Conception et optimisation d’un réacteur de type MSFR en sels chlorures et en cycle uranium

This PhD thesis deals with the design and optimisation of a fast neutron spectrum molten salt Cl-MSFR reactor using the uranium cycle and chloride salts, with the aim of closing the fuel cycle and reusing the spent fuels produced by the current fleet of pressurised water reactors.The initial studies focus on the design and optimisation of the reactor in its initial configuration, taking as a starting point the reference MSFR using fluoride salts and the thorium cycle.Using the Serpent2 code for static neutronics calculations and the SONGe code for constrained optimisation of heat extraction, we first look at the circuit containing the fuel salt. This includes the reactor core, the recirculation loops incorporating the heat exchangers, and the expansion vessel. The sectors containing the fertile salt that enhances breeding, and the neutron shields that protect the heat exchangers, are then sized as best as possible from a neutronics point of view. This gives a basic configuration for the Cl-MSFR, on which the feedback coefficients, important for the intrinsic stability of the reactor, are assessed.The material composition evolution of the reactor over the course of its operation is then analysed, using the REM code, which performs depletion calculations driven by precision and allows continuous material feed and extraction to be taken into account. Following the definition of a treatment scheme suitable for chloride salts, these studies enable the fuel and fertile salt treatment rates to be optimised, the consumption of minor actinides to be estimated and the residual power of the system to be assessed, in comparison with the reference MSFR.Then, using the LiCore system code, the behaviour of the reactor is studied for a number of transients: reactivity insertion, load following, loss of flow at the pumps.The study of this reactor concludes with an analysis of its impact on deployment scenarios in France and worldwide, again in comparison with the reference MSFR.The final work concerns the preliminary analysis of another chloride-salt MSFR with a uranium-cycle burner core and a thorium-cycle fertile blanket, a tool for a fuel manager enabling the processing of current spent fuel and the production of new fuel (233U) for the reference MSFRs.