In a nuclear reactor wherein a plurality of neutron detectors are arranged vertically and at equal azimuth angles around a core of the nuclear reactor, thereby to measure a vertical power profile with a core of the reactor core, the improvement comprising dividing the core into sectors at respective azimuth angles confronting the neutron detectors, usingg the output signal of the partial detectors included in each of the neutron detectors for measuring a vertical reactor power profile of the azimuthal sector of the core confronting the corresponding neutron detector, and averaging the vertical profiles of the respective azimuthal parts with respect to the azimuth angles to measure the vertical reactor power profile of the reactor.
This application is a continuation of application Ser. No. 07/595,745, filed on Oct. 10, 1990, which is a continuation of prior application Ser. No. 07/355,808, filed on May 22, 1989 which is a continuation of prior application Ser. No. 07/000,765, filed on Jan. 6, 1987, all now abandoned.
