Enhanced Flexibility of PWRs (Mode A) Using an Efficient NMPC-Based Boration/Dilution System

This paper presents a novel automatic borationdilution system aimed at Pressurized Water Reactors which were initially designed for base load operation (most often with the so-called mode A core control system). The main objective is to enhance maneuvering capabilities of already-installed plants by ensuring proper regulation of the axial power distribution during power variations. No substantial modification of the on-site instrumentation and control equipment is required to implement this new control system. In addition, this device can be easily converted into a real-time aid predictive system to help plant operators control the axial offset of the reactor core. Unlike currently available open-loop simulators, a key feature of this control-based system is to periodically benefit from on-site measurements to counteract model discrepancy and unexpected disturbances.The proposed system relies on Nonlinear Model Predictive Control to efficiently control the axial offset of the reactor core with respect to hard actuator constraints. For this purpose, a simplified multi-point core kinetic model of the reactor was developed. This model is then reduced using singular perturbation theory to allow quick computation of the NMPC control law as well as full-state estimation at each recalculation instant. Nevertheless, the reduced model still provides a reasonable level of accuracy in regard to our control objective. Finally, various MATLAB^®/Simulink^® simulation scenarios were tested to tune the NMPC controller before being successfully validated on a realistic full-scale nuclear power plant simulator. Effectiveness of the control strategy is supported by excellent validation results.