[en] The development of ATR and FBR is proceeding in Japan, to attain efficient utilization of nuclear fuel and to secure future supply of energy. The ATR is capable of operation with natural uranium, and its early realization is expected. The FBR is able to produce more fissile material than its consumption. As the prototype of the ATR, ''Fugen'' is moderated with D₂O and cooled with boiling light water, and the output is 165 MWe. It is expected to go critical in 1977. As for the FBR, the experimental ''Joyo'' and the prototype ''Monju'' are under development, and Pu-U mixed oxide is used as the fuel. They are cooled with sodium. The Joyo of 100 MWt will go critical in 1976, while the Monju of 300 MWe is still in design stage. (Mori, K.)