Thermodynamic study of the Nb-O-Zr system for the nuclear fuel elements recycling
The first step of nuclear material recycling consists in a section-cutting process of the fuel assemblies leading to shells.
Nuclear materials in the cut sections are dissolved in acid solutions whilst structural as well as cladding materials are rinsed and then compacted in CSD-C containers for a final storage in CIGEO.
The REGAIN project aims at studying the feasibility of an alternative solution: the objective is to investigate the possibility to optimize the nuclear and cladding materials management by reducing the radiological source term. The idea is to proceed to a sequence of decontamination steps in order to minimize the waste volume: The first step consists in removing minor actinides and fission products and the second one in the separation of zirconium from structural activation products.
In order to feed the industrial process study, a part of the REGAIN project aims at collecting raw data, which will be used by the other work packages of the project.
In this framework, CEA proposes a post-doctoral position with the purpose of developing a thermodynamic database for the Nb-O-Zr system starting from literature data as well as using experimental informations obtained within the first stages of the project. It will be also possible to include a selection of key fission products into the existing database. The candidate may also be asked to complete the existing data by an experimental campaign to obtain a complete set of data for the modelling. The scientific approach will be based on the CALPHAD method: this method allows developing a thermodynamic database by the definition of an analytical formulation of the thermodynamic potential, which will be used to calculate phase diagrams as well as thermodynamic properties of multi-components systems.
Separation microsystem coupled to mass spectrometry for on-line purification and characterisation of nuclear samples
The miniaturisation of analytical steps commonly carried out in laboratories offers many advantages and particularly in the nuclear sector, where the reduction of material consumption and waste production is of major interest. In this context, one of our laboratory’s focus area is the miniaturisation of analytical tools, particularly chromatographic separation techniques. The aim of this project is to reduce the scale of the purification steps of nuclear samples by solid phase extraction chromatography, prior to the analytical processes. Obtaining these miniaturised extraction devices is based on the in situ synthesis and anchoring of monoliths, in the channels of cyclic olefin copolymer (COC) microsystems. Since this material is chemically inert, COC functionalisation strategies are currently under development to covalently graft reactive sites on its surface, before locally anchoring actinide-specific monoliths in the micro-channels. The aim is to design and fabricate chromatographic extraction microsystems in COC, and to implement them for chemical purification and mass spectrometry measurements, both off-line and on-line.
Development of a simulation tool for the pitting process of a stainless steel used for the storage of nuclear waste
Structural nuclear waste is compacted in patties, stacked in a stainless steel container. In these compacting boxes are placed various metal-type materials with the addition of organic matter, including chlorinated waste. By radiolytic degradation, these can lead to the formation of hydrogen chloride HCl. During the storage phase, relative humidity may be present within the container, which, added to the HCl, may lead to a phenomenon of condensation, resulting, on the surface of the materials, of acid and concentrated into chloride ions condensates. In contact with this acid and chloride electrolyte, a pitting phenomenon is likely to begin on the surface of a stainless steel. This is a local phenomenon that can lead to the piercing of the material in extreme cases. The initiation of this phenomenon depends on several factors: the morphology of the electrolyte, its composition and its evolution over time.
If nowadays this phenomenon is well known, modeling it remains a major challenge because it is a coupled multi-physics and multi-parameter problem. Many questions remain open, particularly at the level of the physical and chemical laws to be used or how to represent the corrosion process?
The objective of the post-doctorate is to develop a tool under COMSOL capable of simulating the initiation and the evolution over time of a pit on the surface of a stainless steel. The approach will be based on a mechanistic modeling of the processes (material transport process and all the chemical and electrochemical reactions).
The post-doctorate will take place in several actions:
1- make a state of the art of the bibliography in order to understand the pitting phenomenon and to identify the laws necessary for modeling.
2-simulate the spread of the pit in a chloride environment in order to establish a propagation criterion.
3-the pitting initiation will be implemented in order to obtain a complete tool capable of simulating the pitting process
Postdoc in Multi-instrumented operando monitoring of Li-ion battery for ageing
Nowadays, the development of new battery technology requires increasing the knowledge of degradation mechanisms occur inside the cell and monitor the key parameter in real time during cycling to increase the performances, lifetime and safety of the cells. To achieve these goals development of new sensing technology and integration inside and outside the cell is needed. The goal of the SENSIGA project is used advanced sensing technology to improve the monitoring of the cell by acquiring useful data correlate to the degradation process and develop more efficient battery management system with accurate state estimators. SENSIGA is a part of PEPR Batteries lead by CNRS and CEA and funding by the French Research Programme FRANCE 2030 to accelerate the development of new battery technology.
You will have the opportunity to work in a stimulating scientific environment focusing on the characterisation of both state of the art and latest generations of battery materials. Based on the sensing technology developed at CEA and from the state of the art, the SENSIGA project will reach the objective of the BATTERY2030+ roadmap goals for smart cells (https://battery2030.eu/research/roadmap/). One of the objectives of the project is to use external sensors to monitor the key parameters of the cell related to performances, ageing and safety behaviours.
Earthquake effect on underground facilities
The Industrial Centre for Geological Disposal (Cigeo) is a project for a deep geological disposal facility for radioactive waste to be built in France. These wastes will be put in sealed packages in tunnels designed at 500 meters depth. The seals are made of a bentonite/sand mixture which has a high swelling capacity and a low water permeability. As a part of the long-term safety demonstration of the repository, it must be demonstrated that the sealing structures can fulfill their functions under seismic loads over their entire lifetime. In order to guarantee this future nuclear waste repository, CEA and Andra are collaborating to work on the potential scientific and engineering challenges involved.
