Bottom-up study of Ionic Transport in Unsaturated Hierarchical Nanoporous Materials : application to cement-based materials
Ion transport is critical in determining the durability of cement-based materials and, therefore, the extension of service life of concrete (infra)structures. Transport phenomena determine the containment capacity of concrete, which is crucial in the design and asset management of concrete infrastructures for energy production. Under most service conditions, concrete exists in unsaturated conditions. Anomalous transport has been associated with cement-based materials, and the reasons behind such deviations from the expected behavior of other porous materials may stem from nanoscale processes.
Research efforts have aimed to correlating material composition and microstructure to transport properties and durability. However, to date, the majority of predictive modeling of durability does not explicitly account for nanoscale processes, which are fundamental in determining transport properties. Recent advances have been made in quantifying the behavior of confined water in various phases present in cement systems. Calcium silicate hydrates (C-S-H) are the main hydrated phase in cement-based materials and present nanopores in the micro and mesopore range. The effects of desaturation remain however to be fully worked out. A fundamental understanding of transport processes requires a multiscale framework in which information from the molecular scale reverberates across other relevant scales (in particular, the mesoscale associated with C-S-H gel porosity (~nm), capillary porosity, and interfacial transition zone (~µm) up to the macroscopic scale of industrial application in cement-based materials).
The goal of this PhD work is to evaluate the ionic transport of chlorides, a critical species for the durability of concrete, under non-saturated conditions by combining small-scale simulations, multiscale modelling and experimentation in a bottom-up approach. The work will focus on the C-S-H. The project aims to characterize the effects of desaturation on the nanoscale processes driving transport of chlorides.
Design and optimization of an innovative breeding blanket concept for a compact high heat flux nuclear fusion reactor
Skills:
Technical: heat transfer, structural mechanics, hydraulics, materials, numerical simulation
Non-technical: writing, interpersonal skills, English
Prerequisites: this thesis will be preceded by a 6-month internship. Contact the supervisor for more details about the topic.
Context:
This PhD focuses on the design and optimization of an innovative breeding blanket for compact nuclear fusion reactors. Nuclear fusion offers a promising solution to produce clean and sustainable energy. However, it requires the continuous production of tritium, a rare isotope, through breeding blankets surrounding the plasma. These blankets must also extract the generated heat. In compact reactors, technical constraints are increased due to extremely high heat fluxes and severe thermal and neutron conditions.
The PhD will take place within the Design, Calculations, and Realizations Office at CEA Saclay, a recognized player in the development of breeding blankets at the European level. This office has designed several concepts, such as HCLL (Helium Cooled Lithium Lead) and BCMS (Breeder and Coolant Molten Salt), two types of blankets based on helium or molten salt cooling systems.
PhD description:
The research program will take place over three years. The first year will focus on studying existing blankets, identifying the constraints of compact reactors, selecting appropriate materials and heat transfer fluids, and developing a preliminary design of the blanket. The following years will be dedicated to multiphysics modelling (thermal, mechanical, neutron), followed by iterative optimization of the concept to improve its performance.
Perspectives:
The results of this PhD will have a significant impact on the development of compact fusion reactors by ensuring tritium production and structural integrity. This work could also open new avenues for future research on even more advanced breeding blankets, contributing to the growth of sustainable and commercially viable fusion energy.
Seismic analysis of the soil-foundation interface: physical and numerical modelling of global tilting and local detachment
Rocking foundations offer a potential mechanism for improving seismic performance by allowing controlled uplift and settlement, but uncertainties in soil-foundation interactions limit their widespread use. Current models require complex numerical simulations, which lack accurate representation of the soil-foundation interface.
The main objective of this thesis is to model the transition from local effects (friction, uplift) to the global response of the structure (rocking, sliding, and settlement) under seismic loads, using a combined experimental and numerical approach. Hence, ensure reliable numerical modeling of rocking structures. Key goals include:
• Investigating sensitivity of physical parameters in seismic response of rocking soil-structure systems using machine learning and numerical analysis.
• Developing and conducting both monotonic and dynamic experimental tests to measure the soil-foundation-structure responses in rocking condition.
• Implementing numerical simulations to account for local interaction effects and validate results with experimental results.
Finally, this research aims to propose a reliable experimental and numerical framework for enhancing seismic resilience in engineering design. This thesis will provide the student with practical engineering, along with expertise in laboratory tests and numerical modeling. The results will be published in international and national journals and presented at conferences, advancing research in the soil and structure dynamics field.
Study of of the thermodynamic of K2CO3-CO2-H2O for the development of NET and SAF technologies
.Bioenergy with Carbon Capture and Storage (BECCS) uses biomass energy while capturing the carbon dioxide released by the process, resulting in negative emissions into the atmosphere. The reference process in Europe uses potassium carbonate but at atmospheric pressure [1], whereas its sequestration or hydrogenation into sustainable molecules requires high pressures.
The thesis consists in acquiring new thermodynamic and thermo-chemical data at high temperature/pressure [2] required for the energy optimization of such a process, and integrating them into a thermodynamic model.
