New Sustainable Carbon Catalysts for PEMFC

The aim of the project is to develop and test for ORR, a mesoporous and graphitised graphene aerogel based material, presenting a hierarchical structuring allowing a better material transfer and graphitic domains increasing the durability and conductivity of the final material, and functionalised by Pt-NPs.
These graphene-based structures developed at IRIG/SyMMES possess surface chemistries and micro/meso/macro porosities that depend on the synthesis, functionalisation and drying methods used. The aim will be to increase their degree of graphitisation, and then to deposit Pt-NPs by chemical means. The electrocatalytic properties of these materials will then be tested.
Advanced meso-structural characterisation of these materials by scattering (X-ray or neutrons) methods will enable to investigate the structural properties of these new electro-catalysts. These properties will thenbe correlated to their electrocatalytic properties, and performances in fuel cell systems. This knowledge will be gained through ex-situ and operando analyses.

HPC simulation of electrode mechanical properties in Li-ion batteries

Li-ion batteries are complex multi-physics systems in which chemical reactions, transport phenomena, and mechanical deformation are strongly coupled. The battery electrodes are composed of micrometric granular materials (the microstructure) where the lithium can insert and disinsert, a process that creates internal mechanical stress and strain in the materials and subsequent volumic changes. While it is currently observed that the coupling between electrochemical reactions and mechanical deformation at the microstructure level strongly impacts the battery performances, lifespan and safety, the origin of this impact is poorly understood. The global objective of this position is to better understand the coupling between mechanical deformations of the microstructure and the local conditions of lithium transport in the electrode. The study should lead to practical applications such as recommendation on the electrode design to increase life capability of Li-ion batteries.

Study of the decontaminating melting of end-of-life nuclear fuel claddings

Currently, in France, UOx fuel cladding is made of zirconium and tin or niobium based alloys. At the end of the use of nuclear fuels in the reactor, the fuel claddings contaminated with actinides (An), fission products (FP) and activation products (AP) are stored awaiting their storage in a geological site.

It is planned to decontaminate these claddings, once the spent fuel has been removed, to make them less radioactive, with the aim of decategorizing them.
Studies on radioactive sheaths have shown that the use of a fluoride-based slag allows decontamination of An and FP towards the slag. The scientific obstacle lies in the decontamination in AP, and more precisely in the preliminary stage of Zr/Nb separation.
In addition, the management of fluoride slags should be avoided due to the strong tendency of fluorine to corrosion. The use of oxide slags would be an alternative way to be privileged, constituting the second challenge of this research project.

The objectives of the post-doctorate will initially be to formulate slags. Then, Zr alloy decontamination, Zr/Nb separation and separation of activation products will be studied.

The experiments developed, in a non-radioactive laboratory, will be based on a literature review carried out by the post-doc and on the results of thermodynamic calculations performed at the LM2T of CEA Saclay.
The missions of the post-doc will be to develop slags according to the operating conditions that he/she will have defined (composition, temperature), to characterize them using physico-chemical analyzes (SEM/EDS, XRD, TDA/TGA) and to test them, in the presence of duct sections, for decontaminating melting. The post-mortem analysis will allow to assess their decontamination capacity and to optimize, if necessary, the interactions at the interfaces and/or their chemical composition.

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.

Behavior of materials in molten salts

Access to clean and affordable Energy is a key challenge in the current context of climate emergency. Several leads have been considered for several years but technological issues remain up to date to make it happen. From concentrated solar plant to 4th generation of nuclear reactor, molten salt is a promising media (both for heat transfer fluid and the fuel itself). Nevertheless, due to the presence of impurities, molten salts are highly corrosive for commonly used materials.
Most of the commercial alloys - either nickel based or iron base - seems to suffer from rapid attack. It is then needed to broaden the scope of the studies by investigating innovative materials. Thus, a screening of materials is planned to select the most interesting ones. After a thorough filtering, a study of the corrosion mechanism will be carried out through analysis at different scales (SEM, DRX, SDL, ICP, etc … )as well via electrochemical techniques and thermodynamic modelisation (HSC and FactSage).
The aim of the post doctoral subject offered at the S2CM (Service of corrosion and Behavior of Materials) consists in the entire study of the behavior, from the sample preparation to the caracterization of corrosion products. This topic is highly experimental and goes deep in the understanding of the corrosion mechanisms. This post doc position is part of a project gathering top - Notch industrial and academics (EDF,Framatome, Orano and the CNRS). Results obtained are subject to be presented to the different partners.

Design of a crystal growth process

Laser fusion facilities, like LMJ, require the use of large optical components. Some of them are large KDP or DKDP (KDP partially deuterated) plates extracted from single crystals.
Currently, DKDP single crystals are produced a by slow growth method were the growth time exceeds two years.
Here, we proposed to study a rapid growth method to reducing the growth time to a few months.

