[en] The feasibility Study on Commercialized Fast Reactor (FR) Cycle System Phase-II was commenced on April 1, 2001, in order to clarify a few promising concepts for commercialization from among the candidates of FR systems and fuel cycle systems that were screened out in Phase-I, and to present the outline of the onward plan for Phase-III. In FY 2002, to obtain engineering data for the feasibility assessment of principal technologies and clarification of candidate concepts for commercialization, important technologies were developed. For the FR system, the core high burn-up was studied by increasing the core conversion ratio. Burn-up of the entire core including blanket fuel was expected to be about 100GWd/t for the sodium-cooled reactor and the lead-bismuth reactor, and about 50GWd/t for the water-cooled reactor. In terms of the key technology development, the engineering data was obtained by the tests related to the flow stabilization in the upper plenum of the reactor vessel for the sodium-cooled reactor, the material corrosion for the lead-bismuth cooled reactor and the coolability of the dense core for the water-cooled reactor. With regard to the fuel cycle systems, detailed system designs were created considering the material handling technologies, remote-controlled handling and repair, etc. In terms of key technology development, the extraction of U/Pu from spent fuel verified by the direct extraction method at the CPF (hot cell) at Tokai Works. The technical feasibility of the simplified solvent extraction method and simplified pelletizing method, which is important for the technical feasibility, was confirmed. (author)