Patent Number: 046648798
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to a guide tube flow restrictor for use in conjunction with drive rod assemblies of a pressurized water nuclear reactor. The guide tube flow restrictor serves both to act as a guide for a drive shaft connected to a control rod and as a flow restrictor for primary coolant passing through the reactor. In pressurized water nuclear reactors, the reactor head plenum contains a guide assembly for controlling the movement of various components such as control rods. Such an assembly generally contains a top support plate, having apertures therethrough, through which drive mechanisms for control rods pass. A guide assembly is provided that is disposed in the apertures to both guide the control rod drive shaft and control the upward flow of water through the apertures. Conventionally, such assemblies comprise a grommet-like member secured in the aperture by a plurality of flexure elements aligned in parallel relationship with he drive shaft, which flexure elements are mounted in special fittings supported in the top plate. Such conventional assemblies require machining and welding operations for installation of the flexure members and require time-consuming procedures for their replacement. An improved type of assembly is described in copending application Ser. No. 574,839 filed Jan. 30, 1984 in the names of David E. Boyle and James R. Chrise, entitled "Quick Release Guide Sleeve Assembly", which application is assigned to the assignee of the present invention, the contents of said application incorporated herein by reference. In said application, the assembly comprises an outer sleeve, an inner sleeve, and a locking mechanism movably mounted on the outer sleeve for frictionally engaging the wall surfaces about an aperture in a top support plate of a guide tube rod assembly. The assembly described therein still, however, requires the use of a tool for assembly, as well as disassembly. Also, the construction is such that corrosion or accumulation of deposits about the locking mechanism could develop that would lead to difficulties in removal and replacement of such an assembly. It is an object of the present invention to provide a guide tube flow restrictor that may be assembled without the need for special tools and is readily removable from its position in a support plate. It is another object of the present invention to provide a guide tube flow restrictor that has a design that simplifies manufacture of such an assembly and is more economical. It is a further object of the present invention to provide a guide tube flow restrictor that reduces the possibility of corrosion or collection of deposits between the assembly parts in use, such as would cause difficulties in removal or replacement of the assembly. SUMMARY OF THE INVENTION A guide tube flow restrictor for use in an upper guide tube support plate comprises an outer ring that is seatable on the support plate, with a bore through the ring aligned with an aperture in the support plate, and an inner sleeve coaxially insertable in the outer ring. The outer ring has a flange member that carries a plurality of downwardly extending flexible segments which extend through the bore and the aperture of the support plate. Upon axial insertion of the inner sleeve into the bore of the outer ring, the sleeve contacts deflecting means on the flexible segments and force the segments radially outwardly to frictionally secure the same with the walls of the aperture of the support plate and lock the assembly in place. The flexible segments preferably terminate in an outwardly disposed leg portion which contacts the bottom of the wall of the aperture in the support plate and also carry an inwardly protruding baffle to deflect the upflow of water away from the bottom of the inner sleeve, while the deflecting means preferably comprises an inwardly protruding extension having at least one angular strut extending upwardly therefrom to the flexible segment, with contact of the inner sleeve confined to the angular surface of the strut. Shoulders are provided on the outer ring to prevent accumulation of deposits and corrosive problems, while additional locking means may be provided to positively secure the outer ring and inner sleeve together when assembled.