Aimed primarily at regulatory bodies and the operating organizations of nuclear power plants, this Safety Guide provides recommendations on controlling activities relating to modifications to nuclear power plants. It covers modifications relating to plant configuration and to the operating organization, as well as temporary modifications. The responsibilities of the operating organization for the design, safety assessment and review, control, implementation and testing of these modifications are also within the scope of this Safety Guide as are the repair and replacement of equipment and components as part of the maintenance of the plant leading to new components.