects, such as fresh irradiated nuclear fuel or radioactive waste and on the other hand, we would like to develop a beta imager at the cell level in the field of anticancerous drug studies. Both applications require gas simulations to optimize light yields, optimization of the camera operation mode and design of the detectors in view of the specific constraints of reactor dismantling and medical applications: spatial resolution and strong gamma suppression for neutron imaging and precise rate and energy spectrum measurements for the beta. The image acquisition will be optimized for each case and dedicated processing algorithms will be developed.

Imaging with Micromegas detectors with Optical readout

SL-DRF-24-0046 - Alignment of the muon spectrometer and measurement of the electroweak mixing angle at the TeV scale

Wed, 11 Oct 2023 02:15:11 Z

Category : Corpuscular physics and outer space
Contract : Thèse
Thesis topic details :
This thesis project concerns the precise measurement of the electroweak mixing angle with the ATLAS experiment, at the LHC. The evolution with energy of this fundamental parameter will also be tested. The measurement will be based on the di-muon data set from runs 2 and 3 of the LHC, and will use the muon spectrometer as the main instrument. The determination of the mixing angle is based on the measurement of the forward-backward asymmetry of the Z boson decay muons. For precise control of systematic uncertainties, the internal alignment of the spectrometer must be optimized. This alignment constitutes an important part of the project. The performance of the New Small Wheel, the new muon detector installed for run 3, will also need to be understood in detail. The actual measurement will be carried out at the end of these preliminary studies, and an interpretation of the result will complete the thesis.

Alignment of the muon spectrometer and measurement of the electroweak mixing angle at the TeV scale

SL-DES-24-0196 - Modelisation of a liquid fed cold crucible inductive melter during HLLW vitrification

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
The vitrification of high level liquid waste (HLLW) resulting from the reprocessing of spent fuel is carried out, in part, in a furnace known as an inductive cold crucible melter at 1200 ° C. The waste initially in liquid form is introduced into the oven after a drying and calcination step. The work of this thesis is part of studies aiming to feed the waste in the furnace directly in liquid form. The first objective is to be able to simulate the mixture between molten glass and liquid waste at the surface from the point of view of fluid mechanics, thermal and chemical engineering. The second objectives is to simulate thixotropic behavior of the glass. Experimental data are already available, the law of viscosity of the glass will be a function of time and local shear rate. This modeling will be integrated into the magneto-thermo-hydraulic simulations of the processes already developed in the laboratory [1-3]. Comparisons between simulations and prototype experiments at a 1: 1 scale inactive, as well as discussions with American and Czech research teams are planned. [1] Barba Rossa, Thèse de doctorat, Modélisation multiphysique de l’élaboration de verre en creuset froid, 2018, https://www.theses.fr/2017GREAI050 [2] Paraiso K, Sauvage E, Schuller S, Hocine S, Lemaitre V, Burov E. Characterization and modeling of chemical reactions taking place during the vitrification of high level nuclear waste. Journal of Nuclear Materials. 2022, 569, 153878 [3] Pereira Machado, N.M., Neyret, M., Lemaître, C. et al. Thixotropic behavior of a glass melt of nuclear interest containing platinum group metal particles. Rheol Acta (2022). https://doi.org/10.1007/s00397-022-01372-x [4] Chun, J.; Pierce, D. A.; Pokorny, R. & Hrma, P.; Cold-cap reactions in vitrification of nuclear waste glass Experiments and modeling; Thermochimica Acta , 2013, 559, 32 – 39

Modelisation of a liquid fed cold crucible inductive melter during HLLW vitrification

SL-DES-24-0155 - Ab-initio nuclear cross section modeling combining R-matrix theory and self-consistent Green functions

