The possibility of a state, which has imported a fast reactor with closed fuel cycle enterprises, breaching the nuclear non-proliferation regime and secretly using the acquired equipment, technologies, and nuclear materials to originate nuclear weapons is discussed. It is assumed that the most likely development of events could be an importing state combining clandestine and overt scenarios: clandestine for the preparatory period of development of the non-nuclear components of a nuclear device, accumulation of experience and knowledge, and obtaining the required amount of weapons-grade nuclear material and overt for testing the developed device and its replication. Possible tools for detecting signs of breaching of a nuclear non-proliferation regime when IAEA safeguards are used in an importing state using information technologies are considered.