[en] As for the demonstration reactor following the prototype FBR 'Monju', Japan Atomic Power Co. has advanced the research on the design with the cooperation of the organizations concerned, and the technical development is in progress. In fiscal years 1990 and 1991, the outline design of the main systems, machinery and equipment of the top entry, loop type demonstration reactor and the technical evaluations of structural integrity, safety, operation, maintenance and others have been carried out, and its technical feasibility was confirmed. In this report, the features, the concept of the structure and the results of the technical evaluation of the top entry, loop type FBR are outlined. The course of FBR development so far is summarized. The designs of the whole plant, the core and fuel, the structure of the reactor, the machinery and equipment of the cooling system, safety and protection facilities and fuel handling system, and the technical evaluation of safety, structural integrity, confirmation test, operation and maintenance and economy are reported. (K.I.)