Modelling/Simulation of the synthesis of anti-corrosion coatings using the MOCVD process for low-carbon energy production
The durability of materials used in many areas of energy production is limited by their degradation in the operating environment, which is often oxidising and at high temperature. This is particularly true of High Temperature Electrolysers (HTE) for the production of ‘green’ hydrogen, or the fuel cladding used in nuclear reactors to produce electricity. Anti-corrosion coatings can/should be applied to improve the lifespan of these installations, thereby conserving resources. A process for synthesising coatings using a reactive vapour route with liquid organometallic precursors (DLI - MOCVD) appears to be a very promising process.
The aim of this thesis is to model and simulate the DLI-MOCVD coating synthesis process for the two applications proposed above. Simulation results (deposition rate, deposit composition, spatial homogeneity) will be compared with experimental results from large-scale ‘pilot’ reactors at the CEA in order to optimise the model's input parameters. On the basis of this CFD simulation/experiments dialogue, the optimum conditions for deposition on a scale 1 component will be proposed. A coupling between CFD simulations and Machine Learning will be developed to accelerate the change of scale and the optimisation of scale 1 deposits.
Implicit/explicit transition for numerical simulation of Fluid-Structure Interaction problems treated by immersed boundary techniques
In many industrial sectors, rapid transient phenomena are involved in accident scenarios. An example in the nuclear industry is the Loss of Primary Coolant Accident, in which an expansion wave propagates through the primary circuit of a Pressurized Water Reactor, potentially vaporizing the primary fluid and causing structural damage. Nowadays, the simulation of these fast transient phenomena relies mainly on "explicit" time integration algorithms, as they enable robust and efficient treatment of these problems, which are generally highly non-linear. Unfortunately, because of the stability constraints imposed on time steps, these approaches struggle to calculate steady-state regimes. Faced with this difficulty, in many cases, the kinematic quantities and internal stresses of the steady state of the system under consideration at the time of occurrence of the simulated transient phenomenon are neglected.
Furthermore, the applications in question involve solid structures interacting with the fluid, undergoing large-scale deformation and possibly fragmenting. A immersed boundary technique known as MBM (Mediating Body Method [1]) recently developed at the CEA enables structures with complex geometries and/or undergoing large deformations to be processed efficiently and robustly. However, this coupling between fluid and solid structure has only been considered in the context of "fast" transient phenomena treated by "explicit" time integrators.
The final objective of the proposed thesis is to carry out a nominal regime calculation followed by a transient calculation in a context of fluid/immersed-structure interaction. The transient phase of the calculation is necessarily based on "explicit" time integration and involves the MBM fluid/structure interaction technique. In order to minimize numerical disturbances during the transition between nominal and transient regimes, the calculation of the nominal regime should be based on the same numerical model as the transient calculation, and therefore also rely on an adaptation of the MBM method.
Recent work defined an efficient and robust strategy for calculating steady states for compressible flows, based on "implicit" time integration. However, although generic, this approach has so far only been tested in the case of perfect gases, and in the absence of viscosity.
On the basis of this initial work, the main technical challenges of this thesis are 1) to validate and possibly adapt the methodology for more complex fluids (in particular water), 2) to introduce and adapt the MBM method for fluid-structure interaction in this steady-state calculation strategy, 3) to introduce fluid viscosity, in particular within the framework of the MBM method initially developed for non-viscous fluids. At the end of this work, implicit/explicit transition demonstration calculations with fluid-structure interaction will be implemented and analyzed.
An internship can be arranged in preparation for thesis work, depending on the candidate's wishes.
[1] Jamond, O., & Beccantini, A. (2019). An embedded boundary method for an inviscid compressible flow coupled to deformable thin structures: The mediating body method. International Journal for Numerical Methods in Engineering, 119(5), 305-333.
Improving phase field damage models - Application to vitroceramic materials subjected to self-irradiation
The vitrification of nuclear waste is a solution currently adopted for the storage of nuclear waste. The vitroceramic materials considered for this application consist of a glass matrix and inclusions of crystalline phases. Rich in radioactive elements, these inclusions undergo self-irradiation resulting in their swelling, which may cause cracking of the glass matrix. It is necessary to know the maximum amount of inclusions below which the material does not crack. An experimental study on radioactive materials, produced and monitored over time, is excessively expensive and the development of a numerical approach could make it possible to better target the materials to be studied.
