Incorporation of U and Pu in nuclear glasses and impact on their long term behavior under water
In order to stabilize its final high-activity waste, the Atalante facility plans to vitrify it on the VESPA platform implemented on the C18 shielded line. The glasses produced will be stored in the short term at the ATALANTE facility and are intended to be sent in the medium term to the French disposal facility, at the Bure site.
The calcination vitrification process of the VESPA platform will aim to produce sodium borosilicate glasses as close as possible to nuclear glasses used at the La Hague plant by Orano. These glasses will have to incorporate higher contents of uranium and plutonium (U and Pu) into their vitreous network than the glasses used industrially until now.
Therefore, to validate the proposed domain of chemical composition of the so-called “Atalante” glasses, the candidate will first have to study the limits of incorporation of U and Pu in UOX type glasses.
Once the chemical domain has been determined, a second part of the PhD thesis will be devoted to the study of the kinetics of alteration of glasses of interest under water and thus examine the impact of U and Pu concentrations on their long-term behavior properties.
The profile of the desired candidate is Master 2 level or equivalent in materials science. He/she must be rigorous, organized and present a strong interest in characterization techniques of solids or liquids as well as for the synthesis of materials. Experience in the glass and/or nuclear field would be a plus. This thesis will offer him/her the opportunity to develop skills in numerous characterization techniques and also experience of work in nuclear facility.
Master 2 materials science.
Modelling of the reactive mixing process for conditioning waste in a concrete matrix
Cementation is currently the preferred method for conditioning a large number of nuclear wastes. Developing a conditioning process requires to master the mixing and blending phases, which will condition the proper dispersion of the waste in the cement matrix and the performance of the final material.
The LNPA is proposing a thesis on the modeling and simulation of the mixing process (mixing of dry fillers, water, waste simulants representative of nuclear waste deposits) to meet the following objectives:
- Simulate the flow of cementitious paste in the mixer and experimentally verify the results obtained
- Optimize process parameters to improve waste dispersion quality
- Predict coating feasibility based on the characteristics of the waste to be conditioned
- Validate transfer from laboratory to industrial scale
A CFD approach is considered: the aim is to describe the evolution of the free surface of the flow, to highlight specific modes such as recirculation and trajectory bifurcation, and finally to describe particle transport with and without coupling to rheology. The simulation results will be evaluated by cross-checking with tests carried out on a conical mixer. This thesis will therefore be the first step in setting up a predictive sizing tool for a cement mixing process applied to the conditioning of nuclear waste.
The candidate, with a background in materials engineering, mechanical engineering or process engineering, will gain experimental experience in process instrumentation and exploitation of results, as well as experience in numerical fluid mechanics and process modelling.
Determination of Phenomenological Law for Simulating Glass Alteration from Microscopic to Macroscopic Scale.
Borosilicate glasses are used to contain long-lived radioactive waste resulting from the reprocessing of spent nuclear fuel. Predicting their long-term behavior in deep geological storage relies on models that describe, in a disjointed manner, the physico-chemical processes from the molecular scale (molecular dynamics) to the macroscopic scale (geochemical model), passing through an intermediate scale known as mesoscopic (Monte Carlo, phase field model, and gel maturation model).
Molecular and mesoscopic scale models deal with simple cases (glasses with 3 or 4 oxides altered in pure water). They have significant explanatory power but limited predictive scope because the actual situation is more complex: nuclear glass consists of about thirty oxides. It undergoes the effects of irradiation and will evolve in an environment influenced by the claystone of the site, iron, corrosion products from metal casings, and the filling material.
The geochemical model allows simulating the behavior of complex glasses under realistic alteration conditions but currently relies on a simplified description of basic processes, sometimes distant from real processes.
The thesis will contribute to bridging the gap between simplified approaches and more realistic complex systems. It focuses on three main axes:
1 - Validation of gel maturation phenomenological laws for glasses of increasing complexity.
2 - Consideration of irradiation effects.
3 - Consideration of environmental effects.
Profile sought: Master's degree (M2) or engineering degree in solid-state physicochemistry/materials science. The thesis will provide the candidate with advanced skills in the field of glasses, modeling, and project management in multidisciplinary research, in collaboration with industrial and academic partners. Numerous employment opportunities are available after the thesis, in the nuclear sector, glass industry, or academia.
