Molten Salt Reactors (MSRs) are presented as inherently stable systems with respect to reactivity perturbations, due to the strong coupling between salt temperature and nuclear power, leading to a homeostatic behavior of the reactor. However, although MSRs offer interesting safety characteristics, the limited operational experience available restricts our knowledge of their dynamic behavior.
This research work aims to contribute to the development of a methodology for analyzing the dynamics of MSRs, with the goal of characterizing complex neutron-thermohydraulic coupling phenomena in an MSR operating in natural convection, identifying potentially unstable transient sequences, prioritizing the physical phenomena that cause these instabilities, and proposing simple physical models of these phenomena.

This work will contribute to the development of a safety-oriented methodology that will help MSR designers better understand and model the reactor dynamic behavior during transients, through dimensional analysis and the study of the flow stability. This methodology aims to define simple and robust criteria to ensure the intrinsic safety of a fast-spectrum MSR, depending on its design and operational parameters allowing compliance with the operating domain limits.

This PhD lies at the crossroad of theoretical analysis of the physical phenomena governing the MSR’s behavior, particularly the study of unstable regimes (oscillatory or divergent in nature) due to neutron-thermohydraulic coupling under natural convection conditions, and the development of analytical and numerical tools for conducting calculations to characterize these phenomena.

The PhD student will be based within a research unit dedicated to innovative nuclear systems. He/she will develop skills in MSR modelling and safety analysis, and will have the opportunity to present his/her work to the international MSR research community.