Abstract: A reactor of a nuclear plant encloses a core having a plurality of fuel elements and a number of control rods. Each fuel element includes a plurality of fuel rods each including a cladding and nuclear fuel enclosed in an inner space of the cladding. Each control rod is insertable to and extractable from a respective position between or in respective fuel elements to influence the effect of the reactor. A method for operating the reactor includes operating the reactor at a normal effect during a normal state, monitoring the reactor for detecting a defect on the cladding of any fuel rod, reducing the effect of the reactor after the detection of a defect, operating the reactor during a particular state during a time period during which the reactor at least during a part time is operated at the reduced effect in relation to the normal effect, and extracting the inserted control rods after the time period for continuing operation of the reactor at substantially the normal state.