[en] The experimental fast reactor ''Joyo'' started the first cycle 50 MW operation with its core composed of 71 core fuel subassemblies from October 27, 1978, and finished it on December 11, 1978. One of the core fuel subassemblies used for the 50 MW operation was carried into the Fuel Monitoring Facility for the post-irradiation examination. The construction of the building for spent fuel storage and cooling, the installation works of air conditioning and electrical equipments for this building, and the construction of large storage for equipments were completed. Concerning the prototype fast breeder reactor ''Monju'', the Constructive Preliminary Design (2) was started. The analysis of decay heat has been completed as the material preparation for the Safety Licensing by the Committee. As the developmental works of codes, the probability evaluation code for the integrity of fuel elements, the analytical code for core thermal hydrodynamic transient characteristics, the core operation planning code and the improvements of PLANET code, D-CHAIN code and ORIFS code, etc. are under way. The government agency and the prefectural offices are presently conducting the environmental examination around ''Monju''. The related data were opened to public inspection from October 20 to November 8. The explanation meetings were held on November 14 and 27, 1978, at Tsuruga City. The preliminary design (4) of the demonstration fast breeder reactor was started. The situations of progress of the reserch and development works on reactor physics, structural components, instrumentation and control, sodium technology, fuel and structural materials, safety and steam generators are reported. (Nakai, Y.)