Evaluation of load following control strategy for heat pipe-cooled microreactor coupled with closed Brayton cycle system

Heat pipe-cooled reactors (HPCRs), with their straightforward and compact design and inherent safety features, are considered a promising option for mobile nuclear power sources. However, the coupling between the HPCR and the energy conversion system complicates load tracking control. In this study, a comprehensive dynamic model of an HPCR coupled with a closed-air Brayton cycle (CABC) is developed. This model integrates a neutron kinetics point reactor model, a thermal resistance network model for the heat pipe, and a CABC model representing the power conversion system. To achieve effective load tracking, a control scheme for the Brayton cycle power is proposed, combining turbine bypass control with inventory control. The system's response to load variations, from 100 % full power (FP) to 50 % FP at a rate of 5 % FP/min, is analyzed, considering reactor power self-regulation. The results indicate that the reactor power exhibits an overshoot of −4.36 % and stabilizes after 2100s, while the fuel average temperature fluctuates within ±4.6 °C and stabilizes at 2240s. Building on the dynamic performance of the HPCR-CABC system, a reactor power control scheme is developed by adjusting control drums to introduce external reactivity. This scheme successfully controls reactor power at a steady state within 720s, without fluctuation. However, the fuel average temperature fluctuates by more than 10 °C, stabilizing after 9450s. To improve control effectiveness, a temperature correction channel is incorporated into the reactor power control system. As a result, the fuel average temperature fluctuates within ±0.3 °C and stabilizes at the design value of 699.4 °C within 860s. Compared to previous control schemes, the improved cascade reactor power control scheme results in a shorter stabilization time for the fuel average temperature. To assess the adaptability of the proposed HPCR-CABC coordination control strategy, simulations are conducted for load reductions from 100 % FP to 80 %, 60 %, and 40 % FP at a variation rate of 20 % FP/min. The results demonstrate that the proposed HPCR-CABC coordination control strategy exhibits strong load-following capability.