Supercritical CO2 (sCO2) cycles are considered as a promising technology for next generation concentrated solar thermal, waste heat recovery, and nuclear applications. Particularly at small scale, where radial inflow turbines can be employed, using sCO2 results in both system advantages and simplifications of the turbine design, leading to improved performance and cost reductions. This paper aims to provide new insight toward the design of radial turbines for operation with sCO2 in the 100–200 kW range. The quasi-one-dimensional mean-line design code topgen is enhanced to explore and map the radial turbine design space. This mapping process over a state space defined by head and flow coefficients allows the selection of an optimum turbine design, while balancing performance and geometrical constraints. By considering three operating points with varying power levels and rotor speeds, the effect of these on feasible design space and performance is explored. This provides new insight toward the key geometric features and operational constraints that limit the design space as well as scaling effects. Finally, review of the loss break-down of the designs elucidates the importance of the respective loss mechanisms. Similarly, it allows the identification of design directions that lead to improved performance. Overall, this work has shown that turbine design with efficiencies in the range of 78–82% is possible in this power range and provides insight into the design space that allows the selection of optimum designs.