A megawatt-class nuclear power system has been developed by coupling a heat pipe reactor with a supercritical carbon dioxide (S-CO₂) Brayton cycle. This system offers advantages in terms of high safety, power density, and compactness.

This study aims at the operation characteristics of this power system with high efficiency and compactness.

The coupling code of a self-developed heat pipe reactor transient analysis code, Transient Analysis code for heat Pipe and AMTEC power conversion space Reactor power System (TAPIRS), and supercritical carbon dioxide Brayton cycle transient analysis code (SCTRAN/CO₂) were utilized to analyze the open-loop dynamic characteristics under conditions of reactivity disturbance, load disturbance, cooling water temperature disturbance, and cooling water mass flowrate disturbance. Then, the control system was designed. On this basis, three load variation operation conditions, i.e., linear load variation, stepped load variation, and load rejection, were simulated and analyzed.

The simulation results show that the rotational speed of the new nuclear power system is sensitive to the disturbances and needs to be controlled. The bypass flowrate increases under low load conditions, hence the flowrate of the compressor needs to be controlled as well. The system can adjust the load from 0% to 100% at a rate of 6% FP (full power)·min^-1. It is capable of implementing stepped load changes, although it experiences slightly more pronounced fluctuations. Under load rejection conditions, the stabilization time might be prolonged, but it will eventually stabilize with all parameters remaining within safe limits.

This study provides a reference for the conceptual design of new nuclear power systems with high efficiency and compactness.