The overall process will then be reassembled in order to quantify the expected energy gain.
The thesis will be carried out at the Thermodynamic Modeling and Thermochemistry Laboratory (LM2T), in collaboration with LC2R (DRMP/SPC) for the experimental part.
References :
[1]K. Gustafsson, R. Sadegh-Vaziri, S. Grönkvist, F. Levihn et C. Sundberg, «BECCS with combined heat and power: assessing the energy penalty,» Int. J. Greenhouse Gas Control, vol. 110, p. 103434, 2021.
[2] S. Zhang, X. Ye et Y. Lu, «Development of a Potassium Carbonate-based Absorption Process with Crystallization-enabled High-pressure Stripping for CO2 Capture: Vapor–liquid Equilibrium Behavior and CO2 Stripping Performance of Carbonate/Bicarbonate,» Energy Procedia, 2014
Experimental and numerical analysis of fluid-structure interactions in the propagation of rarefaction waves through complex structures in pressurized water reactors
Loss of coolant accident (LOCA) in pressurized water reactors (PWR) leads to fast transient phenomena, such as the propagation of rarefaction waves within the reactor's internal structures. These waves generate transient pressure loads between different areas, such as the reactor core and the bypass zone, which places stress on the baffle. The deformation of this critical structure can compromise the structural integrity of the reactor and complicate the handling of fuel assemblies, particularly their removal after the accident.
The main scientific objective is to develop, implement, and validate new numerical models that allow for a more accurate simulation of rarefaction wave propagation through complex obstacles. The current state of the art relies on simplified models, validated only for simple configurations such as single-orifice plates. However, there is a need to extend these models to more complex geometries, such as plates with multiple holes, using different numerical methods.
The development of a porosity model to represent fuel assemblies is also crucial. The expected results will be validated experimentally and have direct applications for industrial partners EDF and Framatome, enhancing the industrial relevance of this research.
The thesis will adopt a combined approach, both experimental and numerical. The use of the MADMAX platform will allow for the testing of various complex obstacles and the collection of detailed experimental data using specialized sensors. This data will be used to validate the numerical models developed in the EUROPLEXUS software. Additionally, the simulations will include innovative approaches such as a new porosity model for the internal structures of the reactors. Participation in international conferences and publication of results are planned to ensure the scientific dissemination of the findings.
The thesis will be conducted at the DYN laboratory of CEA Paris-Saclay, equipped with unique experimental facilities, such as the MADMAX platform, and has strong expertise in numerical modeling. Several industrial (EDF, Framatome) and academic collaborations will provide a rich environment for the doctoral candidate, with regular exchanges within international networks.
The ideal candidate should possess solid skills in fluid mechanics, structural dynamics, numerical modeling (finite element, finite volume), and programming. Previous experience with tools like EUROPLEXUS will be a plus. An M2 internship may be offered to familiarize the candidate with the methods and tools used in this thesis.
This thesis will enable the doctoral candidate to acquire highly specialized skills in fluid-structure interactions, numerical modeling, and experimentation in an industrial context. These skills are in high demand in the energy, aerospace, and advanced simulation technology sectors, paving the way for careers in applied research or engineering within the industry.
Modeling and experimental validation of a catalytic reactor and optimization of the process for the production of e-Biofuels
During the past 20 years, « Biomass-to-liquid » processes have considerably grown. They aim at producing a large range of fuels (gasoline, kerozene, diesel, marine diesel oil) by coupling a biomass gazéification into syngaz unit (CO+CO2+H2 mixture) and a Fischer-Tropsch (FT) synthesis unit. Many demonstration pilots have been operated within Europe. Nevertheless, the low H/C ratio of bio-based syngaz from gasification requires the recycling of a huge quantity of CO2 at the inlet of gaseification process, which implies complex separation and has a negative impact on the overall valorization of biobased carbon. Moreover, the possibility to realize, in the same reactor, the Reverse Water Gas Shift (RWGS) and Fischer-Tropsch (FT) reaction in the same reactor with promoted iron supported catalysts has been proved (Riedel et al. 1999) and validated in the frame of a CEA project (Panzone, 2019).
Therefore, this concept coupled with the production of hydrogen from renewable electricity opens new opportunities to better valorize the carbon content of biomass.
The PhD is based on the coupled RWGS+FT synthesis in the same catalytic reactor. On the one hand a kinetic model will be developed and implemented in a multi-scale reactor model together with hydrodynamic and thermal phenomena. The model will be validated against experimental data and innovative design will be proposed and simulated. On the other hand, the overall PBtL process will be optimized in order to assess the potential of such a process.
