Potential sodium–CO2 interaction of a supercritical CO2 power conversion option coupled with an SFR: Basic nature and design issues

Abstract

The supercritical CO2 Brayton cycle option for energy conversion in a sodium-cooled fast reactor (SFR) has recently received a great deal of attention due to highly reliable system design features that make it essentially free from risk of a sodium–water reaction in a traditional Rankine cycle power conversion. Although this novel approach will yield significant improvements in overall plant safety and energy utilization, it raises the risk of pressure boundary failure and consequent sodium–CO2 interaction. Since an understanding of the interaction mechanism is directly relevant to safety issues for the advanced SFR design, the kinetic behavior of sodium–CO2 interaction and its basic nature were investigated in this study. Experiments were performed for sodium temperatures ranging from 200 to 600°C. The results indicated that the reaction kinetics over the sodium temperature range of 300–550°C depends heavily on the temperature but is not sensitive to the velocity of CO2 flowing over the gas–liquid reacting interface explored in this study. The rate of the chemical reaction was determined by measuring the gas concentration of the CO/CO2 mixture, and a two-zone reaction model was proposed with a threshold temperature of 460°C. The kinetic parameters, i.e., the activation energies according to reaction zones, were obtained experimentally and the corresponding model parameters were identified. Finally, practical design and safety issues regarding a wastage scenario and the potential plugging of faulty heat exchanger channels were also addressed.