Thermodynamic Study On Supercritical Carbon Dioxide Brayton Cycle For Nuclear Power Generation System

With the proposal of low carbon economy,the proportion of new energy in energy consumption structure is increasing,and nuclear power generation technology is developing rapidly.As the most mature reactor type in the fourth generation reactor,the sodium cooled fast reactor nuclear power plant has gradually met the requirements of commercialization.However,there are many safety problems in the heat transfer process.The contact between high temperature sodium and water could produce severe chemical reactions,which could result in the leakage of radioactive sodium.To avoid this problem,an intermediate loop between radioactive sodium and steam generator needs to be added.Because of higher thermal efficiency and higher safety,S-CO₂ Brayton cycle could be used as the thermal cycle of sodium cooled fast reactor.In this paper,the coupling system of sodium cooled fast reactor and the S-CO₂Brayton cycle was studied as follows:Firstly,the S-CO₂ Brayton cycle nuclear power generation system with three different cycle structures of simple recuperation,split recompression and split expansion was established,and the thermodynamic analysis was carried out.For the simple regenerative system,the influence of the initial parameters of the cycle on the system performance was studied.It was found that the system had the highest thermal efficiency when the minimum temperature and pressure of the cycle were near the critical parameters of CO₂.Based on the simple recuperation system,the effects of parameters such as the split ratio on the performance of the split recompression and the split expansion systems were mainly studied,and the optimal split ratios of the two systems were 0.36 and 0.43,respectively.Comparing the maximum thermal efficiency of the three systems under the same working condition,the thermal efficiency of the split-flow recompression cycle was the largest.Then,reheat split recompression S-CO₂ nuclear power generation system was proposed.The effects of split ratio,maximum circulating pressure and temperature on the system performance were studied,and the optimal operating conditions of the system were obtained.Compared with the single loop of BN-800 sodium cooled fast reactor,the electric power of the system was increased by 9.5%under the optimal operating conditions.Under the optimal working conditions,the mixed gas based on CO₂ was used as the working fluid for the study.By changing the type and mass fraction of the added gas,it was obtained that the addition of Xe could improve the thermal efficiency of the system,and the thermal efficiency increased by1%when the mass fraction of Xe was 20%.Subsequently,the exergy analysis of the reheat split recompression system were carried out,and the effects of the maximum temperature and pressure of the cycle,split ratio,turbine isentropic efficiency and compressor isentropic efficiency on the exergy loss and exergy efficiency of the equipment were studied.It was obtained that the exergy efficiency of the cooler was the smallest,and its lifting space was the highest.Finally,the mathematical model of the S-CO2 nuclear power generation system with optimal performance was established,and the Simulink model was constructed.The dynamic changes of the main parameters of the system could be obtained by simulation,which provided a reference for the research of S-CO2 Brayton cycle and sodium cooled fast reactor coupling nuclear power generation system.