Dynamic Simulation & Control of a Supercritical CO2 Power Conversion System for Small Light Water Reactor Applications

by Shih-Ping Kao, Jonathan Gibbs & Pavel Hejzlar
Massachusetts Institute of Technology

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Strategies to control a supercritical CO2 (S-CO2) power conversion system (PCS) have been investigated for light water reactor applications. Due to sharp changes in density and thermal properties near the pseudo-critical region, controlling the S-CO2 Brayton cycle presents unique challenges in nuclear power applications. A dynamic simulation code (SCPS), based on real-gas and momentum integral models, has been developed at MIT to evaluate control strategies for a small pressurized light water reactor equipped with a compact S-CO2 PCS. The NIST REFPROP subroutines and tables were integrated with the code to evaluate the CO2 properties at each timestep. The single-shaft, S-CO2 PCS consists of a radial compressor and turbine power train and three HEATRICTM Printed Circuit Heat Exchangers (PCHE) used as intermediate, recuperator, and pre-cooling heat exchangers. The primary system is that of a scaled-down commercial PWR. The simulation results show an oscillatory heat transfer behavior near the pseudo-critical region inside the precooler, similar to that observed in an experiment conducted by the Seoul National University. Consequently, the control programs were developed to maintain compressor inlet conditions away from and above the pseudo-critical region, thus avoiding heat transfer oscillations and compressor surge instabilities. An integrated control system, which couples the reactor power control with turbine throttle and bypass control, has been developed and shown to successfully control a small pressurized light water reactor coupled to a compact S-CO2 PCS for a wide range of operational transients.