Modeling a generic Pebble Bed High-Temperature Gas-Cooled Reactor to perform load-following using Simulink

To meet future energy demand, while producing safe, reliable, and carbon-free energy, nuclear reactors will be needed. Before operating these systems, designers must be sure that they can operate these systems efficiently and safely in a variety of different scenarios. To have the capability of evaluating different control approaches given component degradation for a Pebble-Bed High-Temperature Gas-cooled Reactor (PB-HTGR), a system model consisting of the System Analysis Module (SAM) coupled to Simulink is developed. SAM is used to model the dynamics of the PB-HTGR core and Simulink is used to model the Once-Through Steam Generator (OTSG), Balance of Plant (BOP), and the control system. To increase computational efficiency, the SAM PB-HTGR model is replaced with a Feedforward Neural Network (FFNN) surrogate that was successful in explaining over 99.8% of the variance seen in the data. The control system uses Proportional-Integral-Derivative (PID) controllers to successfully perform a 100%-25%-100% load-following scenario with a maximum ramp rate of 5%/min. When performing load-following scenarios, the PB-HTGR model can also simulate the system response to degradation of the pumps, turbine, and OTSG. With any of the components within this system, their performance will deteriorate over time and load-following will become more difficult to perform. With no intervention, these degradation mechanisms will result in the decrease of overall system electrical output and the system approaching its safety limits. To address these challenges, the PB-HTGR Simulink model aims to provide an environment where different control schemes can be tested in the presence of component degradation to find better control schemes and maintain safety margins.