Fuel spacer/water rod capture apparatus and methods for boiling water nuclear reactors

#The present invention relates to apparatus and methods for axially and non-rotationally fixing one or more spacers and a water rod to one another in a nuclear fuel bundle assembly and particularly relates to spacer/water rod capture apparatus and methods for assembly and disassembly of the water rods and spacers.

#In boiling water nuclear reactors, fuel rods are grouped together in an essentially open-ended tubular flow channel, typically referred to as a fuel assembly or bundle. A plurality of fuel assemblies are positioned in the reactor core in a matrix and a coolant/moderator flows upwardly about the fuel rods for generating steam. The fuel rods are supported in each assembly between upper and lower tie plates. One or more water rods are usually located interiorly within each fuel rod bundle. Spacers are employed at predetermined elevations along each fuel bundle to restrain the fuel rods from bowing or vibrating during reactor operation.

#Typical spacers often include a plurality of ferrules arranged in side-by-side relation and secured, for example, by welding to one another to form a support matrix for the fuel rods. Generally, the role of the spacer in a fuel bundle assembly is to maintain the rods in fixed lateral locations relative to one another. These spacers are secured or captured in a manner preventing their movement relative to the longitudinal axis of the bundle during operation of the reactor. Conventional methods of maintaining the fuel rod spacers in position along the axis of the bundle include the use of a pair of tabs welded to the water rods engaging a spacer along its top and bottom, preventing axial movement of the spacer relative to the water rod in either axial direction. These spacers are assembled onto the water rod by relatively rotating the spacers and water rod such that the tabs pass through an opening in the spacer structure. The spacer is then rotated to an orientation such that part of the spacer structure is axially contacting one of the two tabs, the lower tab being preferred. In the assembled bundle, the water rod is typically prevented from rotation by a square lower end plug received in a square hole in the lower tie plate.

#FIG. 1 is a fragmentary plan view of a portion of a spacer and a water rod illustrating a pair of axially spaced tabs on the water rod for capturing the spacer and water rod together in accordance with the prior art;

#FIG. 2A is a schematic illustration of the orientation of a water rod and spacer clip showing the position of the water rod tab before assembly;

#FIG. 2B is an enlarged fragmentary cross-sectional view illustrating the clip and water rod tab prior to their assembly;

#Referring now to the drawings, particularly to FIG. 1, there is illustrated a spacer for use in a fuel bundle or assembly in a nuclear reactor, the spacer being generally designated 10. The spacer includes a plurality of cylindrical ferrules 12 having stops 13 projecting from interior wall surfaces thereof and springs 16 for bearing against fuel rods 18 extending through the spacer in each of the ferrules 12. The springs 16 impart a lateral force to the fuel rods to maintain the fuel rods in bearing engagement against the stops 13. The spacer 10 also has a surrounding band 20 laterally encompassing the ferrules.

#As illustrated, a pair of water rods 22 pass through enlarged openings in the spacer 10. A clip 24 is secured to the ferrules, for example, by welding, and has a vertical extent corresponding to the vertical extent of the ferrules. One of the water rods 22 carries upper and lower tabs 26 which engage upper and lower margins, respectively, of the clip 24 to prevent relative axial displacement of the spacer and one water rod. As previously stated, in unchanneled bundles, the twist of the water rods and spacers may be sufficient to misalign the tabs 26 with the clip, enabling the spacer and water rod for relative axial displacement.

#Referring to FIGS. 2A-2C, there is illustrated in a preferred form of the present invention, a spacer/water rod connecting structure or retention assembly, generally designated 30, for use in a spacer of the type illustrated in FIG. 1 but having a different clip and water rod retention tab arrangement, as will now be explained. As best illustrated in FIG. 2C, the clip 32 is generally U-shaped with laterally outwardly directed flanges 34 to facilitate welding to adjoining ferrules 12 (FIG. 1). The base of the U-shaped clip 32 defines a slot or opening 36 bounded by axially opposite structural portions 38 and 40, as well as lateral or side structural portions 42 and 44 (FIG. 2B). Thus, the portions 38, 40, 42 and 44 perimetrically enclose the slot 36.