Optimization of an optical pyrometry measurement in a nuclear environment.
This topic focuses on the optimization of a contactless temperature measurement technique based on multispectral optical pyrometry for nuclear environments. The scientific objective is to improve the reliability of an instrumentation chain capable of measuring the temperature of a fuel cladding under extreme conditions, particularly during a loss-of-coolant accident. The method relies on collecting the infrared radiation emitted by the investigated surface and transporting it through optical fibers to a multispectral detection system. A key challenge is the simultaneous estimation of temperature and emissivity, two parameters that are strongly coupled in pyrometry. The work also aims to improve optical calibration, channel-by-channel transmission stability, and signal acquisition speed. Particular attention is given to the design of micro-sensors and optical collection heads compatible with pressurized, irradiating, and thermally constrained environments. The project includes the study of lower temperature measurement limits in order to extend the sensor’s operating range. Tests in a pressurized chamber will be carried out to validate sealing, optical transmission, and metrological robustness. From a scientific perspective, this postdoctoral project combines optics, radiometry, signal processing, metrology, and instrumentation for harsh environments. Ultimately, this technology could be transferred to other nuclear experiments requiring fast, accurate, and non-intrusive temperature measurements.
Improvement of High-Temperature Electrolyzer Interconnect Performance
High-Temperature Electrolyzers (HTEs) are currently being developed at the CEA for the production of “green” hydrogen. One of the components, the stainless-steel interconnect, is affected by two phenomena that progressively reduce cell efficiency: surface oxidation and chromium oxide volatilization. For these reasons, protective coatings are being developed at the CEA and with industrial partners. The performance of these samples (oxidation behavior, electrical resistance, etc.) must be evaluated both in contact with air, in contact with an H2/H2O mixture, and under dual-atmosphere conditions with the two environments on either side of the sample.
The proposed postdoctoral position includes several missions presented below:
• Development of an experimental setup to evaluate the oxidation behavior and area-specific resistance of coated and uncoated samples under all environmental conditions.
• Investigation of the observed phenomena using the many characterization techniques available at the CEA (SEM, Raman microscopy, TEM, GD-OES, XPS, XRD, etc.).
• Proposal of the degradation mechanisms involved and identification of the most relevant coating for industrial applications.
Development of advanced nuclear instrumentation for dose and contamination measurement on decommissioning sites.
This postdoctoral project focuses on the development of advanced nuclear instrumentation for dose and contamination measurement on decommissioning sites.
The approach is based in particular on online radiophotoluminescence measurement, in order to obtain sensitive radiological information that can be used in real time and adapted to constrained environments.
A major scientific challenge is to understand the physical mechanisms governing this measurement, from the creation of radiation-induced defects to their optical readout.
Silver-related defects play a central role, particularly their lifetime, temporal stability, and influence on signal reproducibility.
Controlling the excitation and emission processes, especially in the infrared range, is essential to improve sensitivity and the signal-to-noise ratio.
The project will aim to identify the limitations associated with weak signals, noise, drifts, component ageing, and disturbances specific to nuclear environments.
It will combine defect physics, optoelectronic instrumentation, acquisition electronics, ionising radiation metrology, and digital signal processing.
Filtering, drift correction, synchronisation, and anomaly detection methods will be developed to make online measurement more reliable.
System miniaturisation and integration will also be investigated to enable measurements as close as possible to the areas of interest.
The expected results will contribute to the experimental validation of the device and to the scientific dissemination of the project through publications, conferences, and supervision activities.
Development of isotopic and elemental analysis methods on irradiated fuels for the reduction of sample quantities.
The objective of this postdoctoral research is to develop analytical methods for the overall reduction of sample quantities required for high-precision multi-element isotopic analysis (actinides and PF) of spent nuclear fuel, particularly through the use of novel "low-quantity" introduction methods on multi-collector ICPMS. These developments will notably reduce the amount of radioactive waste (consumables and effluents), the dose rate, and the exposure time of analysts/radioactive samples associated with this type of measurements.
To carry out this project, the candidate will conduct analytical developments in a controlled environment to minimize the quantities of elements required for analysis while maintaining or improving uncertainty levels compared to currently available methods.
Impact of Microstructure in Uranium Dioxide on Ballistic and Electronic Damage
During reactor irradiation, nuclear fuel pellets undergo microstructural changes. Beyond 40 GWd/tU, a High Burnup Structure (HBS) appears at the pellet periphery, where initial grains (~10 µm) fragment into sub-grains (~0.2 µm). In the pellet center, under high temperatures, weakly misoriented sub-grains also form. These changes result from energy loss by fission products, leading to defects such as dislocations and cavities. To study grain size effects on irradiation damage, nanostructured UO2 samples will be synthesized at JRC-K, using flash sintering for high-density pellets. Ion irradiation experiments will follow at JANNuS-Saclay and GSI, with structural characterizations via Raman spectroscopy, TEM, SEM-EBSD, and XRD. The postdoc project will take place at JRC-K, CEA Saclay, and CEA Cadarache under expert supervision.
