Abstract: The design of the nuclear power plant thermodynamic system is to increase the economy of the plant while maintaining or improving safety margins. The economy of the plant is influenced by many factors including technical maturity, equipment maturity and thermo-economy of the thermodynamic system. To determine the optimum configuration of re-heater, using the Russian 800 MW sodium cooled fast reactor thermodynamic system as a reference, the physical model of re-heater and vertical moisture separator re-heater based on thermal equilibrium method was built and a thermo economic analysis code was developed. To assess the development status of this code, benchmark calculations were performed with the Russian design values. Based on the reference system, the scheme of different re-heater arrangements and the scheme of different enthalpy rises were discussed. It is found that the equal enthalpy drop distribution method is of the best thermo-economy.