Reactor failure detection method and device therefor, as well as reactor power control method and device therefor

The present invention concerns detection for failure of a BWR type nuclear power plant and, especially, it provides a device for detecting failures of valves disposed in a main steam system and a reactor power control device to be used upon detection of failure. That is, steams generated in the reactor pressure vessel are introduced to a steam turbine by a plurality of main steam pipelines. Flow rate detectors are disposed to the plurality of main steam pipelines respectively. Occurrence of imbalance in the detected flow rate is measured. When there is found imbalance as the result of the measurement, it is judged that a failure is caused in a main steam isolation valve, a main steam control valve or a main steam stopping valve disposed to the main steam pipelines. The recycling flow rate and a selected control rod driving device are controlled based on the judgement, to lower the reactor power. With such procedures, an accidental event leading to the lowering of the power and stopping for the operation of the reactor can be avoided upon failure of the pressure control device or the valve of the main steam system. (I.S.)