Wed, 11 Oct 2023 02:15:11 Z

Category : Theoretical physics
Contract : Thèse
Thesis topic details :
Microscopic nuclear physics aims at describing structure and reaction properties of atomic nuclei starting from nucleonic scales and using the elementary interaction between nucleons as the basic input. Ab-initio methods use systematic interactions derived via effective theories of underlying Quantum Chromo-Dynamics and adjusted on properties of light systems. Most methods describing N interacting quantum bodies rely on the estimation of a wave function that is the solution of an N-body Schrödinger-type equation. Self-consistent Green’s function theory works differently, as it recasts the N-body problem by substituting suitably chosen Green’s functions for the wave function. An interesting aspect of Green’s function theory is that it involves a systematically improvable field – the self-energy – describing the interaction “felt” by the nucleon. This field, used in structure calculations, can thus also be used for describing nuclear reactions. The PhD student will first study the formalism and learn how to use related tools, namely the spherical HFB code sPAN, which provides first-order contributions to the Green’s functions. The student will then implement second-order descriptions. Finally, the obtained self-energy will be used for nuclear reaction calculations, namely in the context of R-matrix theory. The latter is a convenient tool to describe (unbound) nucleons in the continuum, treating both the direct and exchange parts of the nucleon-nuclei interaction.

Ab-initio nuclear cross section modeling combining R-matrix theory and self-consistent Green functions

SL-DES-24-0127 - Impact of ultrasound on the flow properties of complex suspensions

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Nuclear industry generates radioactive wastes of various nature such as solids, liquids but also sludges coming from effluent treatment facilities or historical residues stored in pool or tanks. The physico-chemical nature of those sludges leads to a complex flow behaviour making it difficult to handle and convey prior their immobilization in a conditioning matrix. In order to fluidize these suspensions of varying compositions, the mechanical action of power ultrasound is envisaged. It has recently been shown, thanks to a set-up coupling power ultrasound and rheology, that it is possible to significantly reduce the yield stress and viscosity of the slurry by applying ultrasound. The aim of this thesis is to pursue the studies already undertaken (physical chemistry, microstructure, ultrasound and rheology) on reconstituted sludge or simplified model suspensions, focusing more specifically on two aspects. The first, more fundamental, will aim to gain a better understanding of the interaction between power ultrasound and matter, with a particular focus on the origin of the effects observed (interfaces vs. volume). The second aspect will be more applied, with the development of original larger-scale experimental devices capable of generating flows closer to industrial situations.

Impact of ultrasound on the flow properties of complex suspensions

SL-DES-24-0216 - Modélisation simplifiée de la calcination en tube tournant

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
Dans le cadre du retraitement des combustibles usés de type uranium oxyde, les déchets liquides ultimes de haute activité sont conditionnées dans des verres par un procédé en deux étapes, calcination puis vitrification. La calcination transforme progressivement le déchet liquide en un résidu sec, qui est mélangé à un verre préformé dans un four de fusion. Le calcinateur est constitué d’un tube tournant chauffé par un four à résistances. Les solutions calcinées sont constituées d’acide nitrique et de composés sous leur forme nitrate ou d’insolubles sous forme d’alliages métalliques. Dans l’objectif d’améliorer la maîtrise du pilotage du calcinateur, il est proposé de le modéliser. La modélisation va consister à créer puis coupler trois modèles : • Un modèle thermodynamique permettant de représenter les transformations subies par la matière. Cette partie fera très certainement appel à des mesures ATD et ATG, couplées très certainement à une démarche de type plan d’expériences (1ère année). • Un modèle d’écoulement de la matière. Il existe déjà dans la littérature des principes de représentation très simplifié d’écoulement dans un calcinateur en tube tournant, mais il faudra faire preuve d’innovation notamment en définissant des tests pour caractériser l’écoulement de la matière au cours du processus de calcination (2ème année). • Un modèle thermique qui prendra en compte les échanges entre le four et le tube du calcinateur mais également les échanges entre la matière et le tube. Des caractérisations de coefficients d’échanges devront être réalisées(1ère année). Le couplage de ces trois modèles (3ème année) donnera naissance à une première modélisation simplifiée de la calcination. Ce modèle sera utilisé pour aider au pilotage de l’étape de calcination mais également pour former les opérateurs au pilotage de cet appareil. Vous évoluerez au sein du LDPV, une équipe pluridisciplinaire (procédé, chimie, mécanique des fluides, modélisation, mécanique, induction) composée de 16 ingénieurs et techniciens. Equipe de 30 ans d’expérience en procédé de vitrification reconnue au niveau national et international

