Comparison of Analytical Models for Frequency Response and Linear Stability of Molten Salt Reactors

This paper presents an exploratory study of the frequency response and linear stability of molten salt reactors (MSRs) using the continuous stirred-tank reactor (CSTR) and the plug flow reactor (PFR) models. Linear stability analysis is crucial to understanding the dynamic behavior of nuclear reactors, especially MSRs, which employ circulating liquid salt as both fuel and coolant. Unlike conventional reactors, the dynamic behavior of MSRs is influenced by the tight coupling between flow dynamics and neutronics, as well as the strong interzonal interactions within the core. This paper contrasts the two models, emphasizing the PFR’s ability to capture recirculation resonances and other kinetic phenomena neglected by the CSTR approximation. The developed theoretical models are applied to the Molten Salt Reactor Experiment (MSRE), and their predictions are compared with experimental data. This study also explores the sensitivity of reactor frequency response and stability to amplitude changes in fuel and moderator reactivity feedback mechanisms and the fuel flow rate. The findings demonstrate that both models provide an analytically solvable framework for MSR stability analysis. Despite the more involved theoretical basis of the PFR model, the CSTR model results are shown to correspond more closely to the reference MSRE data.