A Study on Xenon Estimation During Load-Follow Operation Using Sliding Mode Observer in APR1400 for A Predictive Soluble Boron Control

Abstract

During daily load-follow operations (DLFOs) in nuclear reactors, xenon concentration varies with power level, necessitating adjustments to the soluble boron concentration via dilution or boration. Since xenon cannot be directly measured within the reactor, this study introduces the use of a sliding mode observer (SMO) to estimate xenon concentration on the fly during the DLFO. Based on these estimates, the necessary boron concentration adjustments are calculated using a control algorithm (Mode-K +) that integrates data on the reactor’s chemical control system, xenon, and boron worth. This study focuses on the APR1400 reactor’s initial cycle and demonstrates a high degree of accuracy between the estimated xenon concentrations and reference values derived from KANT’s in-house 3D time-dependent xenon model. The integration of the SMO with the load-follow operation control algorithm represents a significant advancement by providing reactor operators with precise boron adjustment information. This precision minimizes unnecessary control rod movements, thereby reducing the risk of axial or radial power peaking, a critical factor for maintaining reactor stability and safety. Additionally, this approach optimizes the boron dilution process by accurately timing and controlling the volume of demineralized water introduced into the system. This not only ensures the effective execution of load-follow operations but also significantly reduces the volume of liquid radioactive waste produced. The analysis was conducted using a two-step procedure: cross-sectional evaluation via the Serpent 2.2.0 continuous energy Monte Carlo code, followed by whole-core calculations to generate lumped parameters using KANT. This methodology offers a robust and novel solution for enhancing the safety and efficiency of nuclear reactor operations during load-follow scenarios.