Coupled neutronics and thermal-hydraulics calculation code development for molten salt reactor

A particular feature of the molten salt reactor (MSR) is that the liquid FLIBE salt is circulating through the primary loop simultaneously acting as both fuel and coolant. There is a significant difference in neutronics between MSR and conventional reactors using solid fuel. Thus, current modeling methods are not applicable for MSR. The flow circulation of MSR strengthens the coupling between neutronics and thermal-hydraulics (THs). It requires the study on the coupling among fluid flow, heat transfer and neutronics. In this paper, the Variational Nodal Method (VNM) is used to solve the neutron diffusion equation for its efficiency and stability. The improved quasi-static method is employed to treat the time-dependence to save computational time. For the delayed neutron precursors (DNP), the implicit difference method and fine mesh method are adopted for the reason of stability. In addition, based on the geometry feature of MSR, multiple channel THs model is employed. They are coupled by fuel and graphite temperature, heat source and fuel velocity. Numerical results show that the method developed by this paper is effective and accurate for MSR analysis and the fuel circulation has significant effect on the transient behavior of MSR.