Nuclear reactor monitoring device

Purpose: To monitor the incore neutron fluxes and the incore thermal behaviors and maintain the soundness of fuel cladding tubes in BWR type reactors. Constitution: A plurality of fuel assemblies are charged to constitute a reactor core in a reactor pressure vessel and detectors are disposed at several positions in the reactor core for detecting the neutron fluxes at each position. The detectors output neutron flux signals, which are sent to a process computer and a transient phenomenon recording device disposed out of the pressure vessel. Then, if fuel assemblies whose minimum critical power ratio exceed an allowable power ratio limit is observed, an alarming device is actuated and the relevant fuel assemblies are displayed on an alarmed fuel assembly display device. Furthermore, if the fuel assembly whose duration time for the alarm power ratio limit exceeds an allowable duration time is observed, the relevant fuel assembly is displayed on a highest alarming fuel assembly display device. (Seki, T.)