Numerical analysis for a molten salt reactor in the presence of localized perturbations

Molten salt reactors (MSRs) have seen a marked resurgence of interest over the past few decades, highlighted by their inclusion as one of the six Generation IV reactor types. The MSRs are characterized by using the fluid-fuel, so that their technologies are fundamentally different from those used in the conventional solid-fuel reactors. In this paper, the attention is focused on the behaviors of an MSR in the presence of localized perturbations caused by fissile precipitates and gas bubbles. A neutron kinetic model considering the fuel salt flow is established based on the neutron diffusion theory, which consists of two-group neutron diffusion equations for the fast and thermal neutron fluxes and six-group balance equations for delayed neutron precursors, and the group constants dependent on the temperature are calculated by the code DRAGON. In addition, the k-epsilon turbulent model is adopted to establish the flow and heat transfer. The thermo-hydraulic and neutronic models are coupled through the temperature, heat source and velocity. The effects of the localized perturbation on the distributions of power, temperature, neutron fluxes and delayed neutron precursors are obtained and discussed in detail. The results provide some valuable information for the research and design of this new generation reactor.

► The delayed neutron precursors move toward the outlet due to fuel salt flow.
► The power density and temperature increase sharply in the fissile lump region.
► The thermal neutron flux decreases in the fissile lump region.
► The thermal neutron flux increases in the gas bubble region.
►  MOSART has a great safety margin in the postulated extreme condition.