Patent Number: 056687281
Section: description

BEST MODE FOR CARRYING OUT THE INVENTION Referring now to the drawing figures, particularly to FIG. 1, there is illustrated a fuel bundle, generally designated B, including a plurality of full-length fuel rods 20 and part-length fuel rods 22. Full-length fuel rods 20 extend the full distance between a lower tie plate 14 and an upper tie plate 16. It will be appreciated that the part-length fuel rods 22 extend from the lower tie plate 14, terminating in the fuel bundle B short of the upper tie plate 16. A plurality of spacers are provided along the length of the fuel bundle, spacers S4 and S5 being illustrated. A channel C also surrounds the matrix of full and partial length fuel rods, as well as the spacers, for confining the liquid flow through the fuel bundle. It will be appreciated that the part-length fuel rods terminate shod of the upper tie plate to define one or more steam vent volumes between the part-length fuel rods and the upper tie plate. For example, four groups of part-length fuel rods 22 of four rods each are illustrated in FIG. 1 defining four steam vent volumes designated as V1-V4. While a 10.times.10 array of fuel rods is illustrated in FIG. 1, it will be appreciated that other arrays of fuel rods may be employed with the present invention, for example, a 9.times.9 array and that other combinations of part-length and full-length fuel rods at various locations within the fuel bundle can be provided. Additionally, deflectors D are illustrated in FIG. 1 at lateral and axial locations within the fuel bundle and above the groups of part-length fuel rods, respectively. It will be appreciated, however, that a single deflector D or string of deflectors can be used in the fuel bundle, for example, at a centrally located position as illustrated in the embodiment of FIGS. 3 and 4 where the part-length rods are disposed only in the central portion of the bundle. As illustrated in FIGS. 1 and 2, the part-length fuel rods may lie in groups of four such rods with deflectors D disposed above the upper ends of those groups of rods, respectively. As illustrated in FIGS. 3-5, the part-length fuel rods 20 may be centrally disposed within the fuel bundle, for example, in a 4.times.4 array, with surrounding fuel rods being symmetrically disposed about the part-length rods 20. Each steam vent region V above a group of part-length rods is thus void of nuclear material and forms a volume for venting steam upwardly within the bundle for flow out of the bundle, e.g., for driving a turbine to generate electricity. It will be appreciated that improved critical power is obtained by maintaining high-density liquid in the interstices of the full-length fuel rods, particularly in the upper two-phase region of the nuclear fuel bundle including the region above the upper ends of the part-length rods. Thus, it is desirable to deflect liquid flowing upwardly within the fuel bundle into the interstices of the full-length rods, while simultaneously providing a path for steam to vent from the fuel bundle. To accomplish this in a fuel bundle employing part-length fuel rods, deflector D is disposed over the upper ends of the part-length rods 22 as illustrated in FIGS. 1-5. As will be seen in FIGS. 3 and 5, the part-length rods are supported in a spacer, for example, spacer S5, and terminate slightly above the spacer. The deflector D may be disposed just above and at distributed locations above the ends of the part-length rods 22 for deflecting liquid passing upwardly within the interstices of the part-length fuel rods 22 laterally outwardly into the interstices of the full-length fuel rods. By deflecting the liquid laterally, the liquid has a tendency to stay within the interstitial volumes of the full-length fuel rods, while the lower density steam may flow therefrom into the steam vent region V above deflector D for flow upwardly and out of the fuel bundle. To locate the deflector D in the fuel bundle, clips 24 are provided on the spacer S5 to maintain the deflector D in position to deflect the liquid laterally outwardly. The deflector D can be removed from the clips and the bundle, providing full access to the part-length rods 22. While the deflector can be releasably supported solely from a spacer, a structural support rod 32 provides support for the deflector 30 from the upper tie plate 16. In this manner, the deflector may be withdrawn through a correspondingly shaped opening in the upper tie plate to provide access to the part-length fuel rods. The deflector 30 may also be releasably supported by a combination of support rod 32 and clips releasably securing the deflector to the spacer. In FIGS. 1 and 2, the deflectors D may comprise flat plates P1-P4 disposed over the upper ends of the groups of part-length fuel rods 22. The deflector