Development of transient thermal-hydraulic analysis code for SCO2-cooled reactor coupled with Brayton cycle and its application

•Complete set of transient thermal-hydraulic analysis models is developed based on Modelica language for the system of SCO2-cooled reactor coupled with Brayton cycle.•By comparing with the results of FROBA-SCO2, SACOS-SCO2, KAIST and TRA-SCR, the model developed in this paper is proved to be precise.•Reactivity insertion accident without protection of the SCO2-cooled reactor is simulated and analyzed. The thermal-hydraulic characteristics of the core and other components in MMR system are obtained.•According to the results and analysis, MMR system has certain inherent safety and the developed Modelica model can simulate the system for more detailed transient performances under different accidents. Supercritical carbon dioxide (SCO2) direct cycle gas fast reactor system has attracted lots of attention from different institutions worldwide. Most of the research on SCO2-cooled reactors put emphasis on the design and optimization of core parameters, but few on detailed thermal-hydraulic analysis for SCO2-cooled reactors coupled with Brayton cycle. To supplement the lack of research in this area, a program based on Modelica language is established for transient simulations of SCO2-cooled reactor system. Then, the results of developed Modelica model are compared with code results obtained by GAMMA+, FROBA-SCO2 and SACOS-SCO2, which achieves good agreement. Based on the developed models and codes, thermal-hydraulic characteristics of SCO2-cooled reactor coupled with simple Brayton cycle under the conditions of reactivity insertion accident are studied. According to the validation and transient simulations for different reactivity insertion accidents, Modelica model developed in this paper shows great ability in getting more detailed transient performance of coupled SCO2-cooled reactor system under different working conditions.