In Japan, the effort to develop the large fast breeder reactors is still continuing in the various technical fields in order to realize the safe, economic, uraniumresource saving, environmental burden-reducing, and non-proliferating FBR plant concepts, under the name of “FBR Cycle Feasibility Study” that is strongly related to the international cooperation of Generation-IV project. The improvement and application work of nuclear data are being performed in the context of the national strategy. The purpose of the present paper is to introduce the recent status of nuclear data application to fast reactor cores in Japan. The contents are classified into three categories; one is the development of group constants and analytical tools related to nuclear data, the next is the consistent evaluation of the Japanese Evaluated Nuclear Data Library (JENDL) by the fast reactor experimental database, and the last is the improvement of prediction accuracy and application to fast reactor design study.

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