Abstract: A detector assembly for in-core nuclear reactor monitoring in which the wall thickness of the outer housing tube 26a and the wall thickness of the inner calibration tube 28a, taken together with the diameters of operating and non-operating elements 34a, 36a, 38 filling the annular space between the tubes and each having interior highly compacted mineral insulation, provide a total thickness dimension adequate to meet code primary pressure requirements for normal nuclear reactor in-core conditions, with the OD of the outer housing tube permitting passage of the assembly through most existing assembly guide tubes 18, and the ID of the calibration tube being adequate to receive movable detectors 48 of a larger, standard size, thus permitting use of in-place standard drive systems.

Abstract: A neutron detection system is described which is operable over a wide range of neutron flux levels. The system includes a fission type ionization chamber neutron detector, means for gamma and alpha signal compensation, and means for operating the neutron detector in the pulse counting mode for low neutron flux levels, and in the direct current mode for high neutron flux levels.