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For the realization of safe and economical fast reactor (FR) plants, the Japan Nuclear Cycle Development Institute (JNC) and Japan Atomic Power Company (JAPC) are cooperating on a research project titled “Feasibility Study on Commercialized FR Cycle Systems.” To certify the design concepts and validate their structural integrity, the research and development of the “Fast Reactor Structural Design Standard (FDS)” is recognized as being an essential theme. FDS considers the general characteristics of FRs and the design requirements for their rationalization. Three main problem areas related to research and development issues were identified by FDS. The first is “refinement of failure criteria,” which takes characteristic design conditions into account. The next is the development of “guidelines for inelastic design analysis” in order to predict the elastic plastic and creep behaviors of high-temperature components. Finally, efforts are being made toward preparing “guidelines for thermal load modeling” for FR component design where thermal loads are dominant. Their research plans and current status are explained.

Effects of proton irradiation on the reactor pressure vessel steel (RPVS), A533B cl. 1 have been investigated by means of positron lifetime and Vickers hardness measurement in comparison with those of the iron-copper model alloys. The specimens were irradiated with 1 MeV proton up to a fluence of 3 × 1017 ions/cm2 (0.2 dpa, displacement per atom, at a peak) at temperature below 80°C. The recovery behavior of the irradiation effects was also investigated during isochronal annealing for 30 min with a 25°C step from 100°C to 650°C. By positron annihilation technique, it was recognized that microvoids, which consist of about 5 vacancies with the number density of the order of 1016 /cm3, were formed by the irradiation. The number of microvoids decreased after a low temperature annealing and completely annihilated at 250°C, although irradiation hardening still remained. A large portion of the hardening recovered by the annealing up to 300°C and almost annealed out at 450°C. Irradiation response and its recovery behavior of A533B RPVS were discussed compared to the result of Fe-based model alloys.