A new concept of nuclear fuel cycle system for the fast reactors was proposed. The concept is mainly composed of a reprocessing and separation system based on hybrid microcapsules containing extradant, a remote fuel fabrication system for carbide coated particle fuels and a gas-cooled fast reactor. The gas-cooled fast reactor system features a fast-neutron-spectrum helium-cooled reactor and closed fuel cycle to be able to have sustainable energy resources in future. The feasibility study of the concept has been performed from the viewpoints core performance, radioactive waste reduction, separation technology, fabrication technology, etc. It was shown that the new concept of nuclear fuel cycle system including the gas-cooled fast reactor is very attractive to the future energy supply system in this study.