Results of a flow induced vibration test for a tube in an annulus

In typical PWR plants, neutron flux distribution of the core is monitored during operation by scanning the movable detectors (M/Ds). The M/Ds are driven from about 40 meters away from the core and guided by ICIS (In Core Instrumentation System) thimbles having approximately 40 m length and 8 mm O.D. The ICIS thimbles are inserted into the Fuel Assembly (F/A) thimble tubes through conduit tubes, BMI (Bottom Mounted Instrumentation) nozzles of the Reactor Vessel, BMI columns of Core Internals and so on. This report describes the results of the flow induced vibration experiment on the ICIS thimbles at the similar geometrical conditions and ambient environmental conditions. (J.P.N.)