Abstract: Micro nuclear power systems have attracted considerable attention for energy supply in remote regions due to their advantages of high energy density, autonomous operation capability, and modular deployment characteristics. However, the design of their power conversion systems is constrained by multiple engineering requirements, including limited heat source temperature, transportation dimensions, system mass, and economic feasibility. Therefore, achieving a reasonable balance among thermodynamic performance, economic cost, and system compactness is essential for the development of compact nuclear power conversion systems. In this study, a supercritical carbon dioxide (sCO₂) Brayton cycle system coupled with a micro lead-bismuth-cooled nuclear reactor was investigated under a 450 ℃ heat source condition and the spatial constraint of a single ISO 40 ft container module. Two advanced cycle configurations, namely the pre-compression Brayton cycle (PCBC) and the recompression Brayton cycle (RCBC), were selected for comparative analysis. A steady-state system model was developed, incorporating thermodynamic analysis, exergoeconomic evaluation, and component mass estimation. The effects of key design parameters, including turbine inlet temperature, minimum cycle pressure, cycle pressure ratio, pre-compression coefficient, and split ratio, on system exergy efficiency, unit electricity exergy cost, and exergoeconomic power density (EPD) were systematically investigated. To reduce the computational burden during multi-objective optimization, an artificial neural network (ANN)-based surrogate model was established based on the thermodynamic simulation results. The non-dominated sorting whale optimization algorithm (NSWOA) was subsequently employed to obtain the Pareto optimal solutions considering exergy efficiency, unit electricity exergy cost, and EPD simultaneously. Multi-attribute decision-making methods were further applied to identify the preferred design solutions under different performance priorities. The results demonstrate that the RCBC configuration provides higher thermodynamic performance potential, with optimized exergy efficiency ranging from 63% to 67%, owing to its improved heat recovery capability. In comparison, the PCBC configuration exhibits advantages in economic performance and system compactness due to its relatively simpler compression structure and lower equipment requirements. The optimization results reveal evident trade-offs among thermodynamic efficiency, economic cost, and system mass, indicating that no single configuration can simultaneously achieve the optimal values of all evaluation objectives. The proposed analysis framework provides a comprehensive approach for cycle configuration selection and parameter optimization of micro nuclear power conversion systems under space-constrained deployment conditions.