JP2645188B

PURPOSE:To obtain monitor information including a state of a detecting unit by detecting presence or absence of a power source by a plurality of detecting means mounted at an electric circuit of a drive motor for driving a recirculation pump and using it as a stop signal of the pump through a logic circuit. CONSTITUTION:When a voltage between two phases connected with a transformer 15 for an instrument, is lowered to a set value or less, insufficient voltage signals S17a, S17b are generated, and output from first OR circuits 20a, 20b. In this case, AND operations of them are performed together with selective control rod region signals S25a, S25b to be output from a nuclear measuring board 25 by first AND circuits 21a, 21b, and output to a second OR circuit 22a. Thus, an output of the circuit 22a is input to one input terminal of a second AND circuit 23. Further, a mutual confirmation with a voltage signal of a different phase by the same power source, is performed, and stop of a recirculation pump 1 is judged from confirmation of presence or absence of power to be applied to a drive motor 2. Thus, the stop of the pump can be detected.