An approach to the MSR dynamics and stability analysis

•Study of the point kinetics of Molten Salt Reactors (MSR).•Comparison between the dynamic characteristics of fast- and thermal-spectrum MSRs.•Analysis of the stability margins of MSRs operating at different power levels.•Parametric analysis of the dynamic behaviour of MSRs as a function of the fuel velocity and the temperature feedback.

The first efforts in the development of the molten salt reactor technology were carried out in the sixties by the Oak Ridge National Laboratory and culminated with the design of the thermal-spectrum Molten Salt Breeder Reactor (MSBR). Only recently, the attention has been focused on fast-spectrum configurations, such as the Molten Salt Fast Reactor (MSFR) proposed in the framework of the Euratom EVOL (Evaluation and Viability of Liquid Fuel Fast Reactor System) Project, thanks to their favourable characteristics in terms of sustainability, waste minimization and improved safety. As a matter of fact, the MSFR has been recognized as a long term alternative to solid-fuelled fast neutron systems and has been identified as Gen-IV reference MSR configuration. From the dynamic behaviour point of view, the main feature that characterises this kind of systems is the presence of a liquid fuel that circulates in the primary circuit acting simultaneously as coolant. This feature leads to a complex and highly coupled behaviour, which requires a careful investigation, due to some peculiarities like the drift of delayed neutron precursors along the primary circuit. Although considerable studies have been carried out for the analysis of the graphite-moderated MSRs, the adoption of a fast spectrum configuration without graphite in the core is expected to notably modify the dynamic characteristics of the system, thus requiring further investigation. This work proposes an approach to the dynamics and stability analysis of molten salt reactors. In particular, the well-developed methods of the theory of linear systems are applied to the analysis of two case studies, namely: the MSBR and the recently proposed MSFR. This analysis is intended to provide a basic understanding of the inherent stability properties and of the dynamic characteristics of such kind of nuclear reactors, highlighting the main peculiarities of the new design compared with the more familiar graphite-moderated concept.