Study on the dynamic response mechanisms of a lead-bismuth fast reactor coupled with a transcritical CO2 power cycle

Abstract

The integration of a lead-bismuth fast reactor (LFR) with a transcritical CO₂ (T-CO₂) power cycle represents a promising offshore nuclear energy solution. Although prior research has advanced the primary and secondary circuits separately, their dynamic interactions under tightly coupled conditions remain insufficiently explored. This work establishes a dynamic system model to investigate bidirectional disturbance propagation and load-following coordination between the two circuits. Results indicate that reducing reactor power by 5 % and 10 % decreases secondary circuit output by 13.8 % and 28.4 %, respectively. Variations in secondary circuit parameters, such as pump speed and cold source temperature, alter the CO₂ mass flow rate and evaporator heat transfer, leading to temperature changes in the primary coolant. Through inherent temperature feedback, the reactor autonomously adjusts its power, demonstrating strong closed-loop coupling. Notably, pump speed has a greater influence on secondary circuit output than cold source temperature, contributing approximately 5.6 % more to the output work variation. During load following, adjusting only reactor power lowers both turbine inlet temperature and system efficiency. In contrast, coordinated adjustment of reactor power and secondary circuit flow maintains a more stable thermal state while adapting to load changes, improving average thermal efficiency by 2.1 % compared to the reactor-only strategy. This study clarifies key thermophysical coupling mechanisms in the LFR–T-CO₂ system and provides a valuable reference for the coordinated control of marine nuclear power systems under dynamic operating conditions.