[en] The purpose of this project, 'Development of design technology for a dual-cooled fuel structure' launched from March 2007, is to develop the major structural components such as a fuel rod support structure, guide thimbles and an instrumentation tube, and top and bottom end pieces, which are compatible with the OPR-1000 reactor internals. To this end, the design criteria, functional requirements and necessary technical issues for satisfying them were investigated during the first year and published as a conceptual design report. In this second year, the methods to resolve the issues and relevant candidate shapes were derived, which is published as a present fundamental design report. As for some resolutions, it was suggested to move the present support location in a grid cell towards the cross points of the straps; to form a horizontal plate for holding the sectioned fuel rods. In the case of guide thimbles of a coaxial tube form, the drop time was found to be satisfied through a commercial code calculation. The flow areas of the top and bottom end pieces' flow plates increased somewhat compared with those of a conventional fuel, which may compensate the increased pressure drop caused by a narrow gap between the dual-cooled fuel rods. From the currently suggested component shape, total weight of a fuel assembly is different from that of the conventional one by -1.7% ∼ +3.7% only, from which it is regarded that the compatibility with the OPR-1000 reactor internals is satisfied with the present design of a dual-cooled fuel