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Sodium-cooled fast reactor (SFR) is one of the most promising reactors among the six Gen-IV reactor systems due to its significant advantages in close fuel cycle, comprehensive technology foundations and operation experiences. China is designing and constructing a demonstration SFR, in which, to ensure the reactor passive safety, a direct reactor auxiliary cooling system (DRACS) with the inter-wrapper flow is proposed as the decay heat removal system. Xi'an Jiaotong University is in charge of the DRACS analysis code development. The physical models in the DRACS are extracted and the numerical models for each component are established. The Gear method and the SIMPLE method are adopted as the primary solution algorithm. The code is developed and validated by EBR-II and PHENIX benchmarks, the results of which indicate that the code can predict experimental results very well.

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It's increasingly clear that the existence of thermodynamic equilibrium is an exception rather than the role in SF₆/N₂ thermal plasmas. We intended to investigate the dominant physicochemical properties of SF₆/N₂ thermal plasmas at 4  atm from 12000 K to 1000 K with considering the thermal non-equilibrium. A two-temperature chemical kinetic model containing all the available reactions is developed. The temperature difference between the electron and the heavy species is defined as a function of the electron number density. The molar fractions of species are compared to the equilibrium composition predicted by Gibbs free energy minimization. By analyzing the main reactions in the generation and loss of a dominant species, the chemistry set is simplified and characterized by a few species and reactions. Then, the dominant physicochemical properties are captured and the computing time of complicated chemical kinetic model is dramatically shortened at the same time.