Development of a digital twin of industrial equipment: coupling chemistry / thermo-hydraulics / corrosion
This PhD subject is part of CEA R&D aimed at developing and improving decarbonized technologies for energy production, in response to climate issues. More specifically, it is part of the spent fuel reprocessing stage used in current nuclear reactors. The simulation of the operation and aging of this equipment is a major challenge for the sustainability of the activities of fuel reprocessing plants.
The objective of the thesis is to respond to these challenges, by developing a modeling of the corrosion of one or more equipments in the plants based on their operation. This will require coupling chemical reaction models (in solution and corrosion) with thermo-hydraulic models. These developments will be carried out using modeling tools developed by the CEA.
By making it possible to simulate the corrosion of equipment, the development of such a model will make it possible to optimize its lifespan (by seeking to optimize its operation, for example) or to accurately estimate (and therefore anticipate) the time needed for its replacement.
Development of an automated and miniaturised system for the isotopic analysis of nuclear samples
Miniaturisation, which is the process of reducing an object’s, a method’s or a function’s dimensions while preserving or even upgrading its performances as compared to the classical scale, has a particular interest in the field of analytical chemistry for nuclear applications. Indeed, most of the analyses are performed in gloveboxes where miniaturisation and automation are a direct solution to the need for reduced doses and waste volumes. This PhD aims at developing a miniaturised and automated system, in a glove box, for performing high-precision isotopic measurements. This system will use capillary electrophoresis (CE) hyphenated with a nuclearised multicollector ICP-MS (MC-ICP-MS). During this PhD, the student will make use of micro-machining machines and 3D printers to develop an ergonomic system which will then be coupled to last generation MC-ICP-MS instruments available in our laboratory. The project will be focused on the conception of the automated system and its integration in the glove box, and on the further development of the existing CE method in order to perform isotopic and elemental analyses with nuclear samples. This PhD is hosted in a laboratory internationally recognized for its ability to carry out high precision isotopic measurements. An analytical chemistry curriculum is expected and a Master 2 internship is available before this PhD.
Redox behavior of technetium in the innovative PUMAS process: kinetic and speciation study
Technetium (Tc), an artificial radioactive element, makes up about 6% of the fission products in spent nuclear fuel. The PUREX process is used to separate uranium and plutonium from other fission products. However, Tc is co-extracted with these actinides, requiring an additional stripping step. In this stage, a stabilizing agent, hydrazinium nitrate (NH), is used, but due to its toxicity and CMR classification (Carcinogenic, Mutagenic, Reprotoxic), it is being replaced by less toxic alternatives such as oximes. Although promising, oximes exhibit slower stripping kinetics compared to NH. In the context of the PUMAS process, this thesis aims to understand the complex redox mechanisms of Tc and the kinetic differences between oximes and NH. The PhD student will study the reduced forms of Tc and analyze the reduction kinetics in the presence of U(IV) and anti-nitrous agents. A methodology will be developed to characterize the oxidation states of Tc, and reaction rate constants will be determined as a function of temperature and reactant concentrations.
The candidate will work closely with the supervising team to develop autonomy, adaptability, and the ability to propose innovative ideas. By the end of this journey, the candidate will have gained not only advanced technical skills but also abilities in project management, collaborative work, and scientific writing and communication. These competencies will provide strong prospects for a career in academic research or industry.
Molecular Dynamics Simulation of Plutonium(IV) in Solution
With the revival of nuclear power in France, the CEA is playing a key role in the nuclear industry of the future. In this context, engineers and researchers are mobilised to meet the growing needs of this industry. Plutonium is a key element in the nuclear fuel cycle. Acquiring molecular data is crucial to optimising and rationalising the mechanisms involved in separating this element.
Plutonium(IV) is one of the most common cationic forms in the nuclear fuel cycle. Its study by theoretical chemistry presents difficulties both in ab initio modelling (occupied f-block orbitals) and in classical atomistic simulations. In classical molecular dynamics simulation, the models necessarily require the addition of the polarisation effect, and sometimes even the addition of charge transfer, in order to reproduce the system's behaviour correctly. As a result, classical simulations containing plutonium (IV) are almost completely absent from the scientific literature. In addition, the speciation of this cation is sensitive to the acidity of the medium, which has to be taken into account in the simulations, adding a further difficulty.
