A small modular fast reactor is thought to be one of the solutions to meet future energy security with low research and development (R&D) risk. In the present study, a new small reactor concept for a modular power source is proposed. A minimum configuration with a compact reactor vessel, one-loop main cooling system, and simple fuel-handling system is adopted, enhancing cost reduction. In the present one-loop main cooling system, there are double electromagnetic pumps in series considering pump failure. To show the reliability of the one-loop main cooling system, pipe-break transient analyses have been carried out. In addition, the construction cost of a set of a first-of-a-kind reactor and small fuel cycle plant is evaluated to show the economical potential at the demonstration stage. A major advantage of the present concept is that the demonstration reactor and fuel cycle plant can be directly appropriated for first commercial modules and the power plant can easily increase its capacity adding reactor and electrorefiner modules. Commercialization of the nuclear fuel cycle fusing the present modular concept is thought to reduce R&D risk since the total budget for demonstration is small and the facilities for demonstration are directly appropriated to commercial use.