The micro-high temperature gas cooled reactor (Mi-HTR) uses Tri-structural iso-tropic (TRISO) particle as fuel, helium gas as coolant, and graphite as moderator and structural material. The reactor adopts complete passive residual heat removal technology and is inherent security. The usage of the Mi-HTR is megawatt-level micro nuclear power plant. Because of the using of hexagonal prism graphite core, the dynamic characteristics of the Mi-HTR are different from large scale high temperature gas cooled reactors and pressurized water reactors. Therefore, the accurate and reliable reactor dynamic characteristics analysis are of significance for the design of the Mi-HTR control system. The neutron kinetics model of the Mi-HTR is built based on the point reactor kinetics with the reactivity feedback mechanism. The core thermal-hydraulic model of the Mi-HTR is built based on the fundamental conservation laws. By coupling the two models, a lumped-parameter model of the Mi-HTR is established. In order to obtain an accurate transfer function model for subsequent control system design, the mechanism model is linearized based on perturbation theory, and then the transfer function model with different inputs and outputs is obtained through Laplace transform.
The developed nonlinear model is implemented on MATLAB/Simulink. By introducing a variety of disturbances, the simulation results of transient responses are presented, which show that the static precision of the dynamic model is satisfactory, and the trend of the transient responses is consistent with the physical laws. The obtained transfer function model and the nonlinear model are introduced with the same disturbances, and the simulation results show that the responses of transfer functions are consistent with those of the nonlinear model. Therefore, the transfer function model can be utilized to control system design for the Mi-HTR.