Following Gérald Feugueur's thesis work on the subject, which highlighted the difficulty of current models in dissociating crack initiation and propagation, the main goal is to develop and test an improved phase field model incorporating an elasticity-independent crack nucleation criterion, based on regularized models of softening plasticity. The model will be implemented using the finite element method (FEniCS code) and an alternative method using Fourier transforms (AMITEX code). Following cross-validation, the most efficient implementation will be selected for application to large-scale 3D microstructures. Close exchanges with CEA Marcoule will enable us to characterize the microstructure of the materials, and an experiment currently underway should enable us to analyze the potential cracking of these materials under self-irradiation.
Compréhension et modélisation du transport des gaz dans un combustible UO2 présentant plusieurs familles de porosités
Sans objet (candidats français uniquement pour cette thèse)
Development of highly reactive bio-based polyhydroxyurethanes for the substitution of isocyanates in polyurethanes
Polyurethanes are thermosetting materials with significant environmental impacts. They are primarily synthesized from isocyanates, which are highly hazardous substances (toxic, sensitizing, and some even classified as CMR - Carcinogenic, Mutagenic, or Reprotoxic) and are subject to REACH restrictions. In this context, polyhydroxyurethanes (PHUs) offer several advantages: (i) they are more easily bio-based compared to conventional PUs, (ii) their synthesis does not involve isocyanates, but (iii) instead allows for CO2 sequestration. However, the precursors used in the synthesis of PHUs (cyclic carbonates and amines) exhibit much lower reactivity than isocyanates, resulting in curing times that are currently incompatible with the temperatures and production rates required for this type of material.
Several research directions have been proposed to optimize PHU curing kinetics, focusing on the identification of (i) new cyclic carbonate and amine precursors chemically substituted at the a or ß positions of the reactive group, and (ii) new high-performance catalysts capable of activating both types of precursors used in synthesis.
In this context, the PhD candidate will be tasked with synthesizing new cyclic carbonate and amine precursors and studying their reactivity to identify the most favorable conditions for the synthesis of highly reactive PHUs. The results obtained during this work will then be analyzed using symbolic Artificial Intelligence models developed at CEA.
This PhD project is part of the PHURIOUS project, funded by the PEPR DIADEM program, which aims to integrate high-throughput synthesis and characterization techniques in polymer chemistry with digital tools, including DFT calculations, molecular dynamics simulations AI approaches.
Development of a multi-criteria comparison tool for electrochemical stationary storage systems
Use of stationary storage systems is now essential to keep pace with changes in the electricity grid and the growing integration of intermittent renewable energies such as solar and wind power. The choice of a storage solution is based on a number of criteria, including performance, lifetime, environmental impact, safety, regulatory constraints and, of course, economics.
The laboratory possesses comparative data on these different criteria, via experimental studies and feedback on existing systems. In addition, an initial software tool has been developed to assess environmental impact using LCA (Life Cycle Assessment). The aim of this thesis work is to integrate these different components into a broader comparison tool with a multi-criteria approach, targeting specific case studies and a limited number of storage technologies that have reached sufficient maturity for the available data to be reliable.
High yield strength austenitic stainless steels for nuclear applications: numerical design and experimental study
The PhD thesis is part of a project that aims at designing new austenitic stainless steels grades for nuclear applications, which are specifically suitable to in-service conditions encountered by the components and to the manufacturing process. More precisely, the subject deals with bolt steels achieved by controlled nitriding of powders which are then densified by hot isostatic pressing. Indeed, current bolt steel grades may suffer from stress corrosion cracking, while nitriding allows to increase the chromium content, which is beneficial from that point of view.
The study will start by the definition of specifications and associated criteria, then CALPHAD calculations in the Fe-Cr-Ni-Mo-X-N-C system will be done to define promising compositions. Then, selected compositions will be supplied as powders. The behaviour of powders during nitriding will be studied and modelled. Samples will be nitrided, densified and heat treated. One grade will be then selected and fully characterised: mechanical properties and deformation mechanisms, corrosion behaviour. One important objective is to demonstrate the advantages of the new grade compared to the industrial solution.
