Patent Number: 06236698&
Section: claims

1. A nuclear reactor instrumentation system, comprising: a plurality of in core nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core,  said in core nuclear instrumentation assemblies each including a fixed type neutron detector assembly and a fixed type gamma thermometer assembly,  wherein said fixed type neutron detector assembly comprises N fixed neutron detectors dispersively arranged in a core axial direction with a predetermined interval L, where N is an integer greater than and equal to four, and  said fixed type gamma thermometer assembly comprises at least 2N-1 fixed type gamma ray heat detectors arranged in the core axial direction such that N of the at least 2N-1 fixed type gamma ray heat detectors are arranged at the same core axial position as the fixed type neutron detectors and a reminder N-1 of the fixed type gamnma ray heat detectors are arranged at an intermediate position in the core axial direction between said fixed type neutron detectors;  a power range detector signal processing device operatively connected to said fixed type neutron detector assemblies through signal cables; and  a gamma thermometer signal processing device operatively connected to said fixed type gamma thermometer assembly of the in core nuclear instrumentation assembly through a signal cable. 2. The system according to claim 1, wherein one of said fixed type gamma ray heat detectors of the fixed type gamma thermometer assembly is arranged at a position L/4 above the lowest fixed type neutron detector. 3. The system according to claim 1, wherein in a case where the effective fuel portion of the reactor core is divided into several nodes in the core axial direction, each of core axial positions of said fixed type neutron detector and the fixed type gamma ray heat detector are coincident with a center of each of the nodes. 4. The system according to claim 1, wherein said fixed type neutron detectors constituting the fixed type neutron detector assembly is arranged so as to be calibrated respectively by said fixed type gamma ray heat detectors located on the same core axial position and each of said fixed type neutron detectors is calibrated so as to be coincident with a converted gamma ray heating value obtained from the gamma ray heat detector located on the same core axial position.