A fault-tolerant control method for microreactor control drums based on fault severity

Control drums are the core actuators for reactivity regulation in microreactors, and their reliability is directly related to reactor safety. Faults in control drums may lead to reactivity excursions, necessitating the design of appropriate fault-tolerant control methods to maintain safe reactor operation to the greatest extent possible. To this end, this paper proposes an active fault-tolerant control method based on fault severity assessment. First, based on the dynamic response characteristics of the actual and commanded positions of control drums, a diagnostic rule base covering four typical fault types—stuck, continuous positive deviation, continuous negative deviation, and gain error—is constructed to achieve online fault detection and identification. Subsequently, differentiated fault-tolerant control strategies are designed according to fault severity levels: a “rapid isolation + compensatory control” strategy is adopted for high-severity continuous positive deviation faults; a “maintain current state + progressive compensation” strategy is employed for medium-severity continuous negative deviation faults; and a “fault isolation + redundant compensation” strategy is applied to low-severity stuck and gain error faults. Simulation results demonstrate that the proposed method can effectively identify fault modes while maintaining load-following capability and ensuring reactor safety. Under all four fault conditions, both nuclear power and average fuel temperature can recover to pre-fault levels within 260 s, with the average fuel temperature remainingwithin safety limits throughout. The average fuel temperature never exceeds 966.4 K, leaving a minimum margin of 806.6 K to the 1773 K fuel temperature limit adopted for this reactor. This method requires no additional hardware investment and provides an effective solution for fault tolerance of control drums in micro heat pipe-cooled reactors.