Characterisation of reaction pathways leading to thermal runaway for new battery technologies
The development of all-solid-state cells is no longer a mere hypothesis today. As part of the Safelimove project, we assessed the safety of hybrid polymer cells of 1 Ah and 3 Ah, which led to a publication. Additionally, within the Sublime project, we evaluated the safety of 1 Ah sulfide-based cells (argyrodite), and a publication is currently being submitted.
With the arrival of these new cells, it becomes even more crucial to support their development with a detailed safety assessment and the identification of the complex mechanisms involved. Large-scale instruments such as synchrotrons and neutron reactors offer a powerful opportunity to achieve this goal, as they provide the best spatial and temporal resolutions. For example, thanks to fast X-ray radiography at ESRF, it is possible to visualize the inside of a cell during thermal runaway, thereby identifying the local impact of (electro)chemical reactions on the microstructure of components and validating our thermal runaway models. Moreover, with wide-angle X-ray scattering (WAXS), it is possible to monitor in situ the evolution of the crystalline structure of active materials during a very rapid thermal runaway reaction. Indeed, synchrotron radiation allows the acquisition of one diffractogram every 3 milliseconds. The neutron beam at ILL also enables us to track the evolution of lithium metal structure before, during, and after runaway. It is important to emphasize that these three techniques are currently mastered by the LAPS teams and have already led, or will lead, to publications.
Furthermore, new complementary techniques may be explored, such as studying the impact of thermal/mechanical stress on active materials using the BM32 beamline, or evaluating the oxidation states of metals via X-ray absorption spectroscopy (XAS) on ID26.
More conventional laboratory characterizations will also be carried out, such as DSC, TGA-MS, and XRD.
As part of our various collaborations, for the all-solid-state system, the active material of the positive electrode will most likely be NMC, or even LMFP in the event of supply difficulties. The electrolyte used will be sulphide-based, or even halide-based, while the anode will be composed of lithium metal or even a lithium alloy. If time permits, a post-Na-ion system will be considered from the second year onwards. Among other things, the thesis will aim to identify, based on the materials used, whether there are reactions prior to cathode destabilisation, whether the solid electrolyte reacts with the oxygen in the cathode or with the anode material, and whether these parallel reactions contribute to better or worse cell safety.
The three years of the PhD will be structured as follows: the first year will be dedicated to a literature review and the characterization of sulfide technology. Following the first milestones (1st CSI) and the evaluation of ongoing work on sulfides, the second year will focus either on sodium-ion technology or on further development of sulfide technology. Finally, the third year, in addition to the thesis writing, will concentrate more specifically on the impact of the identified materials on safety.
Modeling of Wall Condensation Phenomena and Liquid Film Interactions
In this thesis, we focus on modeling mass and energy transfer associated with wall condensation in a turbulent flow of a vapor–noncondensable gas mixture. The flow is two-phase and turbulent, where forced, mixed, and natural convection modes may occur. The framework of this work relies on the RANS approach applied to the compressible Navier–Stokes equations, in which wall condensation is described using semi-analytical wall functions developed in a previous doctoral study cite{iziquel2023}. These functions account for the different convection modes as well as suction and species interdiffusion effects, but neglect the presence of a liquid film.
In the literature, the influence of film formation and flow on mass and heat transfer is often neglected, since it is generally assumed that, in the presence of noncondensable gases, the resistance of the gaseous layer to vapor diffusion is much greater than the thermal resistance of the liquid film.
The objective of this thesis is to improve the prediction of heat and mass transfer by investigating, beyond the thermal resistance of the condensate, the dynamic effect of the liquid and its interaction with the gaseous diffusion layer during wall condensation. The study will first consider laminar film flow, and then attempt to extend the analysis to the turbulent regime.
In the gas phase, the wall-function model developed in cite{iziquel2023} for a binary mixture of vapor and a single noncondensable gas will be extended to mixtures of vapor and $n>1$ noncondensable gases (N2, H2, …), in order to address hydrogen risk issues.
The validation of the implemented models will be carried out using results from separate-effect (SET) and coupled-effect (CET) experiments available in the literature (Huhtiniemi cite{huhti89}, COPAIN, ISP47-MISTRA, ISP47-TOSQAN, RIVA). Comparisons at the CFD scale, using wall functions for condensation neglecting the film, will be performed on benchmark cases from the literature and condensation experiments (COPAIN) to assess the impact of this assumption as well as the improvement provided by the new model in terms of accuracy and computational cost.
Modelling of Thermo-Fluid Phenomena in the Plasma Nozzle of the ELIPSE Process
The ELIPSE process (Elimination of Liquids by Plasma Under Water) is an innovative technology dedicated to the mineralization of organic effluents. It is based on the generation of a thermal plasma fully immersed in a water-filled reactor vessel, enabling extremely high temperatures and reactive conditions that promote the complete decomposition of organic compounds.