Modelisation of HLLW vitrification in cold crucible inductive melter
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
Glass gaskets sealing characterization and modeling for High-temperature steam electrolysis technologies
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.
Predictive modeling of the alteration of nuclear waste containment glass.
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.
We are looking for a student with a master's degree related to modeling or geochemistry, strong Python programming skills, and an interest in understanding processes through models. At the end of these three years, the student will have gained a strong understanding of geochemical modeling (using the CHESS code), mass transfer modeling (using the Hytec code), glass alteration modeling (with the GRAAL2 model), as well as skills in numerical programming in Python. The student will also develop a deep understanding of concepts related to deviation, error, and uncertainty. He will become familiar with issues related to the transfer of pollutants in the environment and nuclear waste management. The knowledge and skills acquired are important in various fields related to material sustainability, the environment, and modeling, including the rigorous methodologies that underlie these approaches.
Physico-chemical coupling between a bubbles population and the oxido-reduction of glass-forming liquid
The calcination-vitrification process is the solution used in France for more than 30 years for the conditioning of high-level nuclear waste resulting from the reprocessing of spent fuel. During the vitrification process, the waste is incorporated into a borosilicate glass-forming liquid at more than 1000°C. The glass-forming liquid is homogenized in temperature and composition by stirring and gas bubbling. The incorporation of waste into glass-forming liquid can also lead to gas releases, including those of oxygen resulting from redox reactions between species dissolved in the liquid. It is important to properly control the impact of these gases on the glass and the process.
The redox state of glass-forming liquid at equilibrium between the dissolved species has been the subject of various studies at the CEA in the context of the vitrification of nuclear waste [1, 2]. On the other hand, few studies have been devoted to the kinetics of gas reactions in glass-forming liquid [3, 4]. The objective of this thesis aims to study and model the impact of gas bubbles, whatever their nature, on the redox of melting and the kinetics of associated reactions. An approach combining experimentation and digital modeling will be adopted.
The desired candidate will have a taste for experimentation, characterization and interpretation of results addressing different scientific fields (physico-chemistry of materials). All experiments will be carried out on non-radioactive elements and will involve processing by digital modeling. This PhD. thesis will allow acquiring valuable professional experience in the glass and nuclear industry.
The Pd-Rh-Ru-Te-O system in nuclear glasses and its impact on the glass melt conductivity
In France, the high-level nuclear waste is vitrified. The components of the waste are integrated in a vitreous borosilicate network and form a homogeneous glass. However, platinum group metals (PGM) Pd, Rh and Ru are very poorly soluble in the glass melt and they form particles, combined or not with oxygen or tellurium.
These PGM particles may modify the physical properties of the glass melt and especially its electrical conductivity wich is paramount for the process control. Hence, the knowledge of the speciation and the morphology of the PGM elements is essential for the control of the vitrification process.
Thereby, this PhD will be split in 2 interdependent approaches: the first one by thermodynamic Calphad calculations and the other one by experimentations. First, the experimental approache will aim to understand and quantify the reduction of (Ru,Rh)O2 and the solubilisation of Ru and Rh in Pd-Te thanks to elaborations and characterizations (SEM-EDS-WDS and XRD mainly) of glasses with PGM particles. The results will complete a Calphad database. Calculations will help to discuss experimental results and will enable to predict the PGM state in the glass melt during the industrial vitrification. Secondly, electrical conductivity measurements at high temperature will be implemented on the glasses previously made to determine the impact of Ru and Rh speciation on the global conductivity of the melt.
A master’s degree or an engineering school diploma in physical chemistry of materials is required for this PhD position. The applicants must be rigorous, autonomous and have good communication and writing skills. Knowledge and experience in the field of glass or thermodynamics would be a plus. This PhD will train the student for research positions and give him/her a wide range of skills in thermodynamics and physical properties of glasses and metals.
Automatic reverse-engineering of BIM models using Machine Learning
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.
Development of methodologies for testing electronic systems in irradiating environments
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.
System-level testing and the use of commercial components (COTS) in irradiating environments are topical issues. At the end of the thesis, the student will be able to apply these skills to a wide range of applications in the nuclear field (A&D sites, reactors), as well as to large particle physics instruments and the space sector.
Candidate profile : Master's degree in electronics or engineering degree in electronics.