METHOD OF OPERATING A NUCLEAR REACTOR BY DISPLACING IN THE CORE OF THE REACTOR GROUPS OF CONTROL RODS

When the control parameter ( DELTA T) is within its deadband, a correction of the axial deviation of power (DA) is effected by movement of at least one group of control rods, when DA is outside a predetermined range or deadband straddling a reference value DA ref. The group which is moved is chosen as a function of the sign of DELTA T, of the position of DELTA T with respect to its deadband and of the position of the other groups. When DELTA T is outside its deadband, the differences between the amplitudes of insertion of the groups participating in the control of the reactor are made to vary by stopping or starting of groups selected as a function of the positions of the groups of rods (G1, G2, N1, N2) in the core of the reactor and of the position of DA either with respect to its deadband if DA is outside this deadband, or with respect to DA ref, if DA is within this deadband. The invention is in particular applicable to pressurized-water nuclear reactors.