Dynamics and Stability Analysis Study of a Thermal Molten Salt Reactor

Molten salt reactors provide several advantages over conventional solid-fuel reactors regarding fuel options, waste minimization possibilities, and design flexibility. Furthermore, it requires a non-zero steady-state reactivity for reactor operation. This steady-state reactivity has to compensate for the loss of reactivity due to the loss in delayed neutron fraction because of the fuel salt circulation. These differences may pose challenges to the reactor dynamics behavior and its stability. Using the Monte Carlo code, Serpent, a thermal molten salt reactor, was modeled, and the fuel was depleted under constant power. The reactor kinetic parameters were evaluated at different stages during operation. These parameters were used as input for a dynamics simulator. The dynamics simulator was developed using the reactor kinetics and heat transfer models coupled through a temperature reactivity feedback model. The reactor response due to a reactivity insertion at different stages of the operation time was investigated. Results showed that the temperature reactivity coefficients become more negative as the fuel is burned. Thus, the stability of the molten salt reactor increases with the reactor operation time, similar to that of solid-fuel reactors. In addition, with the reactor operation time, the change in the fuel salt temperature exiting the reactor core during a transient event becomes more limited.