The realization of a zero-carbon electricity system is of vital importance to CO2 reduction in an energy system, and nuclear power is expected to contribute to this much more than the intermittent, complicated, and costly renewable energy in the future in Japan. Therefore, in the present study, a future zero-carbon electricity system based on 100% nuclear power was proposed in Japan. The feasibility of the system was studied in terms of the reliability of fluctuations of both the daily and seasonal electricity demand and supply using an hour-by-hour computer simulation. The simulation provided a detailed system design and real-time operation information for the electricity system based on hourly data series of electrical load, nuclear power output, and electricity storage. The obtained results show that the proposed nuclear-power-based zero-carbon electricity system is technologically feasible with the help of EV batteries and hydrogen for daily and seasonal electricity storage, respectively, and smart control technologies are necessary to operate the whole system. Finally, key issues relating to the implementation of such a system were discussed to highlight the need for continued research.