Dynamic Xenon Response in a CANDU-600 Reactor: A Simulation Study of Power Variations

Abstract This paper presents a comparative simulation study of xenon and fission product behavior in a CANDU-600 reactor core operating at nominal full power (100%) and an aging CANDU-600 core limited to 90% power due to end-of-life constraints. The analysis includes not only steady-state operating conditions but also transient phases such as shutdown and start-up, where xenon dynamics significantly impact reactivity management. Using theoretical reactor physics simulations, the study investigates xenon reactivity worth in both reactor conditions, with particular attention to the influence of fission product buildup and depletion. The simulations are supported by detailed evaluations of the reactivity compensation provided by the Liquid Zonal Controllers (LZCs), Adjuster Banks and Mechanical Control Absorbers (MCAs). The results highlight that while the 90% power core experiences reduced xenon production, it exhibits higher sensitivity to xenon-induced reactivity swings, particularly during power maneuvers and recovery from shutdown. The total reactivity worth of xenon, in conjunction with the control mechanisms, is quantified throughout the operational cycle. The findings reveal a tighter reactivity balance and reduced control flexibility in the aged core, emphasizing the increasing operational constraints as the reactor approaches end-of-life. These insights are critical for refining control strategies, ensuring safe operation, and optimizing performance across the full power range and operational scenarios of CANDU reactors.