Missions

The candidate will work as part of the EURAD2 European project coordinated by Andra on nuclear waste management. The aim of the study carried out at IJCLab is to develop an innovative method for managing metallic nuclear waste in the form of scrap and powder. The dismantling of the former Uranium Natural Graphite Gas (UNGG) nuclear reactors generated a large volume of metallic nuclear waste. Once the uranium metal fuel had been mechanically removed, the fuel cladding was cut up and placed in silos at La Hague and CEA Marcoule to await disposal. During this storage, debris and powders were formed at the bottom of these silos. For massive waste, it is proposed to incorporate it in a cement matrix adapted to the chemistry of metals, in a steel drum. However, this management method cannot be applied to small-sized waste. Because of their large specific surface area, such waste is more reactive than massive parts. The debris and powders are likely to react significantly by redox reaction with the water contained in the porous network of the cementitious matrices, thus forming hydrogen gas and corrosion products. Under these conditions, the integrity of the radioactive waste storage package can no longer be guaranteed because the conditioning matrix risks cracking. For waste in the form of debris and powders, we therefore propose an oxidising pre-treatment before incorporation into a conditioning matrix. This oxidation would be carried out in a molten salt environment, in the presence of water. The aim is to determine the oxidation mechanisms and kinetics of various metallic nuclear wastes in molten salts in order to define the optimum conditions for this process. This study will be carried out using a dual approach, thermodynamic calculations and an experimental approach using electrochemistry, gas chromatography, ICP-AES and XRD.

Activités

The work will focus on the reactivity of magnesium, zirconium, tungsten, uranium and graphite in various molten salts (hydroxide salts and hydrogen sulphates). The post-doc will contribute in particular to the following points:
• Calculate the thermodynamic potential-acidity diagrams of molten salts and of the metals in these salts.
• Determine the oxidation mechanisms of metals in molten salts: define the oxidant and the chemical form of the oxidised metal.
• Determine the oxidation kinetics of metallic waste by monitoring the oxidation reaction using gravimetry and gas chromatography (in the case of oxidation by water).
• Study the influence of the surface on the reactivity of the metal.
• Writing EURAD2 project deliverables and presenting the results at European meetings.
• Publish the results in scientific journals and present them at national and international conferences

Compétences

The candidate must hold a research doctorate in analytical chemistry. The position requires a knowledge of aqueous or non-aqueous solution chemistry, electrochemistry, a solid background in experimental chemistry and thermodynamic calculations. It would be interesting if the candidate had some knowledge of molten salt chemistry. Molten salts are complex media that require special experimental set-ups.
The candidate will also need good oral and written communication skills (in French AND English) to present his/her results at meetings and international congresses, and to write reports and articles in scientific journals. We are looking for a serious young researcher who can quickly become autonomous and get involved in the project, with a strong motivation to develop skills in the field of molten salt chemistry and the management of metallic nuclear waste. In addition, the candidate should be able to work as part of a team using the various techniques available to complete the project.

Contexte de travail

IJCLab is a physics laboratory under the supervision of the CNRS, the University of Paris-Saclay and the University of Paris, created in 2020 from the merger of five UMRs located on the university campus of Orsay. The research themes of the laboratory are nuclear physics, high energy physics, astroparticles and cosmology, theoretical physics, particle accelerators and detectors as well as technical research and development and associated applications for energy, health and the environment. The structure has very significant technical capacities (approximately 280 engineers and technicians) in all the major fields required to design, develop and implement the experimental devices necessary for its scientific activity: mechanics, electronics, IT, instrumentation, acceleration, biology techniques, radiochemistry and physics and chemistry for nuclear energy. These technical strengths represent a major asset for the design, development and use of the necessary instruments (accelerators and detectors). The presence of research infrastructures and technological platforms gathered on the laboratory site is also a major asset.
This contract will be carried out as part of the EURAD2 project in the Energy and Environment cluster - CHIMèNE team - CHANCE group of IJCLab. This research group is made up of four permanent staff, Sylvie Delpech (DR), Céline Cannes (CR), Davide Rodrigues (IR) and Tracy Bellande (T), and has suitable experimental platforms that have enabled the development of numerous projects in the field of molten salt chemistry and nuclear waste management. Examples include studies into the chemistry and reprocessing of molten salts (fluorides and chlorides) in the context of fast-spectrum molten salt reactors, the pyrochemical treatment of solid fuel, the chemistry of molten nitrate-based heat transfer salts for fast sodium reactors or concentrating solar power plants, the nitriding of low-carbon steels in molten carbonate media or the dissolution of powdery metallic waste in molten hydroxides. This solid experience in molten salt chemistry has been acquired through numerous studies in collaboration with the CEA, Andra and Orano, and through several European projects.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.