This Safety Requirements publication establishes the requirements to be met to ensure the safe operation of nuclear power plants. This publication supersedes Safety Series No. 50-C-O (Rev. 1), Code on the Safety of Nuclear Power Plants: Operation (1988). It restructures the code in the light of the Safety Fundamentals publication, Safety Series No. 110, The Safety of Nuclear Installations (1993), and Safety Series No. 115, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (1996). It introduces new topics to reflect current international practices and new concepts and technical developments.