Description du sujet de thèse

e)Molten salt nuclear reactors (MSRs) have great potential in terms of safety and flexibility. These are reactors in which the fuel is dissolved in a mixture of molten salts (liquid), acting also as the coolant. The salt circulates in the fuel circuit through an area called the "core" where it is made critical by geometry, producing heat, which it extracted by passing through a heat exchanger, thus allowing the energy produced to be used, either in the form of heat (heat-generating role) or electricity (power-generating role). This type of reactor is characterized by its intrinsically core stable behavior, and its versatility (choice of cycle, choice of neutron spectrum, choice of salt composition, etc.) and therefore the versatility of its applications (power reactor on a range from very small to very large power, burner of high activity and long-life waste by transmutation, etc.). As these qualities are sought after in the current nuclear context, it is attracting renewed interest in France, in Europe and in the world.
For about twenty years, the CNRS, through the MSFR (Molten Salt Fast Reactor) team of LPSC (Laboratoire de Physique Subatomique et de Cosmologie), has been studying this type of reactor in various forms, and in particular the so-called reference MSFR, a high-power breeder reactor operating in the Thorium cycle and with a fluoride salt. The SEN (Structure and Nuclear Energy) team of SUBATECH (Laboratoire de Physique SUBAtomique et TECHnologies Associées) joined this theme a few years ago with a particular interest in the aspects of neutronics and associated calculations of residual power.
Taking into account the renewed interest for this promising technology, new collaborations have been set up, and new studies are in progress, in particular those around the MSR concepts of chloride salt actinide converter: among which the ARAMIS (Advanced Reactor for Actinides Management in Salt) reactor carried by the CEA and studied in the framework of the national ISAC (Innovative System for Actinides Conversion) project which began in the first half of 2022 and whose partners are: CEA, CNRS, EDF, FRAMATOME and ORANO. The ISAC project aims to study the capacity of a breakthrough technology, in this case the MSR, to reduce the inventory of actinides from the existing reactor fleet via the transmutation of minor actinides, by carrying out a sketch study (evaluation of design options, performances of the concept, operational and safety analysis) and by associating with it the first small-scale experiments on the main barriers of this technology: the chemistry of the salts, treatment/recycling, and the prevention of corrosion applied to the materials making up the primary circuit. Scenario studies will be associated in order to evaluate the final impact on the inventory and the type of waste to be stored according to different hypotheses.
The subject of the PhD thesis proposed here will be to contribute firstly to the definition of the outline in collaboration with the different partners of the consortium, via the neutronic studies of the ARAMIS reactor. The thesis will focus on the calculation of the core and cycle performances, on the sensitivities to nuclear data, as well as on the study of the residual power. Other studies may be undertaken by the PhD student, depending on the progress of the thesis and of the ISAC project, with a participation in risk analysis in collaboration with EDF and Framatome. The thesis, which will be supported by the two laboratories LPSC and SUBATECH, will be carried out 50% in Nantes at SUBATECH and 50% in Grenoble at LPSC.
The neutronic studies will be performed with the SERPENT evolution code for core characterization taking into account the on-line fuel processing scheme for the defined concept. Developments of the SERPENT code, specific to the MSR technology (constraints on the reactivity and/or the fuel composition during evolution) are currently underway at the SUBATECH laboratory. The results of these studies will also be compared to those obtained with the REM code developed in Grenoble since more than 20 years and which is currently the reference evolution code for the MSR concepts. Sensitivity studies to nuclear data will be performed with the Coconust and Cocodrilo codes developed at SUBATECH and LPSC. A work on the needs for improvement of nuclear data related to residual power will be carried out in the framework of the thesis. The PhD student may also use the coupled multiphysics codes developed at LPSC for the calculation of normal and accidental transients of MSR, in particular the coupled 3D code TFM-OpenFOAM and the system code LiCore. Finally, a part of the thesis work will involve a participation in the safety analysis of the reactor and more specifically on the risks associated with the use of americium as fuel.
In addition, the LPSC and SUBATECH laboratories are collaborating in the European projects SAMOSAFER (Simulation Models and Safety Assessment for Fluid-fuel Energy Reactors) and MIMOSA (MultI-recycling strategies of LWR SNF focusing on MOlten SAlt technology), and the PhD student will have the opportunity to present his/her work in these European frameworks and also to contribute to the working groups of these projects in relation to the PhD thesis subject.
The candidate must have a Master's degree in nuclear or reactor physics or equivalent. He or she must:
- Have a good knowledge of reactor physics (neutronics, thermal-hydraulics, safety...)
- Have a good knowledge of the use of an evolving neutronic code, dealing with the coupling of Boltzmann (neutron transport) and Bateman (material evolution) equations
- Be able to work in a team in the context of a wide range of collaborations
- Be used to developing computer code, especially in Python and Java
- Ability to produce large amounts of data
- Fluency in French and scientific English, both spoken and written
- Be rigorous: know how to report, respect deadlines.

Contexte de travail

The PhD student under CNRS contract will be based during the first half of the thesis at the SUBATECH laboratory in Nantes and during the second half at the LPSC laboratory in Grenoble. The research work will be multidisciplinary, ranging from reactor physics, nuclear data and safety analysis.
The Grenoble Laboratory of Subatomic Physics and Cosmology (LPSC) (http://lpsc.in2p3.fr) is a joint research unit associating CNRS-IN2P3, Grenoble Alpes University (UGA) and Grenoble INP school, for an average staff of about 230 people. The PhD student will be assigned́ to the MSFR Team composed of 2 LPSC staff (1 professor and 1 emeritus research director) and will be placed under the direct hierarchical authority of the team leader (E. Merle).
The laboratory of SUBAtomic Physics and Associated Technologies (http://www-subatech.in2p3.fr ) is a joint research unit located in Nantes and associating the CNRS-IN2P3, Nantes University and the IMT Atlantique school for an average staff of about 180 people. The PhD student will be assigned to the Structure and Nuclear Energy Team composed of 5 SUBATECH staff (3 professors, 2 CNRS researchers) and will be placed under the direct hierarchical authority of the head of the Reactor Simulations and Residual Power theme (L. Giot).