Research on the Neutron Kinetics for a Molten Salt Reactor during the Rod Drop Transient

摘要

The neutron kinetics of the molten salt reactor is significantly influenced by the fuel salt flow, which leads to the analysis methods for the conventional reactors using solid fuels is not applicable for the molten salt reactor. In this study, the 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. The mathematical equations are discretized and calculated by developing a numerical code, in which the implicit scheme is adopted for the time-dependent terms, and the power law scheme is for the convection-diffusion terms. The neutron kinetics is conducted during the rod drop transient, and the relative power change and the distributions of the neutron fluxes and delayed neutron precursors are obtained. The results show that, the core power reduces to less than 2% of its original value in 0.02s after the transient condition happens, and the ultimate power under the flow condition is lower than that without flow. Comparing the distributions of the fast, thermal neutron fluxes and the delayed neutron precursors in the core during rod drop transient with those under steady condition, it can be found that the fast and thermal neutron fluxes sharply decrease in the rod inserting region, while decrease a little in the other region. In addition, the results indicate that the delayed neutron precursors change a little during the rod drop transient, and the larger the decay constant, the greater the changes of the delayed neutron precursors. The obtained results serve some valuable information for the research and design of this new generation reactor.