Improvement by thermodynamic calculations of the modeling for the joint oxyde-gaine and the fuel cladding chemical interaction into the fuel performance code GERMINAL

This work is proposed in the frame of studies on the physico-chemical behaviour of the (U,Pu)O2 fuel during irradiation considered for the future reactors of 4th generation. Indeed, this kind of fuel is subject in particular to two specific specific phenomena that can have an impact on its behaviour:
- the formation of a JOG (Joint Oxyde-Gaine), a fission products layer localised between the external surface of the fuel pellet and the inner surface of the cladding material ;
- the FCCI (Fuel-Cladding Chemical Interaction), which leads to the formation of a corrosion layer on the internal surface of the clad containing fission products and elements constituting the cladding material.
The goal is this work is to improve the modelling of the JOG and of the FCCI into the fuel performance code (FPC) GERMINAL, dedicated dedicated to the calculation of the thermo-mechanical and physico-chemical behaviour of fast reactor fuel irradiated in normal and off-normal conditions. For that purpose, the candidate will work on the dedicated calculation scheme of GERMINAL which uses the thermochemical software OpenCalphad and on the comparison of the JOG and of the internal cladding corrosion widths obtained to experimental observations obtained for some irradiation experiments. Complementary stand-alone thermodynamic calculations will be performed with the TAFID, thermodynamic database on nuclear materials developed in an international framework, in order to analyse the thermochemistry JOG/FCCI versus parameters of interest.
This work will be performed in collaboration with a team specialised in thermodynamic modelling, in charge of the TAFID project. The student will thus have the opportunity to exchange on his results in a collaborative frame with international partners. In addition, he will be able to highlight his work through publications and presentations at conferences.

Implementation of a sensor allowing the online monitoring of the corrosion of stainless steels in a hot and concentrated nitric acid medium

The control of materials (mainly stainless steel) aging of the spent nuclear fuel reprocessing plant is the subject of permanent attention. Some installations at La Hague plant will have to be replaced very soon. In this context, it is important for the industry to develop sensors that are resistant to concentrated nitric acid (˜ 2.5 mol / L) and temperature (from ambient to 130 °C), allowing the online monitoring of the corrosion.
The aim of this work is to manufacture one sensor for the detection of corrosion of the steel intended for handling by the operators of the plant. In case of a positive response, the second sensor is used.
The challenges of this work are essentially technological since it will develop or use materials adapted to concentrated and hot nitric acid media.
The laboratory is specialized in the corrosion study in extreme conditions. It is composed of a very dynamic and motivated scientific team.

Optical sensor development for in-situ and operando Li-ion battery monitoring

To improve the battery management system, it is required to have a better knowledge of the physical and chemical phenomena inside the cells. The next generation of cells will integrate sensors for deepest monitoring of the cell to improve the performances, safety, reliability and lifetime of the battery packs. The main challenge is thus to measure relevant physico-chemical parameters in the heart of the cell to get a direct access to the real state of the cell and thus to optimize its management. To address this challenge, a research project will start at CEA at the beginning of 2020 to develop innovative optical sensors for Li-ion battery monitoring. He / She will participate, in a first step, to the development of optical probes and their integration on optical fibres. The work will focus on the synthesis of a photo-chemical probe (nanoparticle and/or molecule) as active part of the sensor. Then, theses probes will be put on the optical fibre surface to form the sensor. The candidate will also participate to the realization of an optical bench dedicated to the testing of the sensors. In a second step, he / she will work on integrating the sensors into the Li-ion cells and test them in different conditions. The objective is to demonstrate the proof of concept: validation of the sensors efficiency to capture the behaviour of the cell and correlate it to electrochemical measurements.

Nanostructured negative electrodes for magnesium-ion batteries

The subject is part of an ANR project on the development of negative electrodes for magnesium (Mg)-ion batteries. Magnesium is an excellent alternative to lithium due to its high specific capacity, low cost, abundance on Earth and low reactivity. However, conventional electrolytes interact strongly with metallic magnesium to form a blocking layer on the surface of metallic Mg, inhibiting reversible electrochemical reactions. An interesting solution to overcome this problem is to replace the Mg metal electrode with a material compatible with electrolyte solutions having a large electrochemical stability window. Interestingly, Mg alloy compounds have adequate stability in conventional electrolytes, slightly higher potentials than pure metallic Mg with however lower specific capacities than Mg. As part of an ANR project, the LEEL laboratory develops new alloy compounds for Mg batteries in the form of nanostructured electrodes to overcome volume expansion and slow diffusion of ions during the alloying with Mg.
In this project, the postdoctoral associate will first be in charge of the fundamental understanding of the reactivity towards the electrolyte of the alloys developed in the laboratory, notably through impedance spectroscopy and XPS. Secondly, the postdoctoral associate will deal with the electrode and electrolyte formulation’s optimization with a systematic comparison of electrochemical performances in half-cell. Finally, full Mg-ion cells will be made with the better electrode/electrolyte combination.