Flow Field Effect of Delayed Neutron Precursors in Liquid-Fueled Molten Salt Reactors

In molten salt reactors(MSRs), the liquid fuel salt circulates through the primary loop and a part of the delayed neutron precursors(DNPs) decays outside the reactor core. To model and analyze the flow field effect of DNPs in channel-type liquid-fueled MSRs, a three-dimensional space-time dynamics code, named ThorCORE3D, that couples neutronics, core thermalhydraulics, and a molten salt loop system was developed and validated with the Molten Salt Reactor Experiment(MSRE) benchmarks. The effects of external loop recirculation time, fuel flow rate, and core flow field distribution on the delayed neutron fraction loss of MSRE at steadystate were modeled and simulated using the ThorCORE3D code. Then, the flow field effect of the DNPs on the system responses of the MSRE in the reactivity insertion transient under different initial conditions was analyzed systematically for the channel-type liquid-fueled MSRs. The results indicate that the flow field condition has a significant effect on the steady-state delayed neutron fractions and will further affect the transient power and temperature responses of the reactor system. The analysis results for the effect of the DNP flow field can provide important references for the design optimization and safety analysis of liquid-fueled MSRs.