Thermochemical and thermodynamic study of chloride molten salts
In today’s climate emergency, access to clean and cheap energy is more important than ever. Several ways have been envisaged for several years now, but a number of technological issues still need to be overcome before they can be put into practice, as they represent breakthroughts. Whether for energy storage than for fourth generation nuclear reactors, molten salt environment used as coolant and/or as fuel is highly corrosive requiring a complexe choice of structural materials.
The aim of this subject proposed in the Corrosion and Materials Behavior Section is to study in depth the chemical properties of different chloride molten salts : the basic ternary salt (NaCl-MgCl2-CeCl3) but also the corrosion/fission/activation products that can be produced (MxCly with M=Cr, Fe, Te, Nd, Ni, Mo,…). The activity coefficients and solubility limits of these metallic elements will be determined using various techniques such as electrochemistry and Knudsen cell mass spectrometry. If required, this study can be completed by the phase transition temperature and heat capacity measurements using differential scanning calorimetry.
Optimizing phytotechnologies for the remediation of contaminated nuclear sites
CEA is recruiting a postdoctoral researcher for a research project aimed at optimizing phytotechnologies for the remediation of contaminated nuclear sites. This research is part of the risk management and remediation of contaminated soils, in particular those resulting from the decommissioning of nuclear facilities. The aim of the project is to develop an advanced mechanistic model of soil-plant transfers, in order to gain a better understanding of contaminant mobility in lightly contaminated soils, and to optimize the use of suitable plants to stabilize these contaminants.
Modeling the corrosion behavior of stainless steels in a nitric acid media with temperature
Controlling the aging of equipment materials (mainly stainless steel) of the spent nuclear fuel reprocessing plant is the subject of constant attention. This control requires a better understanding of the corrosion phenomena of steels by nitric acid (oxidizing agent used during the recycling stages), and ultimately through their modeling.
The materials of interest are Cr-Ni austenitic stainless steels, with very low carbon content. A recent study on Si-rich stainless steel, which was developed with the aim of improving the corrosion resistance of these steels with respect to highly oxidizing environments [1 , 2 ]; showed that the corrosion of this steel was thermally activated between 40 °C and 142 °C with different behavior below and above the boiling temperature (107 °C) of the solution [3]. Indeed, between 40°C and 107°C, the activation energy is 77 kJ/mol and above boiling point, it is much lower and is worth 20 kJ/mol. This difference may be due to a lower energy barrier or a different kinetically limited step.
The challenge of this post-doctoral subject is to have a predictive corrosion model depending on the temperature (below and beyond boiling). With this objective, it will be important to analyze and identify the species involved in the corrosion process (liquid and gas phase) as a function of temperature but also to characterize the boiling regimes. This model will be able to explain the difference in activation energies of this Si-rich steel below and above the boiling temperature of a concentrated nitric acid solution but will also make it possible to optimize the processes of the factory where temperature and/or heat transfer play an important role.
Design and accelerated testing of corrosion FOSs for reinforced concrete structures
Corrosion of steel reinforcement is the main pathology threatening the durability of civil engineering structures. Today, structures are mainly monitored by means of periodic visual inspections or even auscultation (corrosion potentials, ultrasonic measurements, core sampling, etc…), which are not very satisfactory. There is therefore a need for instrumentation capable of detecting the initiation and location of corrosion of reinforcement in concrete and ensuring long-term monitoring (several decades or more). In the context of Civil Engineering (CE) structures, Optical Frequency-Domain Reflectometry (OFDR) appears to be a suitable metrological solution because of its centimetre resolution and measurement range (70 metres in the standard version, i.e. several thousand measurement points along an optical fibre).
Content of work: The aim will be to adapt the design of this fibre optic sensor (FOS) to increase its durability and then to verify its applicability in the laboratory. Initially, the person recruited on a fixed-term research contract will be asked to work on the durability of the connexion between the optical fibre and the armature. Two different methods are envisaged: plasma torch spraying of ceramic powders and sol-gel. Both of these processes prevent the galvanic coupling because they involve insulating materials (ceramics) and are already deployed in industry in various civil and military fields. Secondly, test specimens equipped with the FOS will be tested in the laboratory according to classic civil engineering situations, i.e. localised corrosion (pitting induced by exposure to chloride ions) and uniform corrosion (generalised corrosion induced by carbonation of the embedding concrete). OFDR acquisitions will be carried out periodically over time in parallel with conventional metrology (potential, etc.).
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.