Thimble guide extender for a nuclear power plant

Abstract

A sleeve-like sealing unit, particularly a thimble guide extender is adapted to be installed on and coaxially with a thimble guide mounted on a lower core plate of a nuclear reaction vessel and projects toward and terminates at a distance from an underface of a bottom nozzle forming part of a fuel assembly and supported on a top face of the lower core plate. The extender has a lower fitting adapted to surround the thimble guide at a bottom length portion thereof adjacent the top face of the lower core plate; and an upper fitting being axially displaceable relative to the lower fitting and being adapted to surround the thimble guide at a top length portion thereof. The upper fitting has an axial passage and a terminal opening defined by an outer annular radial face adapted to be in a face-to-face engagement with the underside of the bottom nozzle. The extender further has an axially compressible, generally cylindrical resilient bellows arranged between the lower and upper fittings generally in axial alignment therewith and being sealingly secured thereto. In an installed state of the extender the belows is compressed and urges the annular radial face of the upper fitting into a sealing contact with underside of the bottom nozzle. A circumferential sealing arrangement is provided at the lower fitting and is adapted to sealingly surround the thimble guide in the installed state of the extender.