Patent Number: 054426650
Section: claims

1. A method for monitoring flow-induced vibration in a cylindrical housing which extends upwardly through a bottom head of and into an interior of a reactor pressure vessel of a nuclear reactor, comprising the steps of: connecting a vibration sensor to one end of a signal cable; and  attaching said vibration sensor to an inside surface of said cylindrical housing,  whereby said one end of said signal cable lies inside said reactor pressure vessel, another end of said signal cable lies outside said reactor pressure vessel and an intermediate portion of said signal cable penetrates said reactor pressure vessel.  arranging a portion of said signal cable in an annular space between a pair of concentric thin-walled tubes with said vibration sensor outside of said annular space;  spot welding said thin-walled tubes to each other to form an assembly; and  inserting said assembly inside said cylindrical housing.  inserting a mandrel inside an inner one of said thin-walled tubes, said mandrel having a flange for supporting said assembly;  adhering said vibration sensor to a surface of said mandrel; and  sliding said coupled mandrel and assembly inside said cylindrical housing.  a vibration sensor attached to an inside surface of said cylindrical housing; and  a signal cable coupled to said vibration sensor at a location inside said reactor pressure vessel and extending through the reactor pressure vessel and into an exterior of said reactor pressure vessel.  a first tube having a circular cylindrical portion of first diameter connected to a retained portion;  a second tube having a circular cylindrical portion of second diameter connected to a retained portion, said second diameter being less than said first diameter;  means for supporting said circular cylindrical portion of said first tube in a concentric position relative to said circular cylindrical portion of said second tube, said supporting means being connected to an inner surface of said circular cylindrical portion of said first tube and to an outer surface of said circular cylindrical portion of said second tube;  a signal cable having a first portion which is routed through a space between said circular cylindrical portions of said first and second tubes and having second and third portions which are not routed in said space, said second and third portions being connected to opposite ends of said first portion;  a generally annular body comprising a central bore for receiving said retained portions of said first and second tubes and a penetration bore for receiving said second portion of said signal cable;  means for attaching said retained portions of said first and second tubes to said generally annular body; and  an instrument connected to said third portion of said signal cable. 2. The method as defined in claim 1, wherein said cylindrical housing has a circular cross section, and the following steps are performed prior to said step of attaching said vibration sensor to said inside surface of said cylindrical housing: 3. The method as defined in claim 1, wherein said cylindrical housing is an in-core monitor housing. 4. The method as defined in claim 1, wherein said vibration sensor comprises a strain gage. 5. The method as defined in claim 1, wherein said step of inserting said assembly inside said cylindrical housing comprises the steps of: 6. The method as defined in claim 5, further comprising the step of removing said mandrel from said assembly before said step of attaching said vibration sensor to said inside surface of said cylindrical housing. 7. An apparatus for monitoring flow-induced vibration of a cylindrical housing which extends upwardly through a bottom head of and into an interior of a reactor pressure vessel of a nuclear reactor, comprising: 8. The apparatus as defined in claim 7, further comprising means for protecting a first portion of said signal cable located inside said cylindrical housing, and penetration means for passing a second portion of said signal cable through a pressure boundary between said interior and said exterior of said vessel. 9. The apparatus as defined in claim 8, wherein said protecting means comprises an outer thin-walled tube and an inner thin-walled tube, said inner tube being arranged concentrically inside said outer tube to form an annular space therebetween, said first portion of said signal cable residing in said annular space. 10. The apparatus as defined in claim 9, wherein said first portion of said signal cable is helically wound around said inner tube. 11. The apparatus as defined in claim 9, wherein said inner and outer tubes are spot-welded together. 12. The apparatus as defined in claim 9, wherein said inner and outer tubes each have a wall thickness on the order of 4 mils. 13. The apparatus as defined in claim 9, wherein said penetration means comprises a bore formed in a flange insert and a hole formed in said outer tube, said flange insert being adapted to be sandwiched between a pair of flanges, one of said pair of flanges being integrally joined to said cylindrical housing, and further comprising means for attaching said inner and outer tubes to said flange insert so that said bore is in communication with said annular space. 14. The apparatus as defined in claim 13, further comprising means for sealing a space between said bore and said second portion of said signal cable to form said pressure boundary. 15. The apparatus as defined in claim 14, wherein said sealing means comprises fused braze or weld material. 16. The apparatus as defined in claim 9, wherein said attaching means comprises a snap ring with buttwelded ends which seats in an annular groove formed in an inner circumferential surface of said flange insert. 17. An instrumentation assembly comprising: 18. The instrumentation assembly as defined in claim 17, wherein said instrument is a vibration sensor. 19. The instrumentation assembly as defined in claim 17, wherein said supporting means comprises a multiplicity of spot welds. 20. The instrumentation assembly as defined in claim 17, wherein said first-and second tubes each have a wall thickness on the order of 4 mils. 21. The instrumentation assembly as defined in claim 17, wherein said attaching means comprises a snap ring with butt-welded ends which seats in an annular groove formed in said central bore of said generally annular body, said retained portions of said first and second tubes being arranged between said snap ring and said annular groove. 22. The instrumentation assembly as defined in claim 17, wherein said circular cylindrical portion of said first tube has a penetration hole formed therein which is in communication with penetration bore, said signal cable extending from said annular space into said penetration bore via said penetration hole.