Study and simulation of phase entrainment in mixer-settler batteries
As part of the development of new liquid-liquid extraction separation processes, experimental tests are implemented to demonstrate the recovery of valuable elements sufficiently decontaminated from impurities. These tests are commonly carried out in mixer-settler batteries. However, depending on the operating conditions, these finished products may be contaminated by impurities. This contamination results from the combination of several factors:
-Hydrodynamic: Entrainment in the solvent of non-decanted aqueous drops containing impurities
-Chemical: the impurity separation factor is low (less than 10-3)
-Process: the entrainment of drops is amplified with the increase in the rate (reduction of the residence time of the drops)
This thesis aims to increase the understanding of the different phenomena responsible for these phase entrainments in order to estimate optimal operating parameters and to guarantee a contamination of the finished products below a fixed threshold. The aim will be to develop a macroscopic model to predict the flow rate of non-decanted droplets as a function of the operating conditions in the mixer-settler batteries. It will have to be based on hydrodynamic simulations coupling the resolution of a droplet population balance to a continuous phase flow. A coupling will be carried out between this hydrodynamic model and the PAREX or PAREX+ code to size the process diagrams. The qualification of the proposed models will have to be done by comparisons with experimental measurements (based on previous or future test campaigns).
Methodology for studying the deployment of a fleet of innovative nuclear reactors driven by grid needs and constraints
Power grids are to a society what the blood system is to the human body: the providers of electrical energy essential to the daily life of all the organs of society. They are highly complex systems that have to ensure balance at all times between consumer demand and the power injected onto its lines, via mechanisms on different spatial and temporal scales.
The aim of this thesis is to develop a methodology for optimizing the deployment of innovative nuclear reactors in power grids, adapted to their specific needs and constraints. This approach should be applicable to a wide variety of grids, from island to continental scale, and to various levels of penetration and technologies of Variable Renewable Energies (VREs). Network constraints will need to reflect stability requirements in the short term (location and capacity of inertial reserves, participation in ancillary services), medium term (controllability and load following), and long term (seasonal availability and load factor of generation resources). Innovative nuclear reactors can be of any technology, and are characterized by macroscopic parameters such as load ramp-up/down kinetics, partial power levels, time before restart, cogeneration capacities, etc., as well as the technical and economic data required for dispatching. The aim is then to be able to draw up a profile (i.e. location, power, kinetics) of nuclear reactor fleets guaranteeing stabilized operation of power grids despite a high VREs penetration rate. Two main contributions are expected:
- Academic contribution: to propose an innovative methodology for optimizing the deployment of large-scale energy systems comprising innovative nuclear reactors, by integrating both the physics of power grids and their operational constraints;
- Industrial contribution: develop recommendations for the optimal deployment of innovative nuclear reactors in power systems incorporating VREs, taking into account aspects such as reactor power and inertia, location, reserve requirements for system services, load-following capability and availability.
The PhD student will be based in an innovative nuclear systems research unit. At the intersection of the study of nuclear reactor dynamics, power system physics and optimization, this energetics thesis will offer the PhD student the opportunity to develop in-depth knowledge of tomorrow's energy systems and the issues associated with them.
Modeling of complexation equilibria of actinides in nitric medium. Application to the PUREX process
The PAREX+ code is a major tool in the field of separation chemistry. It allows for the modelling and simulation of separation processes base on solvent extraction. In this code, the distribution of interest species between the aqueous and organic phases is calculated at every point in the process, both in steady and transitory states. The aim of this thesis is to improve this distribution model. To achieve this, a better understanding of the phenomena involved in the organic and aqueous phases is necessary, as well as a new approach to incorporate them into the model. This thesis thus combines experimental work and modeling. The student will join a supervisory team composed of experts in separation chemistry and modeling. His work will be valued through the publication of papers and participation in international conferences. At the end of this thesis, the student will have solid knowledge in the field of solvent extraction and its modeling, which he can leverage with industry or research organizations in the nuclear field or in other areas of separation chemistry (separation of rare earths or hydrometallurgy).
Characterisation of the gaseous leak at the contact interface between rough surfaces during loading and unloading - application to the case of metal seals
In various industrial applications, fully metallic seals are employed to guarantee a high level of sealing of mechanical assemblies under severe thermodynamics conditions. Their performance is entirely controlled by the mechanical behaviour of the contacting interface between the facing rough surfaces of the seal and the flange, similar to a fracture, anisotropic and multi-scale by nature. The objective of the thesis is to improve our comprehension and predicting capabilities of the sealing mechanisms of gases in a rough fracture using a numerical approach coupled with experiments.
The work takes place in the continuity of previous studies performed at the laboratory. It will focus first on the conception of an experimental apparatus that will be used to press two metallic rough surfaces against each other with a given force, having the possibility to measure the corresponding leakage rate as well. The experiments will be performed during loading and unloading of the contact to characterise the hysteresis phenomenon brought by the permanent deformation of the sealing material at first loading. The results obtained will be compared to numerical ones in various configurations using models developed at the laboratory, in order to validate these latter. By experience, it is known that the flow simulation gives satisfactory results, but discrepancies persist in the contact mechanics model. Thus, it should be improved regarding the plastic effects specifically encountered in contact, considering the finite thickness of the sealing liner and optimizing the computational cost. Afterwards, the preceding results will be transposed to the industrial case of the HELICOFLEX metal seal, using a two-scale modelling strategy, coupling the macroscopic information at the seal scale to the microscopic one at the roughness scale.