Adoption of nitrogen power conversion system for small scale ultra-long cycle fast reactor eliminating intermediate sodium loop

•N2 power conversion system for both safety and thermal performance aspects.•Sensitivity studies of several controlled parameters on N2 power conversion system.•The elimination of the intermediate loop increased the cycle thermal efficiency.•The elimination of the intermediate loop expects economic advantages. As one of SFRs, the ultra-long cycle fast reactor with a power rating of 100MWe (UCFR-100) was introduced for a 60-year operation. As an alternative to the traditional steam Rankine cycle for the power conversion system, gas based Brayton cycle has been considered for UCFR-100. Among Supercritical CO2 (S-CO2), Helium (He), Nitrogen (N2) as candidates for the power conversion system for UCFR-100, an N2 power conversion system was chosen considering both safety and thermal performance aspects. The elimination of the intermediate sodium loop could be achieved due to the safety and stable characteristics of nitrogen working fluid. In this paper, sensitivity studies with respect to several controlled parameters on N2 power conversion system were performed to optimize the system. Furthermore, the elimination of the intermediate loop was evaluated with respect to its impact on the thermodynamic performance and other aspects.