Turbulence synthesization methods for hybrid URANS/LES CFD approaches in multi-scale simulation of nuclear cores
Problem description: Fluid-structure interactions in nuclear reactor cores are a result of mechanisms occurring at different space scales. The component scale represents the global flow inside the core and is generally simulated though porous media methods. The local scale represents the fuel assembly: it requires CFD scale-resolving methods to calculate consistent fluid forces on the structures, and it features a certain degree of fluid-structure coupling. With the goal of performing multi-scale simulations of a core, the local scale requires the generation of boundary conditions from the component scale. This can be achieved only by a synthetic generation of turbulence, based on the flow results at the component scale. However, the porous media approach used at the component scale does not contain details on the turbulent quantities: the development of new numerical methods is required for generating consistent synthetic turbulence in this configuration.
Objectives:
1. Identify proper hybrid URANS/LES approaches for fuel assembly vibration related issues
2. Identify available turbulence parameters in porous media methods and explore bottom-up scaling approaches
3. Develop a turbulence synthesization method applicable to any fuel array inside a core
Expected results:
1. A novel approach for fluid-induced vibration analysis based on a multi-scale method
2. Clarify the key parameters to generate proper turbulence-resolved boundary conditions in the specific configuration studied
3. Validate the new methods on available experimental configurations
Validation of new APOLLO3 neutron transport calculation models for Light Water Reactors using multigroup Monte Carlo simulations combined with a perturbative approach
For the past twelve years, CEA has been developing a deterministic multi-purpose neutron transport code, APOLLO3, which is starting to be used for reactor studies. A classical two-step APOLLO3 calculation scheme is based on a first stage of two-dimensional infinite lattice calculations in fine transport, generating multi-parameter cross-section libraries used in the second stage of 3D core calculations. In the case of a large power reactor, the core calculation requires approximations that can differ in accuracy, depending on the type of application.
The reference calculation schemes of the SHEM-MOC type and the industrial schemes of the REL2005 type, still in use at the lattice stage by CEA and its industrial partners, EDF and Framatome, were developed in the mid-2000s, based on the methods available in the APOLLO2.8 code. Since then, new methods have been implemented in the APOLLO3 code, which have been individually verified and validated, demonstrating their ability to improve the quality of results at the lattice stage. These include new self-shielding methods, subgroups and Tone, the use of surface line sources in flux calculations using the method of characteristics, flux reconstruction for burnup calculations and a new 383-group fine energy mesh.
The aim of this thesis is to define and validate two new lattice calculation schemes for LWR applications to be used in future calculation tools at CEA and its partners. The goal is to integrate all or part of the new calculation methods, while aiming for reasonable calculation times for the reference scheme, and compatible with fast-running routine usage for the industrial scheme. The calculation schemes implemented will be validated in 2D on geometries taken from the VERA benchmark. Validation will be carried out using an innovative approach involving continuous-energy or multi-group Monte Carlo calculations and a perturbation analysis.
Designing a fast reactor burnup credit validation experiment in the JHR reactor
The primary mission of the Jules Horowitz experimental nuclear Reactor (JHR) is to meet the irradiation needs of materials and fuels for the current nuclear industry and future generations. It is expected to start around 2032. The design of the first wave of experimental devices for RJH already includes specifications for GEN2 and 3 industrial constraints. On the other hand, the field of experiments essential to GEN4 Fast Breeder Reactor remains quite open in the longer term, while no fast-spectrum irradiation facility is currently available.
The objective of this thesis is to study the feasibility of integral experiments in the JHR or another light water reactor, for validation of the reactivity loss with innovative FBR fuels.
In the first part of this thesis, fission products (FPs) that contribute to the loss of reactivity in a typical FBR will be identified and ranked by importance. The second part is the activation measurement and evaluation of the capture cross section of stable FPs in a fast spectrum. It involves the design, specification, implementation and achievement of a “stable” FBR-FP target in the ILL reactor or in the CABRI reactor fuel recovery station (potentially with thermal neutron shields). The third and final part is the design of an experiment in the JHR to generate and characterize FBR FPs. This experiment should be sufficiently representative of fuel irradiation conditions in a FBR. The goal is to access the FP inventory by underwater spectrometry in the JHR and integral reactivity weighing before/after irradiation in CABRI or another available facility.
The thesis will be carried out in a team experienced in the physics and thermal-hydraulics characterization of the JHR. The candidate will be advised by several experts based in the department. The candidate will have the opportunity to promote his/her results before the nuclear industry partners (CEA, EDF, Framatome, Orano, Technicatome etc.).