The aim of this thesis is to use molecular dynamics (classical and ab initio) to simulate solutions containing plutonium, taking into account the effect of acidity. The PhD student will be faced with two main issues: the choice or development of a force field for the Pu4+ cation, and the design of a method for including acidity in the solutions. A crucial step in the process will be to compare the results with the available experimental data in order to conclude on the ability of the models to reproduce the experimental data. This thesis will be carried out in a multidisciplinary laboratory, combining experimental chemistry and theoretical modelling, while conducting both applied and fundamental research.
Brittle fracture of low alloy steels: sensitivity of mesosegregation regions to quenching and tempering conditions
The pressure vessels of the primary circuit of French nuclear power plants are made by assembling low-alloy steel components, forged from high-tonnage ingots (> 100t) that solidify in a non-uniform manner. The high thickness of the component also implies that the evolution of temperature during post-forging heat treatments vary significantly depending on the position in the thickness of the component. These two effects contribute to producing heterogeneous microstructures that can significantly weaken the material.
The scientific objective of this thesis is to evaluate which elements within the microstructure are responsible, and in what proportion, for increased embrittlement of the material for certain unfavorable heat treatment conditions. Conversely, better identifying the range of heat treatment conditions for which this embrittlement of the material remains contained, for a given initial microstructure, is an objective with high industrial stakes. Several heat treatments have already been applied to coupons from a rejected industrial component before subjecting them to Charpy impact toughness tests, in the field of the brittle to ductile transition of the material. Instrumented mechanical tests will be conducted as well as advanced fractographic and microstructural analyses in order to identify the evolution of the nature of the initiation sites according to the heat treatment conditions. These elements will then be integrated into a local approach to fracture model developed specifically to account for the effects of microstructural variations on the resistance to brittle fracture of low-alloy steels.
Flotation for Li-ion active materials recycling : limitations and influence of hydrodynamics and interfacial physico-chemistry on their selective separation
Battery recycling is now a major geopolitical, economic and environmental issue for the EU. Graphite, which makes up the anode of Li-ion batteries, is very rarely recycled. It is concentrated in a fraction called blackmass, where it is mixed with metal oxides of high commercial value. This graphite is then considered as an impurity and causes oversizing of hydrometallurgical operations. Since natural graphite is considered critical by EU and in order to reduce the operating and investment costs of hydrometallurgical processes, it is proposed to carry out a pre-treatment step on the blackmass in order to valorize the graphite directly. This stage is carried out by flotation. This process for separating solids suspended in water uses gas in the form of air bubbles to separate the particles according to their difference in wettability and therefore their attachment to the air bubbles. The complexity of the flotation process, linked to the dependence on both the nature of the interfaces and the hydrodynamic conditions, requires in-depth understanding of the mechanisms involved.
The aim of the proposed project, which follows on from two internal projects, is to identify the mechanisms at work during flotation, using methods of interfaces characterization, stability and rheology of foam fraction, imaging, etc., with a view to improving the performance of the flotation stage and extending it to other recycling challenges.
The PhD thesis work will be carried out at the Laboratoire des technologies de Valorisation des procédés et des Matériaux pour les ENR (LVME) at CEA Grenoble and in close collaboration with the Laboratoire de Caractérisations Avancées pour l'Energie (LCAE) at CEA Grenoble, the Laboratoire des Procédés Supercritiques et décontamination (LPSD) and the Laboratoire de développement des procédés de recyclage et valorisation pour les systèmes énergétiques décarbonnés (LRVE) at CEA Marcoule (30). In parallel with the experimental work, the models and mechanisms involved and the associated technical solutions will have to be proposed.
The scientific and industrial interest of the subject guarantees that the work will be promoted through international communications. After the PhD, you can join one of the best academic or applied research teams, or pursue an R&D career directly in industry.
Numerical simulation of the impact between immersed structures in a compressible liquid using immersed boundary type approaches.
Many industrial systems involve structures immersed in dense fluids. Examples include the submarine industry, or, more specifically, certain 4th generation nuclear reactors using coolant fluids such as sodium or salt mixtures. The effect of the interaction of the surrounding fluid on the contact forces between structures is a phenomenon of primary importance, particularly during accidental transient scenarios that can generate large displacements of structures whose residual integrity must be demonstrated for safety purposes.
In the context of this thesis, we are particularly interested in modeling the rapid impact of a structural fragment immersed in a fluid against a wall, resulting, for example, from an explosive phenomenon in a nuclear reactor vessel cooled by sodium. In this context, the sodium, modeled as a compressible fluid, is treated numerically using a volume-finite approach. The reactor's internal structures are treated using a finite-element approach. In order to deal with large structural displacements and possible fracturing, “immersed boundary” techniques are used for fluid-structure interaction.
