Local power region monitor in a boiling water reactor

Object: To use a local power region monitor (LPRM) to readily detect abnormal oscillation of string, while maintaining a function of a traversing incor probe (TIP). Structure: At the lower end of a TIP guide tube within a string is mounted a guide tube change-over device, to which are connected one or more TIP inserting guide tubes and one or more oscillator-meter inserting guide tubes. An oscillator-meter is disposed within the oscillator-meter inserting guide tube, said oscillator-meter is connected to an oscillation recording device by a signal transmission line. In this manner, the oscillator-meter is guided to the TIP guide tube within the core so that it may be travelled within the TIP guide tube or stayed therein to detect oscillation of LPRM string resulting from a flow of cooling water. (Kamimura, M.)