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Organic Rankine cycle (ORC) and supercritical CO 2 (sCO 2) Brayton cycle are two key and competition technology routes as the power cycle of Lead–Bismuth micro-reactor (LBMR). However, few studies focus on the comparison of thermodynamic and economic performance between ORCs and sCO 2 cycles in nuclear micro-reactor. The objectives in this study are to perform parameters analysis and techno-economic comparison in ORCs and sCO 2 cycles with various configurations as the power cycle of LBMR, so as to provide the technical support for the selection of power cycle and its operating conditions in different scenarios. Several high/low-temperature working fluids are screened for ORCs in view to achieve high net efficiency (η th) and low electricity production cost (EPC). Multi-objective optimization is performed to solve the trade-off between η th and EPC , and then to compare the comprehensive performance of various cycles from thermodynamic, compact and economic aspects. Results show that, the η th and EPC of ORCs are comparable or superior to that in sCO 2 cycles when the two cycles have similar structures (simple/regenerative). Among the ORCs, the cascade ORC with two-side regeneration using N -Dodecane/Pentane as working fluid pair has the best performance. In all cycles, recompression sCO 2 cycle performs best, but only when the heat source temperature is higher than 460 °C, the performance of the recompression sCO 2 cycle are overall better than the cascade ORC. • Techno-economic comparison of various power cycles for LBR are conducted. • Several high/low-temperature fluids are screened in different configurations of ORC. • N -Dodecane/Pentane is the best working fluid pair for the cascade ORC2. • The η net and EPC of ORCs are slight superior to sCO 2 cycles with similar structures. • The η net and EPC of recompression sCO 2 cycle are both better than ORC when t s > 460 °C. [ABSTRACT FROM AUTHOR]