[en] Major activities and events concerning YAYOI (a fast neutron source reactor at the Nuclear Engineering Research Laboratory of the University of Tokyo) during fiscal 1975 and 1976 are summarized. In this period, the reactivity-pulse-operation of the reactor was approved and started. This report presents all efforts for obtaining the license and preliminary performance tests. Major events during this period are weekly recorded and tabulated in a list. Major items included in this report are; details of major events, list of documentation prepared for licensing, revision of safety prescription, submission of preliminary inspections, the history of the reactor operation, and the detail of the expences. (Aoki, K.)