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.
Improvement of the AmSel process for americium recovery within TRANSPARANT European project
Uranium and plutonium can already be industrially separated from spent nuclear fuels by the PUREX solvent extraction process. By recovering americium from a PUREX raffinate, the capacity of a deep geological repository can be increased by a factor of up to seven. This separation became feasible by ingeniously combining the selectivity of a suitable extracting agent (TODGA) and a water-soluble complexing agent (PrOH-BPTD). The former co-extracts americium, curium, and lanthanides into the organic phase, rejecting other fission products (FP). The development of this process, called AmSel, was already initiated during previous European projects but the selectivity could be further improved, especially the Cm/Am separation factor. In order to separate those elements, which have very close physico-chemical properties, both the lipophilic extractant molecule in the organic phase and the complexing agent in nitric acid medium should be optimized. Batch extraction tests will be performed in glove boxes in ATALANTE facility at CEA Marcoule with radionuclides of interest (241Am, 244Cm, 152Eu). The behavior of relevant fission products (e. g. Tc, Pd, Zr, Mo, Ru, Sr) both in extraction and stripping conditions will also be evaluated. Experiments using a simulated feed solution containing all elements (including americium) in nominal concentrations will validate the loading capacity and separation performances. The resistance towards radiolysis of the selective ligand used as Am stripping agent in the aqueous phase will be evaluated by in situ alpha irradiations with 241Am in nominal concentration. Degradation will be evaluated by ESI-MS measurements coupled with HPLC to both identify and eventually quantify degradation products and complexes formed with those compounds.
Quasi-particle finite amplitude method applied to the charge exchange process in nuclear strength function models
Quasi-particle finite amplitude method (QFAM) has become the tool of choice to perform fast and accurate calculations of the nuclear strength function. Such a method is particularly interesting when applied to deformed nuclei, where traditional approaches based on large-scale matrix diagonalizations becomes almost intractable.
The goal of the current project is to extend the QFAM code developed at CEA to allow for charge exchange process and to calculate rates of ß- decay for all medium-mass and heavy even-even nuclei between the valley of stability and the neutron drip line using the newly fitted Gogny interactions.
By creating a shared databases of ß- decay rates with collaborators working in other CEA research units, we will perform systematic comparison with existing data in order to identify possible outliers and/or discrepancies.
Development of new Potassium-ion cells with high performances and low environmental impact
Lithium ion batteries are considered as the reference system in terms of energy density and cycle life and will play a key role in the energetic transition, especially concerning electric vehicles. However, such a technology involves the use of a large amount of critical elements and active materials are synthesised using energy intensive processes.
In this way, our team is developing a new Potassium-ion batteries technology with high performances but with a low environmental impact.
For this innovative and ambitious project, CEA-LITEN (one of the most important research institute in Europe) is looking for a talented post-doctoral researcher in material chemistry. The post-doctoral position is opened for a young researcher with a high scientific level, interested by valorising her/his results through different patents and/or scientific publications.
MULTI-CRITERIA ANALYZES OF HYDROGEN PRODUCTION TECHNOLOGIES BY ELECTROLYSIS
LITEN, strongly involved in electrolysis technologies, wishes to compare via a multi-criteria analysis all electrolysis technologies currently available commercially (AEL, PEMEL), in the pre-industrialization phase (SOEL), or in R&D (AEMEL and PCCEL).
Our previous studies were based on specific use cases (fixed hypotheses on the size of the factory, the source of electricity, the technology, etc.).
The objective of this new work is to be able to position the different electrolysis technologies according to parameters which will be defined at the start of the project, these parameters being of a contextual type (e.g. number of operating hours, expected flexibility), technical ( ex yield, lifespan) or technical-economic (ex CAPEX OPEX) and environmental (ex GHG impacts, materials). The aim here will be to develop an original methodology which makes it possible to define the areas of relevance of each of the electrolysis technologies according to these parameters, depending for example on the cost of the hydrogen produced and its environmental impact
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.
Study of the seismic behavior of piping systems using mechanical models of different degrees of fidelity
Piping systems are part of the equipment to which particular attention is paid as part of the safety review or design of nuclear installations. They are designed in accordance with codes, standards and regulations to withstand loads that occur or may occur over the life of a facility. These systems must therefore be designed to withstand accidental loads such as earthquakes. Feedback shows that piping systems generally behave well in the event of an earthquake. When failures are observed, they are more likely to be due to significant anchor movement, brittle materials, unwelded joints, corrosion, piping support failures, or seismic interactions. In practice, to be able to estimate the beyond design seismic behavior and the associated failure risks, the engineer can implement numerical models involving varying degrees of refinement depending on needs. This study consists of taking stock of the numerical modeling capabilities of piping systems under earthquake. For reasons of computational burden, global modeling based on beam elements is often favored, considering simplified material laws such as bilinear material laws with kinematic hardening. We know the “theoretical” limits of these models but it is difficult to have clear ideas about their real limits of applicability depending on the level of loading and the damage targeted. To make this assessment, we propose to interpret, using different numerical models involving different degrees of fidelity, the results of the experimental campaign carried out by the BARC and which was used for the MECOS benchmark (METallic COmponent margins under high Seismic loads).
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.).
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
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.