Patent Number: 
Section: claims

1. A control rod operation monitoring method of monitoring a plurality of control rods inserted into a core,wherein a plurality of neutron detector assemblies, each including a plurality of neutron detectors arranged in an axial direction of the core, are disposed adjacent to each of the control rods, including insertion selection control rods selected from the plurality of control rods for insertion into the core,wherein first neutron detectors, of the plurality of neutron detectors, are respectively arranged at first positions in each said neutron detector assembly and a plurality of second detectors, of the plurality of neutron detectors, are respectively arranged at second positions in each said neutron detector assembly,wherein each said first position in each said neutron detector assembly is closest to a control rod insertion end of the core, andwherein each said second position in each said neutron detector assembly is different in the axial position from the first position, the method comprising:for each one of the plurality of insertion selection control rods, calculating a first average neutron flux of neutron fluxes measured from each of said first neutron detectors in each of said neutron detector assemblies disposed adjacent to the one insertion selection control rod;for each one of the plurality of insertion selection control rods, calculating a second average neutron flux of neutron fluxes measured from each of said second neutron detectors in each of said neutron detector assemblies disposed adjacent to the one insertion selection control rod;for each one of the plurality of insertion selection control rods, calculating a first neutron flux ratio, each said first neutron flux ratio being a ratio of the second average neutron flux with respect to said first average neutron flux; andupon determining the first neutron flux ratio of one of the insertion selection control rods exceeds a predetermined neutron flux ratio, generating a rod insertion block signal for the one insertion selection control rod. 2. The control rod operation monitoring method according to claim 1, comprising: averaging neutron fluxes measured by the neutron detectors located at the first positions of each of all the neutron detector assemblies arranged in the core; averaging neutron fluxes measured by the neutron detector located at the second positions of each of all the neutron detector assemblies; calculating a second neutron flux ratio which is a ratio of an average of the neutron fluxes at the second positions of all the neutron detector assemblies with respect to an average of the neutron fluxes at the first positions of all the neutron detector assemblies; and generating rod insertion block signals for all control rods including the ones of the insertion selection control rods in the core when the second neutron flux ratio exceeds a set neutron flux ratio. 3. The control rod operation monitoring method according to claim 2, wherein all the control rods including the insertion selection ones of the control rods are blocked from being inserted into the core by the rod insertion block signal when the second neutron flux ratio exceeds the set neutron flux ratio. 4. The control rod operation monitoring method according to claim 1, wherein the one insertion selection control rod is blocked from being inserted into the core by the rod insertion block signal. 5. The control rod operation monitoring method according to claim 4, wherein after the one insertion selection control rod is blocked from being inserted into the core, all the control rods are urgently inserted into the core. 6. The control rod operation monitoring method according to claim 1, wherein all the control rods are urgently inserted into the core by the rod insertion block signal.