Patent ID: 8804893

Claim:
A method of monitoring the operation of a reactor of a nuclear plant, in which the reactor comprises a core having a plurality of fuel assemblies, wherein each fuel assembly includes a plurality of fuel rods, wherein each fuel rod comprises nuclear fuel and a cladding, the nuclear fuel being enclosed by the cladding, the plant also comprising forcing means arranged to force a coolant in a flow through the reactor and the core, conveying means arranged to convey an off-gas stream from the coolant, a core simulator, and sensors (S) at different positions in the core, wherein the method comprises the steps of: operating the reactor during a normal fuel operation cycle at a given total reactor power, during which fission gases are produced in the fuel rods; continuously measuring during the normal fuel operation cycle a radioactivity level in the off-gas stream for sensing a release of fission gases from the fuel rods as a consequence of a fuel leakage due to a defect on the cladding of any of the fuel rods in any of the fuel assemblies; calculating calculated local power levels (LP C ) at different positions in the core by means of the core simulator; regularly establishing based on the calculated local power levels (LP C ) an instantaneous power distribution (PD I ) in the core during the normal fuel operation cycle by means of the core simulator; establishing a power distribution pattern (PD P ) based on the instantaneous power distributions (PD I ) over time during the normal fuel operation cycle by means of the core simulator; sensing sensed local power levels (LP S ) by means of the sensors (S); comparing the sensed local power levels (LP S ) to the calculated local power levels (LP C ); recalculating and correcting the instantaneous power distribution pattern (PD I ) to establish a corrected power distribution pattern (PD P ) if the sensed local power levels (LP S ) and the calculated local power levels (LP C ) do not correspond; combining the sensed release of fission gases and at least one of the established and the corrected power distribution pattern (PD P ); and determining a position of the defect on the cladding of any of the fuel rods by correlating: changes in the sensed release of fission gases and changes in the sensed local power levels (LP S ), differences between the sensed local power levels (LP S ) and the calculated local power levels (LP C ), and changes in the power distribution pattern (PD P ).