plates P1-P4 likewise deflect fluid issuing from the interstices of the part-length fuel rods laterally outwardly into the interstices of the full-length fuel rods. Referring now to FIGS. 6 and 7, the deflector D may be configured other than as a flat plate, particularly to minimize the pressure drop and to improve liquid deflection effectiveness. For example, i FIGS. 6 and 7, a generally inverted pyramidal-shaped deflector 30 is disposed in the steam vent volume V above the upper ends of the part-length fuel rods 22. It will be appreciated that the steam vent volume V defined within the confines of surrounding full-length rods is essentially four-sided and, consequently, the pyramidal-shaped deflector 30 may be inverted and disposed within that rectilinear volume. In FIGS. 8 and 9, a similar inverted pyramidal-shaped deflector 34 is provided. However, the deflector 34 is rotated about a vertical axis about 45.degree. (as compared with the deflector of FIG. 6 and 7) so that the flat triangular sides lie in opposition to the corners of the is rectilinear-shaped steam vent volume V. Thus, the generally triangular-shaped surfaces of deflector 34 are extended upwardly from their bases to fill in the corner areas of the steam vent volume V whereby the horizontally-projected area of the deflector 34 is substantially coextensive with the horizontal rectilinear area of the steam vent path. Liquid flowing upwardly from the interstices of part-length rods 22 is thereby deflected by the flat sides of the inverted deflector 34 into the volumes between the full-length fuel rods 20 to maintain a high density of liquid in that region. Again, the deflector 34 may be supported by a rod 36 depending from the upper tie plate, the deflector being centered with a spacer S, e.g., by clips or springs for easy removal through the upper tie plate. In FIGS. 10 and 11, there is illustrated a generally inverted conical deflector 40 supported by a structural support rod 42 from the upper tie plate and centered by the spacer similarly as in the preceding embodiment. It will be appreciated that because the steam vent volume is generally square in cross-sectional configuration, the conical deflector 40 extends upwardly into the corners of the steam vent volume as illustrated. That is, the conical-shaped surface of deflector 40 is extended upwardly from its full circular base (corresponding in diameter to the width of the steam vent volume) to fill in the corner areas of the steam vent volume V whereby the horizontally projected area of the deflector 40 is substantially coextensive with the rectilinear area of the steam vent path. This inverted conical deflector affords a substantial uniform distribution of liquid into the interstices of the full-length rods. As illustrated in FIGS. 12-14, an eight-sided pyramidal-shaped deflector 50 is provided. In this configuration, four of the flat areas 54 of the eight-sided pyramidal-shaped deflector can be disposed in opposition to the four corners, respectively, of the steam vent volume and extended upwardly beyond the base of the pyramid such that the entire cross-sectional area of the steam vent volume is occupied by portions of deflector 50. Thus, the horizontally projected area provided by deflector 50 is substantially coextensive with the horizontal rectilinear area of the steam vent path. Referring to FIG. 15, an inverted pyramidal or conical deflector 60 is provided with openings in registration with the part-length fuel rods. In this form, the inverted pyramid deflector is disposed at a location lower than the upper ends of the part-length fuel rods by receiving the part-length fuel rods through the respective registering openings. Consequently, the upwardly flowing liquid is deflected outwardly of the interstices of the part-length fuel rods and into the interstices of the full-length fuel rods prior to reaching the level of the upper ends of the part-length rods. Referring to FIG. 16, a cover or lid 70 may be disposed over the deflector plate 60 illustrated in FIG. 15. The cover is in a symmetrical form relative to the inverted deflector. For example, it may comprise an upstanding pyramid corresponding in shape to the inverted pyramidal deflector 60, thereby assisting in reducing the pressure drop across the deflector. Referring to FIG. 17, a swirl deflector is provided. In this configuration, swirl segments 70 are positioned just above one or more of the spacers and overlay the part-length fuel rods 22. A support rod 74 is also provided to mount and remove the swirl deflectors through the upper end of the fuel bundle. In all forms of deflector, the deflector is removable from the bundle or otherwise releasable to a position enabling access to and removal of the part-length rods from the bundle. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.