Patent Number: 
Section: claims

1. A structure for suppressing flow induced vibration in a nuclear reactor vessel comprising:a guide tube provided inside a hollow upper core support column interposed between an upper core support plate and an upper core plate in a reactor vessel;a head nozzle provided at a lower end of the upper core support column; andan instrumentation tube disposed inside the guide tube, whereina lower hole is provided at a lower portion of a side surface of the guide tube, andthe instrumentation tube is disposed to contact with an inner circumferential surface of the side surface of the guide tube on which the lower hole is provided, such that the instrumentation tube is pressed against the side surface by a differential pressure between coolant inside and outside the lower hole. 2. The structure for suppressing flow induced vibration according to claim 1, whereina pressure adjustment hole is provided at a side surface of the upper core support columnfor allowing coolant flowing into the guide tube from a lower end of the guide tube to flow out to outside from inside the guide tube through a gap between the instrumentation tube and the lower hole, and then to flow out to outside from inside the upper core support column through the pressure adjustment hole. 3. A structure for suppressing flow induced vibration in a nuclear reactor vessel comprising:a guide tube provided inside a hollow upper core support column interposed between an upper core support plate and an upper core plate in a reactor vessel;a head nozzle provided at a lower end of the upper core support column; andan instrumentation tube disposed inside the guide tube, whereinan upper hole and a lower hole are provided at two portions, namely an upper portion and a lower portion, of a side surface of the guide tube, andthe instrumentation tube is disposed to contact with an inner circumferential surface of the side surface of the guide tube on which the upper hole and the lower hole are provided, such that the instrumentation tube is pressed against the side surface by a differential pressure between coolant inside and outside the upper hole and the lower hole. 4. The structure for suppressing flow induced vibration according to claim 3, whereinan upper pressure adjustment hole and a lower pressure adjustment hole are provided at two positions, namely, an upper portion and a lower portion, of a side surface of the upper core support columnfor allowing the coolant flowing into the guide tube from an upper end of the guide tube to flow out to outside from inside the guide tube through a gap between the instrumentation tube and the upper hole, and also to flow out to outside from inside the upper core support column through the upper pressure adjustment hole, andfor allowing coolant flowing into the guide tube from a lower end of the guide tube to flow out to outside from the inside of the guide tube through a gap between the instrumentation tube and the lower hole, and also to flow out to outside from inside the upper core support column through the lower pressure adjustment hole. 5. The structure for suppressing flow induced vibration according to claim 3, whereinthe upper hole and the lower hole are formed in slits extending in an axis direction of the guide tube, and includes expanded portions expanded in oval shapes at middle portions of the slits.