A multiphysics model for analysis of inert gas bubbles in Molten Salt Fast Reactor

Molten salt reactors (MSRs) have gained worldwide interest in recent years due to their appealing safety and resource utilisation characteristics. These reactors have a unique feature, i.e. the presence of nuclear fuel in the form of a molten fluoride or chloride salt containing the fissile and fertile materials. The fuel salt also acts as the coolant, and this dual role results in a complex, highly coupled multiphysics system which poses a challenge in modelling and simulation of MSRs. This paper presents the development of a simulation model for the Molten Salt Fast Reactor (MSFR) to predict the behaviour of inert gas bubbles in the core and to quantify their impact on the reactivity. Inert gas bubbles in MSFR have been modelled using a multiphysics approach coupling computational fluid dynamics for fluid flow and heat transfer with neutron diffusion equation for neutronics and a balance equation with diffusion and advection terms for taking into account the drift of the delayed neutron precursors. The two-phase flow has been modelled using a simplified Euler–Euler model for small volume fraction of the dispersed phase, i.e. for small bubble fraction, which combines the momentum and continuity equation of the liquid and gas phases and adds a gas-phase transport equation to track the void fraction. Simulations reveal that the bubble distribution in the core has a significant impact on reactivity resulting in a difference in the bubbling feedback coefficient compared to studies using a homogeneous distribution