PhD position on analytical chemistry and electrochemistry - M/F

PhD position on analytical chemistry and electrochemistry - M/F

France 01 Nov 2022


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01 Nov 2022
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The Irène Joliot-Curie Physics Laboratory of 2 Infinities (IJCLab) is a physics laboratory under the supervision of the CNRS, the University of Paris-Saclay and the University of Paris. IJCLab was born in 2020 from the merger of five units (CSNSM, IMNC, IPN, LAL, LPT). The staff is made up of nearly 560 permanent (340 engineers, technicians and administrators and 220 researchers and teacher-researchers) and approximately 200 non-permanent including 120 doctoral students. The research themes of the laboratory are nuclear physics, high energy physics, theoretical physics, astroparticles, astrophysics and cosmology, particle accelerators, energy and the environment and health. IJCLab has very significant technical capacities (around 280 IT) in all the major fields required to design, develop or implement the experimental devices necessary for its scientific activity, as well as the design, development and use of instruments.
The Ph.D student will be enrolled in the Particles, Hadrons, Energy, Nuclei, Instrumentation, Imaging, Cosmos and Simulation (PHENIICS) doctoral school at Paris Saclay University. The scientific domains of PHENIICS include particle physics, nuclear physics, cosmology and astrophysics, nuclear energy, and theoretical physics particularly where there is a strong dialog with experiment (phenomenology, quantum field theory, gravitation, the N-body problem, etc). A vibrant instrumentation program covers accelerator and detector physics, including simulations and optimization. The applications and societal aspects of these domains, like radiochemistry and medical imaging, round out the PHENIICS offering and provide a multifaceted educational experience for the doctoral students of the University of Paris-Saclay. The field of the thesis project falls within the "Nuclear energy" axis since it concerns the treatment of the spent nuclear fuel.
This thesis project will be carried out in the CHIMèNE team of the Energy & Environment pole, in collaboration with ORANO. Sylvie Delpech's group has the skills and equipment necessary to develop studies in molten salt environments on elements such as thorium or uranium.

Molten salt reactors based on chloride salts are currently being studied for their particularity in having a fast neutron spectrum which makes them interesting for the transmutation of actinides. In the current French fuel cycle, uranium and plutonium are extracted from spent fuel by the PUREX process for later use (in MOX fuels or for future generation reactors). Minor actinides and fission products are conditioned by vitrification for their ultimate storage (planned for deep storage in the CIGEO storage site). Actinides contribute almost 95% of the waste radiotoxicity, while they represent only 0.2% of the total volume. The elimination of minor actinides from waste would significantly reduce their radiotoxicity and environmental impact. One of the preferred routes, pending the deployment of 4th generation reactors, is their transmutation by fission in a nuclear reactor. This must have certain characteristics such as (i) operate with a fast neutron spectrum and (ii) use regularly regenerated fuel in order to separate actinides / fission products, the fission products often being neutron poisons which capture neutrons and decrease the efficiency of transmutation. The chloride-based molten salt reactor is therefore a concept well suited to meet these objectives.
The objective of this thesis is to study the molten salt NaCl-ThCl4-CeCl3 (60-23-17 mol%) at 600 °C (cerium being used as a substitute for plutonium). The addition of thorium makes it possible to decrease the melting temperature and also to increase the safety of the reactor through the Doppler effect (neutron effect due to the presence of fertile material in the reactor). In addition, a controversy currently exists on the different stable oxidation states of thorium in molten chloride medium. On the basis of this preliminary knowledge, the first studies to be carried out within the framework of this thesis will relate to the chemical and electrochemical behavior of thorium in molten chloride medium and to the determination of the different stable oxidation state in this medium.
The second part of the thesis will concern the development of a pyrochemical treatment method for spent fuel. In a molten salt reactor, one of the reprocessing processes recommended to extract and separate the actinides (An) from the lanthanides (Ln) is the reductive extraction which consists in bringing the molten salt into contact with a sheet of bismuth (or other metal of interest) liquid and transfer the elements An and / or Ln by a redox reaction in the liquid metal. In the reductive extraction process, developed in the USA by the Oak Ridge National Laboratory in the 1960s, a reducing element is generally introduced into the liquid metal, typically lithium or sodium metal (corresponding to mixtures Bi-Li or Bi-Na). This metal is oxidized during the redox reaction and is transferred to the salt phase. The composition of the salt and of the liquid metal phase is then changed. The process is therefore not optimal in terms of material flows. Moreover, the experimental tests carried out recently have shown that the sheet of liquid metal quickly saturated with extracted elements, which limits the process.
The alternative proposed in this project is the dynamic reductive extraction (DRE) which consists in (i) carrying out the extraction by an electrolysis which makes it possible to avoid the presence of a reducing metal and thus to eliminate the problem of the evolution of the composition of the phases and (ii) to extract, in a second molten salt, from the sheet of liquid metal the elements which are reduced therein, simultaneously with their extraction, which eliminates the problem of the saturation of the liquid metal. During this thesis, electrochemical studies will be carried out in order to identify the reactions taking place at metal / salt interfaces. The extraction / separation kinetics of the ERD will be determined by ICP-AES (which makes it possible to analyze traces) by taking samples of salts and also by electrochemistry by following the disappearance (on one side) and the appearance (on the other side) electrochemical signals characteristic of the elements studied. The analytical relationship on the potential to be imposed will be established as a function of the redox properties of the elements and the experimental conditions and the anode and cathode materials will be optimized.

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