The responses of underground repository to earthquake events are complex due to the spatially and temporally evolving hydro-mechanical properties of the surrounding media and the structure itself. Accurate modeling of the behavior, therefore, requires a coupled multiphysics numerical code to efficiently model the seismic responses for these underground repositories within their estimated lifespan of 100 thousand years.
The research will therefore, propose a performance assessment for sequential and parallel finite element numerical modeling for earthquake analysis of deep underground facilities. Then perform a synthetic data sampling to account for material uncertainties and based on the obtained results in the previous assessment, run a sensitivity analysis using a FEM or a metamodeling process. Finally, the results and knowledge gained within the span of this project will be processed and interpreted to provide responses for industrial needs.
Experimental and technological developments of a process for the mineralization of organic liquid waste by plasma
The ELIPSE process developed at the CEA allows the destruction of organic liquids by injection into a high-power plasma.
If the feasibility of destroying different organic components at flow rates of a few liters per hour has now been demonstrated, tests must now be further developed for reference organic liquids appropriately chosen according to existing deposits.
These studies, based on the characterization data of the chosen LORs, will aim to provide detailed process results obtained with the most representative operating conditions, to allow a complete and quantitative evaluation of the process. This will make it possible to establish operating, robustness and endurance data for the process.
This work will include the study of the behavior of radioelements in the process, which will be essential for the nuclearization study: this will involve studying the physico-chemical behavior of actinides during their processing via the use of inactive simulants.
Aqueous alteration of nuclear glass in its disposal environment
Exploitation, characterization and modeling of so-called "integral" experiments of glass alteration intended for the confinement of nuclear waste (SON68 and AVM4) in the presence of iron, cementitious material and argillite from the Bure site in two geometrical configurations: one simulating a disposal cell, the other intimately mixing the materials present. These tests were launched on behalf of ANDRA between 2017 and 2018 and their characterization started in the past two years.
Calculation of the thermal conductivity of UO2 fuel and the influence of irradiation defects
Atomistic simulations of the behaviour of nuclear fuel under irradiation can give access to its thermal properties and their evolution with temperature and irradiation. Knowledge of the thermal conductivity of 100% dense oxide can now be obtained by molecular dynamics and the interatomic force constants[1] at the single crystal scale, but the effect of defects induced by irradiation (irradiation loop, cluster of gaps) or even grain boundaries (ceramic before irradiation) remain difficult to evaluate in a coupled way.
The ambition is now to include defects in the supercells and to calculate their effect on the force constants. Depending on the size of the defects considered, we will use either the DFT or an empirical or numerical potential to perform the molecular dynamics. AlmaBTE allows the calculation of phonon scattering by point defects [2] and the calculation of phonon scattering by dislocations and their transmission at an interface have also recently been implemented. Thus, the chaining atomistic calculations/AlmaBTE will make it possible to determine the effect of the polycrystalline microstructure and irradiation defects on the thermal conductivity. At the end of this post-doc, the properties obtained will be used in the existing simulation tools in order to estimate the conductivity of a volume element (additional effect of the microstructure, in particular of the porous network, FFT method), data which will finally be integrated into the simulation of the behavior of the fuel element under irradiation.
The work will be carried out at the Nuclear Fuel Department of the CEA, in a scientific environment characterised by a high level of expertise in materials modelling, in close collaboration with other CEA teams in Grenoble and in the Paris region who are experts in atomistic calculations. The results will be promoted through scientific publications and participation in international congresses.
References:
[1] Bottin, F., Bieder, J., Bouchet, J. A-TDE
Thermodynamic investigation of Metal-Insulator-Transition materials – The case of doped VO2 for smart windows applications
The present post-doc proposal aims to develop a specific thermodynamic database on the V-O-TM (TM=Fe,Cr) system by using the CALPHAD approach. The candidate will conduct experimental campaigns to obtain relevant data to feed the thermodynamic models. The candidate will mostly use the experimental equipment available at the lab (DTA, annealing furnaces, high temperature mass spectrometry, laser heating, SEM-EDS). In addition, the post-doc may participate to combinatorial high-throughput activities led by other laboratory of the Hiway-2-Mat consortium (e.g., ICMCB in Bordeaux), allowing a better connection between the CALPHAD simulation output and the accelerated characterization platform. The thermodynamic database will be then included in the autonomous research routine implemented in the material exploration path.
Role of metal containers on the alteration of high-level waste confinement glasses in geological storage conditions: glass-iron interactions in hydrogen-tight reactors
Vitrified waste resulting from nuclear power plant fuel reprocessing, as well as their steel containers and overpacks, are intended for permanent storage in deep geological layers. Water will be the vector of glass alteration and potential migration of radioactive elements. The most advanced storage concept to date provides for the glass package to be protected for its thermal decay step from interaction with water by an unalloyed steel overpack. However, whether in the form of metallic iron or corrosion products of steels (oxides, carbonates, sulfides), iron plays a significant role in glass alteration.
The objective of this work is to understand and quantify the mechanisms of glass-iron interaction in order to strengthen the operational models for waste package performance. To this end, a bench of ten hydrogen-tight instrumented reactors has been developed in the laboratory. It has allowed the implementation of a first series of long-term experiments of several months, which concerned a non-radioactive model glass and a iron carbonate. The objective will be to carry out these interaction experiments using metallic iron this time, to characterize the sampled solutions and neoformed alteration products, and to interpret the experiments using the modeling tools available in the laboratory.