Abstract: A nuclear reactor internal pump has a pump shaft connected to a motor and rotatably passing through the bottom of a nuclear reactor pressure vessel, an impeller fitted to a front end portion of the pump shaft, a diffuser disposed on the downstream side of the impeller and having an inner cylinder fixed to the bottom of the reactor pressure vessel to surround the pump shaft, a purge water passage defined between the pump shaft and the inner cylinder to communicate with the inside of the reactor pressure vessel and a purge water supply device for supplying purge water to reactor pressure vessel through the passage. Further, the nuclear reactor internal pump comprises a clad dropping preventive device for trapping clad coming from the reactor pressure vessel in the passage to prevent the clad from dropping.

Abstract: The recirculating flow rate of the primary coolant recirculated a nuclear reactor pressure vessel by an internal pump disposed therein is measured by a device which comprises a flow passage resisting device located in the recirculating flow passage of the primary coolant for creating between the upstream and downstream sides thereof a pressure difference in the primary coolant flow and detectors disposed at the upstream and downstream sides of the flow passage resisting device to detect the pressure difference therebetween. The thus detected pressure difference is converted into a corresponding electric signal by a transmitter which then transmits the signal to a device for computing the recirculating flow rate of the primary coolant in response to the signal. The device may further comprise an auxiliary measuring device for measuring a core flow rate of the primary coolant in a manner similar to that in the pumping flow rate measurement described above.