Patent Number: 
Section: claims

1. A method for operating a pressurized water nuclear reactor, said reactor comprising:a core producing power;a plurality of control rod clusters for controlling the reactivity of said core, said plurality of control rod clusters capable of occupying in the core a plurality of insertion positions staged vertically from an uninserted position;operating means for acquiring quantities representative of the operating conditions of the core;said method comprising the steps of:measuring an effective power of the nuclear reactor;acquiring a reference value for a desired target power of the nuclear reactor;acquiring an estimated duration of an amount of time needed for power to increase from said effective power to said reference value for the target power;determining a reference position of at least one control rod cluster among said plurality of control rod clusters, wherein the reference position is needed for acquiring said reference value for said desired target power, wherein the reference position is determined as a function of said estimated duration, of said measured effective power and of said reference value for said target power;acquiring an estimated point of time of the start of said power increase, said estimated point of time corresponding to an end of a stage of said effective power and being taken into account in the step of determining the reference position of at least one control rod cluster; andpositioning said at least one control rod cluster in its reference position at or before said estimated point of time. 2. The method for operating a pressurized water nuclear reactor according to claim 1, further comprising regulating the concentration of a neutron absorbing element in the coolant as a function of said reference position of at least one control rod cluster among said plurality of control rod clusters by operations of dilution and/or boronation of the primary coolant of said nuclear reactor. 3. The method for operating a pressurized water nuclear reactor according to claim 2 wherein the neutron absorbing element is boron. 4. The method for operating a pressurized water nuclear reactor according to claim 1, wherein said step of determining said reference position of said at least one control rod cluster is carried out via software implementing a neutron code. 5. The method for operating a pressurized water nuclear reactor according to claim 1, wherein said step of determining said reference position of said at least one control rod cluster comprises:a sub-step of determining a first position of at least one control rod cluster as a function of said measured effective power and of said reference value for the target power;a sub-step of determining a variation in a concentration of xenon in said core of said reactor during the power increase, said variation in xenon concentration being a function of said estimated duration, and/or of said measured effective power and/or of said reference value for the target power; anda sub-step of determining a corrective factor of the position of at least one control rod cluster as a function of said variation in the xenon concentration. 6. The method for operating a pressurized water nuclear reactor according to claim 1, wherein said step of determining said reference position of said at least one control rod cluster comprises:a sub-step of determining a first position of at least one control rod cluster as a function of said measured effective power and of said reference value for the target power;a sub-step of determining a variation in a xenon concentration in said core of said reactor during the power increase, said variation in the xenon concentration being a function of said estimated duration, and/or of said measured effective power and/or of said reference value for the target power, and/or of said estimated point of time of the start of increase in power; anda sub-step of determining a corrective factor of the position of at least one control rod cluster as a function of said variation in the xenon concentration.