METHOD FOR MONITORING SUBCRITICALNESS OF NUCLEAR REACTOR

摘要

PURPOSE:To exactly detect the subcriticalness of the reactor regardless of the presence or absence of an artificial neutron source and to assure the critical safety by determining the ratio of the neutron count rates before and after a reactivity change operation is made with plural neutron detectors. CONSTITUTION:The ratios between the neutron count rate before the reactivity change operation is made and the neutron count rates after the reactivity change operation is made are determined with the neutron detectors provided in plural detecting positions at the time of monitoring the subcriticalness of the reactor at the reactivity change operation to generate the reactivity change in the reactor under shutdown. The subcriticalness of the reactor is then monitored by the ratios of the neutron count rates and the fluctuation state of the neutron count rates between the respective neutron detectors. The signals of the neutron detectors are used and the characteristics that the change in the signals depends on the change in the neutron multiplication factor of the reactor core are utilized and, therefore, the subcriticalness is monitored with the high accuracy simply by disposing the neutron detectors for plural neutron regions in the reactor core or on the outer periphery thereof in such a manner regardless of the presence or absence of the artificial neutron source.