Patent Number: 043158005
Section: claims

1. In a nuclear reactor comprising a reactor core, a shroud enclosing said reactor core, a pressure vessel surrounding said shroud and defining a vertical annular space between the vessel and the shroud, and a plurality of internal circulation pumps disposed in a lower portion of said vertical annular space for forcing a coolant in said vertical annular space to flow into below said reactor core so that the coolant flows through the reactor core in forced circulation, the improvement comprising means for vertically guiding over a predetermined distance a flow of the coolant being sucked into each said internal circulation pump to increase the effective inertia of the flow of the coolant, to thereby enhance the stability of the flow conditions of the coolant flowing through the reactor core, said guide means including a tubular guide member in the form of a venturi tube for each said internal circulation pump, and further comprising flow measurement means associated with said venturi tube for measuring the flow rate of the coolant flowing through said reactor core. 2. A nuclear reactor as claimed in claim 1, wherein said predetermined distance is about 2-10 times the diameter of a suction port of each said internal circulation pump when the length of a fluid guide of said pump is added thereto. 3. A nuclear reactor as claimed in claim 1, wherein said tubular guide member in disposed adjacent a suction port of each said internal circulation pump and extending substantially coaxially therewith in a vertical direction. 4. A nuclear reactor as claimed in claim 3, wherein said tubular guide member has at its upper and lower ends an inner diameter which is substantially equal to the diameter of an inlet of a casing of the internal circulation pump, and said tubular guide member is securedly connected at its lower end to an upper end of the casing. 5. A nuclear reactor as claimed in claim 3 or 4, wherein said tubular guide member has a length which is about 2-10 times the diameter of the suction port of the pump or the inlet of the casing when the length of the fluid guide of the pump is added thereto. 6. A device for forcing a coolant to circulate through a nuclear core within a nuclear reactor in which a vertical annular space is defined between a shroud enclosing the reactor core and a pressure vessel surrounding said shroud so that a coolant circulates within the nuclear reactor by flowing from said vertical annular space into below the core and then flowing through the core, said device comprising a plurality of internal circulation pumps located in a lower portion of said vertical annular space for forcing the coolant in said vertical annular space to flow into below said reactor core so that the coolant flows through the reactor core in forced circulation, and tubular guide members each disposed adjacent a suction port of each said internal circulation pump for vertically guiding a flow of the coolant being sucked into the internal circulation pump to thereby increase the effective inertia of the coolant flow, each said tubular guide member being a venturi tube, and further comprising flow measurement means associated with said venturi tube for measuring the flow rate of the coolant flowing through the reactor core. 7. A device as claimed in claim 6, wherein each said tubular guide member has a length which is about 2-10 times the diameter of a suction port of each said internal circulation pump when the length of a fluid guide of said pump is added thereto. 8. A device as claimed in claim 6 or 7, wherein each said tubular guide member has at its upper and lower ends an inner diameter which is substantially equal to the diameter of an inlet of a casing of said internal circulation pump, and said tubular guide member is securedly connected at its lower end to an upper end of the casing. 9. A device as claimed in claim 1, wherein said measurement means includes means for measuring the coolant delivery of each said internal circulation pump in accordance with a differential pressure of the associated venturi tube. 10. A device as claimed in claim 6, wherein said measurement means includes means for measuring the coolant delivery of each said internal circulation pump in accordance with a differential pressure of the associated venturi tube.