The proposed PhD research aims to develop a multiphysics numerical model describing the behavior of the process, particularly within the plasma nozzle, a key zone where the high-temperature gas jet from the torch interacts with the injected liquids.
The approach will rely on coupled thermo-aerodynamic modeling, integrating fluid dynamics, heat transfer, phase change phenomena, and turbulence effects. Using Computational Fluid Dynamics (CFD) tools, the study will characterize plasma–liquid interaction mechanisms and optimize the geometry and operating conditions of the process. This modeling will be compared and validated against complementary experimental data obtained from the ELIPSE setup, providing the necessary input for model calibration and validation.
This work will build upon previous research that has led to the development of thermal and hydraulic models of both the plasma torch and the reactor vessel. Integrating the new model within this framework will yield a comprehensive and coherent representation of the ELIPSE process. Such an approach represents a decisive step toward process optimization and industrial scale-up.
The ideal candidate will be a Master’s or final-year engineering student with a background in process engineering and/or numerical simulation, demonstrating a strong interest in physical modeling and computational approaches.
During this PhD, the candidate will develop and strengthen skills in multiphysics numerical modeling, advanced CFD simulation, and thermo-aerodynamic analysis of complex processes. They will also acquire solid experience in waste treatment, a rapidly expanding field with significant industrial and environmental relevance. These skills will provide strong career opportunities in applied research, process engineering, energy, and environmental sectors.
Assessment of new models for the investigation of hypothetical accidents in GEN4 fast reactors.
Multi-component two-phase flows in conjunction with fluid-structure interaction (FSI) problems can occur in a very large variety of engineering applications; amongst them, the hypothetical severe accidents postulated in Generation IV sodium and lead fast-breeder reactors (respectively SFR and LFR).
In SFRs, the worst postulated severe accident is the so-called hypothetical core disruptive accident (HCDA), in which the partial melt of the core of the reactor interacts with the surrounding sodium and creates a high-pressure gas bubble, the expansion of which generates shock waves and is responsible of the motion of liquid sodium, thus eventually damaging internal and surrounding structures.
The LFR presents the advantage that, unlike sodium, lead does not chemically react with air and water and, therefore, is explosion-proof and fire-safe. On the one hand, this allows a steam generator inside the primary coolant. On the other hand, the so-called steam generator tube ruptures (SGTR) should be investigated to guarantee that, in the case of this hypothetical accident the structure integrity is preserved. In the first stage of a SGTR, it is supposed that the steam-generator high-pressure high-temperature water penetrates inside the primary containment, thus generating a BLEVE (boiling liquid expanding vapor explosion) with the same behavior and consequences as the high-pressure gas bubble of a HCDA.
In both HCDA and STGR, there are situations in which the multi-component two-phase flows is in low Mach number regime which, when studied with classical compressible solver, presents problems of loss of accuracy and efficiency. The purpose of this PhD is
* to design a multiphase solver, accurate and robust, to investigate HCDA STGR scenarios.
* to design a low Mach number approach for bubble expansion problem, based on the artificial compressibility method presented in the recent paper "Beccantini et al., Computer and fluids 2024".
The aspect FSI will be also taken into account.
Understanding the signals emitted by moving liquids
Elasticity is one of the oldest physical properties of condensed matter. It is expressed by a constant of proportionality G between the applied stress (s) and the deformation (?): s = G.? (Hooke's law). The absence of resistance to shear deformation (G' = 0) indicates liquid-like behavior (Maxwell model). Long considered specific to solids, shear elasticity has recently been identified in liquids at the submillimeter scale [1].
The identification of liquid shear elasticity (non-zero G') is a promise of discoveries of new liquid properties. For example, do we know that a confined liquid changes temperature under flow? Yet no classical model (Poiseuille, Navier-Stokes, Maxwell) predicts the effect because without long-range correlation between molecules (i.e. without elasticity), the flow is dissipative, therefore athermal. For a change in temperature to be flow induced (without a heat source), the liquid must have elasticity and this elasticity must be stressed [1,2].
The PhD thesis will explore how the mechanical energy of the flow is converted in a thermal response [2]. We will exploit the capacity of conversion to develop a new generation of microfluidic devices (patent FR2206312).
We will also explore the impact of the wetting on the liquid flow, and reciprocally, we will examine how the liquid flow modifies the solid dynamics (THz) of the substrate [3]. Powerful methods only available in Very Large Research Facilities such as the ILL will be used to probe the non-equilibrium state of solid phonons. Finally, we will strengthen our existing collaborations with theoreticians.
