Reactor power monitor

When an average power region monitor (APRM) is calculated from local power monitors (LPRM), the APRM is calculated by two different kinds of calculation methods based on a digitalized LPRM signal in addition to an APRM signal prepared by putting analog signals to AD conversion and averaging thereof. First, the digitalized LPRM signal is subjected passed through to a low-pass filter to eliminate high frequency noises and a dispersion is obtained for each of the signals. It is updated for every predetermined short period of time and past hysteresis is stored in a first and a second memory for a predetermined period of time. The dispersion value is used for judging the importance of the signal and for judging the failure of the monitor. A signal with a large dispersion value in average is determined, for the dispersion value, as a standard signal, a correlation function between a signal and other signal is calculated and it is updated for every short period of time as the same manner as for the dispersion. Accordingly, fluctuations of the nuclear reactor power can be monitored accurately and safety and operation efficiency can be improved. (N.H.)