CONTROLLING METHOD FOR BOILING WATER REACTOR POWER PLANT

PURPOSE:To avoid nuclear reactor scram and stably supply power by simultaneously tripping a plurality of internal pumps and stopping core flow drop scram signal at the time when core flow rate drops more than a specified value. CONSTITUTION:If generator load cutoff is generated, a steam control driver 211 quickly shuts off a steam control valve 21 and sends a steam control valve quick shut-off signal 8. The signal 8 quickly opens a turbine bypass valve 21, terminates a half, for example, of internal pumps 2-1 to 2-10 and inserts controller 29 properly. By the way, if a half of the pumps 2-1 to 2-10 terminates, core flow drop results in core flow quick scram and a core flow drop judgment circuit 700 outputs core flow drop scram signal 708. If the signal 8 and the signal 708 are input simultaneously, a core flow scram circuit 200 stop the signal 708 from being output to a reactor scram logic 7 and the generation of reactor scram is avoided.