Conditioning of waste from a NaCl-MgCl2 molten salt reactor
In recent years, interest in molten salt nuclear reactors (MSR) has been revived in France and abroad, and the use of chlorinated salts is now being considered. Irrespective of the technological issues to their development, the credibility of this approach depends on the controlled management of the final waste produced during the operation of such reactors. This involves a conditioning stage, which needs to be developed in line with the nature of the waste in question.
The conditioning of two types of waste, resulting from the treatment of spent fuel from a NaCl-MgCl2 molten salt reactor according to different scenarios, is the subject of this post-doctorate, which will be structured in two distinct directions.
The first part of the post-doctorate is dedicated to the vitrification of solutions with complex compositions and enriched in magnesium compared to the usual vitrified fluxes. For this purpose, an aluminoborosilicate matrix is being considered. In order to validate the feasibility of such vitrification, it is essential to assess the microstructure, structure and chemical durability of the resulting glasses, with regard to the expected magnesium contents. Thus, a series of aluminoborosilicate glasses with variable magnesium content will be developed and characterized. The study of these glasses alteration in aqueous solution will be coupled with their structural characterization (Raman, RMN).
The second line of the post-doctorate is dedicated to the conditioning of chlorinated waste, in particular alkaline and alkaline-earth chlorides. In this case, the conditioning method currently favored is ceramization, and will be the subject of a bibliographic study. The chosen route(s) will be tested and characterized, and its containment performance determined.
Skills required: materials science, glass, ceramics, taste for experimentation. Knowledge of Raman will be appreciated.
Development, metrological validation and outdoor testing of a multitrack Raman/FO measurement unit dedicated to the safety of future cryogenic liquid hydrogen dispensing stations
Context: The domestic and industrial use of liquid hydrogen as the fuel of the future requires the definition of a suitable safety code. At present, tank separation criteria have been defined by anticipation using a conservative approach. It is therefore necessary to carry out full-scale experiments ("pool spreading") in order to provide input for calculation codes and build relevant standards. These experiments require the implementation of instrumentation adapted to the measurement of all gases present in free space (O2, N2, H2O, H2) in order to establish a measurement of partial pressures during each test, correlated with the other means of measurement in place (thermometry, catharometry, PIV, BOS, etc.).
Mission: In the context of an ANR-PEPR project (ESKHYMO) managed by CEA Liten, a Raman/FO Multitrack spectrometric measurement unit will be developed jointly by CEA List and CEA DES on the basis of an existing device. Raman measurement is multi-elemental, multi-track (a single measurement unit for several probes), non-explosive, and delivers a self-standardized measurement to a reference species (usually nitrogen at atmospheric pressure). The Raman/FO measurement unit comprises a laser, a spectrometer associated with a scientific CCD camera, and a fiber-optic circuit for remote measurement. The design of the Raman/FO probes will also be based on an existing CEA product, which will be miniaturized for deployment in field conditions. Four Raman/FO probes will be produced and then calibrated in air (climatic chamber) and hydrogen (shock tube or vacuum chamber) at CEA DES DM2S in Saclay. Finally, the final device will be deployed on the test site for multi-gas measurements during spraying experiments, in partnership with Air Liquide and accrediting bodies (INERIS).
Skills: Optics, laser, fiber optics, spectrometry
Manufacturing of analytical microsystems by thermoplastics micro-milling
Micro-fabrication techniques and especially micro-milling can be used to manufacture microsystem prototypes with a timescale of days, as close as possible to the application. Polymethylmethacrylate (PMMA - Commercial name Plexiglas) is a commonly used material for microsystems fabrication, limited however by its chemical incompatibility with acids and solvents.
The goal of this post-doctoral project is to study the feasibility of machining thermoplastic materials other than PMMA and to optimise the associated manufacturing parameters. The post-doctoral project will start with the selection of materials in line with the aimed applications (optical and physico-chemical properties). The materials will be selected among the thermoplastics family (PC, POM, PS, HDPE, PEEK, PVC, PP, PTFE, ULTEM, etc).
The optimisation of the micro-milling step will be realized by varying parameters such as the tool rotation speed, the feed rates, the depth of cut, etc. The surfaces and channels will be characterized by optical or mechanical profilometry, optical microscopy and/or scanning electron microscopy.
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.
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
Seismic behavior of an overhead crane
Overhead cranes are part of the equipment in industrial installations to which special attention must be paid. They are generally located in the upper part of buildings and are potentially subject to significant levels of acceleration in the event of an earthquake, due to the amplification induced by the supporting structure. Consequently, they are potentially subjected to significant forces and can be the source of significant forces on the supporting structure. This study is a continuation of two previous test campaigns carried out on the Azalée shaking table of the EMSI laboratory, on a mock-up of an overhead crane. It aims to provide validated numerical models of this kind of equipment. Two lines of research are considered. The first axis aims to complement the “historical” test campaigns with static tests to justify the adjustment of the numerical models. The second axis consists of exploiting, by comparison tests/calculations, all of the tests that were carried out as part of a previous test campaign for statistical analysis purposes.
Design of new microfluidic tools for liquid-liquid extraction chemical processes
This 12-month post-doc proposal is part of the PIA MiRAGe: Future Investment Plan “Microfluidic Tools for Accelerated R&D on Recycling Processes”.
The MIRAGE project aims to provide a set of micro and millifluidic tools, platforms and methods to accelerate, intensify and make more flexible R&D on new recycling processes for strategic metals, nuclear or non-nuclear, while minimizing quantities of materials used.
To do this, new microfluidic tools have been designed at CEA ISEC to perform counter-current liquid-liquid extraction operations. These tools make it possible to redefine the orders of magnitude in the importance of the physico-chemical phenomena involved.
The interest of this invention is twofold and will be the core work of this post-doc:
- Carry out extraction operations over very low times and liquid volumes.
- Transpose this invention to larger volumes.
Thus, initially this post-doc work will seek to study in more detail the capabilities of this new microfluidic device, then to transpose this new technique to larger contactors.
The work will be carried out in the ISEC facilities at the CEA, on the Marcoule site in partnership with the CNRS, Universities and the INP of Toulouse.
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.
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