The PhD topic is related to wetting, macroscopic thermal effects, phonon dynamics and liquid transport.
1. A. Zaccone, K. Trachenko, “Explaining the low-frequency shear elasticity of confined liquids" PNAS, 117 (2020) 19653–19655. Doi:10.1073/pnas.2010787117
2. E. Kume, P. Baroni, L. Noirez, “Strain-induced violation of temperature uniformity in mesoscale liquids” Sci. Rep. 10 13340 (2020). Doi : 10.1038/s41598-020-69404-1.
3. M. Warburton, J. Ablett, P. Baroni, JP Rueff, L. Paolasini, L. Noirez, “Identification by Inelastic X-Ray scattering of bulk alteration of solid dynamics due to Liquid Wetting”, J. of Molecular Liquids 391 (2023) 123342202
Simulation of flow in centrifugal extractors: the impact of viscous solvents on operation
Within the framework of nuclear spent fuel reprocessing, the CEA co-developed with ROUSSELET-ROBATEL liquid/liquid extraction (ELL) devices aimed at bringing two immiscible liquids into contact, one of which contains the valuable metals to be recovered and the other an extractant molecule. The multi-stage Centrifugal Extractor is one of the devices used to perform ELL at the La Hague plant. The future use of solvents potentially more viscous than current industrial standards may pose performance issues that need to be studied in advance in the laboratory to provide the necessary recommendations to restore the expected performance levels for the plant. The nuclear environment in which these devices operate makes in situ studies nearly impossible, thus depriving R&D of valuable information that is nevertheless essential for a deep understanding of the physicochemical mechanisms at the heart of the issues involved. To address this, the proposed study will rely on a numerical approach that will have been previously validated by comparison with either historical experimental data or data acquired from more recent ad hoc pilot systems. Thus, following a phase of literature review and capitalization of recent measurements, it is proposed to first create test cases that will be used to validate the numerical models. Based on this validation and in light of the knowledge acquired from previous theses concerning the effect of viscosity on flows, it is proposed to numerically explore the impact of an increase in solvent viscosity on centrifugal extractors. This will pave the way for a better understanding of the operation of the devices as well as operational or geometric improvements. The student will work at CEA Marcoule, in a research environment at the crossroads between a team of experimentalists and a team of numerical simulators. This experience will enable the student to acquire important skills in modeling liquid-liquid flows as well as solid knowledge on the development of liquid-liquid contactors.
Multi-physics modelling of a light water nuclear reactor operating under natural convection: study of innovative solutions for startup and power control
Among the most recent designs of water-moderated Small Modular Reactors (SMR), several concepts are characterized by natural convection in the primary circuit during normal and abnormal operation, with the aim of increasing the inherent safety of the design. The absence of primary pumps in this type of SMRs significantly complicates the start-up and power increase ramps. This requires the development of specific start-up procedures to heat up the primary water circuit and enable the reactor to reach its nominal conditions, in accordance with safety requirements. These kinds of procedures rely on simulations using validated models to understand the reactor behavior during these phases and define the accessible parameters domain.
The goal of this PhD project is to develop a numerical model capable of simulating the startup of an SMR operating in natural convection, and to contribute to the validation of this model. The PhD study also aims at developing a methodology for reactor control systems optimization, to attain a fast startup while remaining within the prescribed safety criteria.
The analysis of the reactor startup procedure entails two disciplines: thermal-hydraulics and neutronics, which requires the development of multi-physics coupled simulation tools. Three scientific calculation tools in particular will be coupled in the framework of the PhD study: CATHARE3 (reactor system thermal-hydraulics), FLICA5 (core thermal-hydraulics) and APOLLO3 (neutronics).
The PhD student will work in a team of neutron physicists and thermohydraulic engineers at the IRESNE Institute (CEA Cadarache). He/she will develop skills in nuclear reactor physics and modeling.
Mass transfers and hydrodynamic coupling: experimental investigation and models validation and calibration
With the energy transition and the paramount importance of the nuclear energy in this context, it is pivotal to understand the consequences of potential accident with core meltdown, as well as thinking about mitigation strategy.
During a nuclear severe accident with core meltdown a magma called corium can form a pool in the reactor lower head. The pool is not homogeneous and can stratify into multiple immiscible layers. The composition of the pool may evolve in time, due to progressive material assimilation. With the evolution of the global composition of the corium, the properties of the layers evolve. The vertical position of these layer may then change. This change comes with the creation of droplets from a layer which then cross the other one. The vertical order of the different layers as well as their movements have a significant impact on the heat fluxes imposed on the reactor vessel. A better understanding of these phenomena improves safety of both nowadays and future nuclear reactors.