The aim of this thesis is to define an innovative numerical method to better simulate the fluid film between two structures that come into contact in this context. Initially, we will focus on identifying the physical characteristics of the flow at the level of the fluid film (compressibility, viscosity, etc.) that have the greatest influence on the kinematics of the structures. Secondly, the main challenge of this thesis will be to improve current numerical methods in order to represent the flow characteristics of the fluid film as accurately as possible.
The proposed thesis will be carried out at CEA Saclay, in close collaboration with the EM2C laboratory at CentraleSupélec, within the environment of the Université Paris-Saclay. The PhD student will be immersed in a team with recognized expertise in transient simulations of fluid-structure interaction.
Impact of solvent nanostructure on uranium precipitation: a physicochemical approach for nuclear recycling
Recycling nuclear fuel is a major challenge to ensure a sustainable energy future. The CEA, in partnership with Orano and EDF, has been developing a new process for separating plutonium-rich fuels for several years. The goal is to replace the current TBP/TPH system with a redox-free process, better suited for the reprocessing of MOX or fast neutron reactors (FNR).
In this context, this thesis proposes to study the behavior of organic solvents loaded with uranium to understand and prevent the formation of precipitates, a phenomenon that could impact the performance of industrial processes. The scientific approach will focus on the supramolecular scale and compare different monoamides to evaluate the effect of alkyl chains on the physicochemical properties and nanostructure of the solutions.
The candidate should hold a Master's degree (Master 2) in chemistry, physical chemistry, or materials science. Skills in analytical chemistry, spectroscopy (NMR, FTIR), and scattering techniques (SANS, SAXS) will be highly valued. By joining this project, you will become part of the CEA's cutting-edge laboratories (ICSM/LTSM and DMRC/SPTC/LILA), equipped with world-class facilities for studying radioactive samples. You will benefit from multidisciplinary supervision, including opportunities for international collaborations. This thesis represents a major scientific challenge with direct industrial applications, offering you valuable experience in the field of nuclear separation and processing technologies.
Monte Carlo methods for sensitivity to geometry parameters in reactor physics
The Monte Carlo method is considered to be the most accurate approach for simulating neutron transport in a reactor core, since it requires no or very few approximations and can easily handle complex geometric shapes (no discretisation is involved). A particular challenge for Monte Carlo simulation in reactor physics applications is to calculate the impact of a small model change: formally, this involves calculating the derivative of an observable with respect to a given parameter. In a Monte-Carlo code, the statistical uncertainty is considerably amplified when calculating a difference between similar values. Consequently, several Monte Carlo techniques have been developed to estimate perturbations directly. However, the question of calculating perturbations induced by a change in reactor geometry remains fundamentally an open problem. The aim of this thesis is to investigate the advantages and shortcomings of existing geometric perturbation methods and to propose new ways of calculating the derivatives of reactor parameters with respect to changes in its geometry. The challenge is twofold. Firstly, it will be necessary to design algorithms that can efficiently calculate the geometric perturbation itself. Secondly, the proposed approaches will have to be adapted to high-performance computing environments.
Sensitivity calculation in deterministic neutronics: development of methodologies for the lattice phase.
Deterministic neutronics calculations usually rely on a two-step approach, called lattice and core steps. In the first one, the multigroup cross-sections are reduced (condensed over a few energy groups and homogenized over assembly-size regions) using a small subset of the whole system geometrical model (typically, a single subassembly representative of a repeated pattern) in order to reduce the dimensionality of the core calculation step. When those reduced cross-section sets are used for core sensitivity analyses, the impact of the lattice step is usually neglected. For some quantities of interest, this can lead to important discrepancies between the computed sensitivities and the actual ones, since lattice transport calculations are key for carrying the fine-energy local neutron spectrum information and resonance self-shielding effects. There can be an additional concern when those sensitivity calculations are used to provide feedback on nuclear data evaluations, or in the case of similarity studies. In order to address this issue, several approaches are available, such as direct calculations or perturbation theory studies, each representing different trade-offs in terms of cost or complexity.
The goal of this PhD is therefore to explore the state of the art of the domain, ranging from the most brute force approach to the ones based on perturbation theory, with the possibility to propose new methodologies. The implementation of the chosen methodologies in new generation codes (such APOLLO3) will allow eventually to improve the accuracy of sensitivity calculation.
The doctoral student will be based in a reactor physics research unit at CEA/IRESNE in Cadarache, which hosts many students and interns. Post-graduation perspectives include research in nuclear R&D labs and industry.