Modélisation simplifiée de la calcination en tube tournant

SL-DES-24-0202 - Study of the prototypical corium solid state containing fission products crystallographic and microstruc

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
In a moderated and/or water-cooled nuclear reactor, a loss of cooling systems may result in partial or total melting of the core, which may then interact with any water present in the vessel or outside the vessel, as it happened during the Fukushima-Daiichi nuclear accident in 2011. The study of the interactions between corium and water is now a prerequisite for defining the source terms for radionuclides in the course of serious accidents that may escape from the containment by alteration and leaching, whether with residual water from the reactor or by a later voluntary injection of water or with environmental water. This requires a better knowledge of the crystallographic structures of coriums concretes incorporating fission products and their mechanism of interaction and release during contact with water. In order to provide answers, this thesis project is part of an original experimental approach by combining structural and microstructural studies on prototypical coriums concrete in which stable isotopes simulating fission products present in corium have been introduced, to leaching tests. The materials based on siliceous and silico limestone concrete developed on the PLINIUS Platform of the CEA Cadarache, will be characterized at the LMAT laboratory of the CEA of Marcoule by the use of different techniques in surface analysis (MEB, EDS, WDS Castaing microprobe for elementary measurement of contents less than 1% mass). The study of phase formation in coriums concretes (segregation, crystalline and amorphous forms) can be conducted by crystallographic analysis performed by diffraction techniques at the SOLEIL synchrotron and by neutron diffraction at the ILL. Fine crystallographic analysis will implement the Rietveld method. The properties of the micro texture can be qualified on solid material and thin film by EBSD, TKD, DRX, and by Laue micro diffraction in the ESRF synchrotron. First leaching tests under oxidative conditions will be carried out with the LEMC laboratory of the CEA of Marcoule in parallel to the characterization campaigns in order to identify the main mechanisms of weathering. This knowledge will feed into a database of 'serious accident materials' useful for the management of coriums during the accident and beyond. The skills acquired by the doctoral student around the characterization of materials may be valuable for the doctoral student in many fields in materials science. The profile of the student will require knowledge of materials and instrumentation. The theme «serious accident» and interaction with water will also be of interest to the doctoral student in the field of environment and more particularly discharges.

Study of the prototypical corium solid state containing fission products crystallographic and microstructural analysis impact on weathering and leaching mechanisms

SL-DES-24-0007 - Study of plastic scintillators for passive and active neutron measurements

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :
The proposed doctoral work is dedicated to optimizing non-destructive characterization methods for the quantity of plutonium in radioactive waste packages. One of the primary nuclear measurement methods to achieve this goal is based on the passive counting of coincidences between spontaneously fissioned neutrons. Most neutron measurement stations are equipped with 3He counters, which have the advantage of good detection efficiency while being less influenced by gamma radiation. However, the price of these detectors has significantly increased in recent years, and they are relatively slow as they require prior thermalization of the neutrons to be detected. Plastic scintillators offer a 5 to 10 times less expensive alternative with equivalent detection efficiency, making them attractive for implementation in industrial stations. In exchange, they are highly sensitive to gamma radiation and the phenomenon of crosstalk (parasitic coincidences due to interactions between neighboring detectors). An innovative method for discriminating between useful and parasitic coincidences by differentiating the time of flight between neutrons and gamma radiation has been developed and validated in previous work. There are still significant practical challenges addressed by this thesis in order to move towards an industrial neutron measurement station equipped with these scintillators, particularly for technological waste (ORANO La Hague, MELOX Cadarache). The primary objective in passive neutron measurement will be to advance in detection efficiency, data processing, and reducing uncertainties related to matrix effects and nuclear material localization, closely integrating experiments and modeling. A secondary objective of the thesis will be to demonstrate the feasibility of active neutron measurement in terms of data processing and resilience to high counting rates for quantifying the mass of nuclear material (detection of neutrons induced by a neutron generator).

Study of plastic scintillators for passive and active neutron measurements

SL-DAM-24-0041 - Modeling of electronic components and functions in a radiative environment

Wed, 11 Oct 2023 02:15:11 Z

Category : Engineering science
Contract : Thèse
Thesis topic details :

Modeling of electronic components and functions in a radiative environment