Development and verification of a three-dimensional spatial dynamics code for molten salt reactors

Abstract

Molten Salt Reactor (MSR) has the characteristics of drift effect of delayed neutron precursors (DNP), direct heating of coolant and moderator cooled by fuel salt under most conditions, which bring significant differences from traditional reactors in dynamics calculation. To deal with the unique dynamics characteristics of MSR, a specific three-dimensional spatial dynamics code – TMSR3D has been developed, in which the fourth order standard nodal expansion method and the exponential transformation method are implemented to solve the neutron diffusion equations and the neutron kinetics equations respectively, the parallel multi-channel thermal hydraulics (TH) model is adopted to take into account the feedbacks of local temperature to group constants, and a convection term is introduced to the traditional balance equations for DNP to consider the influence of fuel salt flow. Besides, the least square fitting method is employed to parameterize the few-group homogenized parameters generated by the lattice code DRAGON5. The 3D-LRA core benchmark is first used to verify TMSR3D for solid-fueled reactor problem. Afterwards, the experimental data of the Molten Salt Reactor Experiment (MSRE) collected in the European project MOST are simulated, which includes the transients perturbed by protected fuel pump start-up and coast-down at zero power, and the natural circulation experiment. The numerical results indicate that the developed code is capable of providing a reasonable description for the neutronics-TH coupling phenomena of graphite-moderated channel-type MSRs.