Modelling work has been done, but it lacks validation and need calibration. Prototypical experiments (with actual materials present inside a reactor) are difficult to carry and are not foreseen in the near future. This PhD aims at experimentally studying the mass transfer between a droplet and its surrounding as well as the droplet creation. The planned experimental setup will use a water-based system which allow for local measurement. The goal is to validate, calibrate the existing model, and potentially create new ones. The final goal being to capitalize the work into PROCOR software platform. The experimental setup will be constructed and operated in LEMTA laboratory in University of Lorraine, where the student will work.
The PhD work will be mainly experimental but will also require software use for calibration, validation and for the design of the experimental setup. This work will be conducted in close collaboration between the laboratories LMAG in CEA/IRESNE (Cadarache) and LEMTA in University of Lorraine (Nancy). The student will work in LEMTA, where the experiments will be conducted, while being part of the CEA. The student will benefit from LEMTA’s expertise in building of experimental setup, transport phenomena in fluids and metrology, and from LMAG’s expertise in mass transfer, physical modeling and simulation in the scope of nuclear severe accidents. The student will regularly interact with CEA team which will follow the work closely. The student will therefore have to regularly go to CEA Cadarache.
The PhD student will be integrated to a dynamic environment comprised of researchers and other PhD students. The PhD candidate needs to be knowledgeable in transport phenomena, and needs to have a taste for experimental sciences.
Radiative heat transfer: efficient numerical resolution of associated problems in Beerian or non-Beerian media for the validation of simplified models
This research proposal focuses on the study, through modeling and numerical simulation, of heat transfer within a heterogeneous medium composed of opaque solids and a transparent or semi-transparent fluid. The considered modes of transfer are radiation and conduction.
Depending on the scale of interest, the radiance is the solution of the Radiative Transfer Equation (RTE). In its classical form, the RTE describes heat transfer phenomena at the so-called local scale, where solids are explicitly represented in the domain. At the mesoscopic scale of an equivalent homogeneous medium, however, the radiance is governed by a generalized RTE (GRTE) when the medium no longer follows the Beer–Lambert law. In this work, we focus on the numerical resolution of the RTE in both configurations, ultimately coupled with the energy conservation equation for temperature.
In deterministic resolution of the RTE, a standard approach for handling the angular variable is the Discrete Ordinates Method (Sn), which relies on quadrature over the unit sphere. For non-Beerian media, solving the GRTE is a very active research topic, with Monte Carlo methods often receiving more attention. Nevertheless, the GRTE can be linked to the generalized transport equation, as formulated in the context of particle transport, and a spectral method can be applied for its deterministic Sn resolution. This is the direction pursued in this PhD project.
The direct application of this work is the numerical simulation of accidents in Light Water Reactors (LWR) with thermal neutrons. Modeling radiative heat transfer is crucial because, in the case of core uncovering and fuel rod drying, radiation becomes a major heat removal mechanism as temperatures rise, alongside gas convection (steam). This topic is also relevant in the context of the nuclear renaissance, with startups developing advanced High Temperature Reactors (HTR) cooled by gas.
The goal of this thesis is the analysis and development of an innovative and efficient numerical method for solving the GRTE (within a high-performance computing environment), coupled with thermal conduction. From an application standpoint, such a method would enable high-fidelity simulations, useful for validating and quantifying the bias of simplified models used in engineering calculations.
Successful completion of this thesis would prepare the student for a research career in high-performance numerical simulation of complex physical problems, beyond nuclear reactor physics alone.
HPC two-phase simulations with lattice Boltzmann methods and adaptative mesh refinement
CEA/STMF develops computational fluid dynamics (CFD) codes in thermohydraulics that aim to quantify mass and energy transfers in nuclear cycle systems such as reactors and management devices of radioactive wastes. This thesis focuses on Lattice Boltzmann Methods (LBM) adapted to Adaptive Mesh Refinement (AMR) inside a generic computing environment based on Kokkos and executable on multi-GPU supercomputers. The proposed work consists in developing LB methods in the Kalypsso-lbm code to simulate coupled partial differential equations (PDEs) modelling incompressible two-phase and multi-component flows such as those encountered in downstream cycle devices. Once the developments have been completed, they will be validated with reference solutions. They will allow a comparison of various interpolation methods between blocks of different sizes in the AMR mesh. A discussion will be held on the refinement and de-refinement criteria that will be generalized for these new PDEs. Finally, benchamrks of performance will quantify the contribution of AMR for 3D simulations when the reference simulation is performed on a static and uniform mesh. This work will use supercomputers which are already operational (e.g., Topaze-A100 from CEA-CCRT), as well as the future exascale supercomputer Alice Recoque depending on the progress of its installation.