[en] Japan Nuclear Cycle Development Institute (JNC) and Japan Atomic Power Company (JAPC) launched joint research programs on structural design and three-dimensional seismic isolation technologies, as part of the supporting R and D activities for the feasibility studies on commercialized fast breeder reactor cycle systems. A research project by JAPC under the auspices of the Ministry of Economy, Trade, and Industry (METI) with technical support by JNC is included in this joint study. This report contains the results of the research on the structural design technology. The research scope was identified as (1) Study on Developing Program, (2) Study on 3-dimensional Entire Building Base Isolation System, and (3) Study on Vertical Isolation System for Main Equipment, and the results of this year's studies are summarized as follows. (1) Study on Developing Program. According to the comparison between the target spectra of the Case Study S2 and the spectra of the Taiwanese official recorded data of the Sep. 21, 1999 Chi-Chi Earthquake, it was found that the spectra of the Chi-Chi data were less than that of the Case Study S2. Then it is possible to use the Case Study S2 for the study on 3-dimensional isolation system. The performance requirements of the equipment/piping and building design for the middle scaled sodium and Lead-Bismuth cooling type FBR to the 3-dimensional seismic isolation devices was studied, and then the requirements for both design were superimposed and concluded as follows. The middle scaled sodium-cooling type FBR. Vertical frequency fv: <0.67 Hz, Vertical damping ratio hv: 20% for entire building base isolation. Vertical frequency fv: 1.0 - 3.0 Hz, Vertical damping ratio hv: 20% for vertical isolation of main components. The middle scaled Lead-Bismuth cooling type FBR. Vertical frequency fv: 0.667 - 1.0 Hz, Vertical damping ratio hv: 20 - 40% for entire building base isolation. (2) Study on 3-dimensional Entire Building Base Isolation System. The testing devices of 3 promising ideas, i.e., '3-dimensional base isolation system equipped with hydraulic mechanism', '3-dimensional seismic isolation devices with laminated rubber bearing and rolling seal air spring', '3-dimensional base isolation system with cable reinforcing air spring', were fabricated. The characteristic tests using above devices were also studied. (3) Study on Vertical Isolation System for Main Equipment. The 10 actual-sized coned disk springs were fabricated, and static tests were carried out for investigating the mechanical characteristics of those ones. The structural tests of the damping element for choosing the dimension of the element were carried out. The performance tests for the element, whose size were determined by above tests, were also carried out. Construction sequence on building the isolation device in the vertical isolation system. The information obtained through above tests and studies were reflected and revised in the seismic isolation design recommendation draft of the vertical seismic isolation design method. (author)