Patent Number: 063209241
Section: description

BEST MODE FOR CARRYING OUT THE INVENTION Referring now to FIG. 1, there is illustrated a nuclear fuel bundle assembly, generally designated 10, including a plurality of fuel rods 12 supported between upper tie plate 14 and a lower tie plate 16. Fuel rods 12 pass through a plurality of fuel rod spacers 18 at vertically spaced positions along the fuel bundle. The spacers 18 provide intermediate support to retain the elongated fuel rods 12 in spaced relation relative to one another and to restrain the fuel rods from lateral vibration. With reference to FIG. 1, a 10.times.10 array of fuel rods is illustrated, while FIG. 6 illustrates an 11.times.11 array. It will be appreciated, however, that the invention hereof is applicable to various arrays of fuel rods of different numbers, for example, 8.times.8, 9.times.9, etc. Each fuel rod 18 is formed of an elongated tubular cladding material, with the nuclear fuel and other materials sealed in the tube by end plugs. The lower end plugs register in bores formed in the lower tie plate 16, while the upper end plugs are disposed in cavities in the upper tie plate 14. Additionally, the fuel rod assembly includes a channel 20 of substantially square cross section, sized to form a sliding fit over the upper and lower tie plates and the spacers, so that the nuclear fuel bundle, including the channel 20, tie plates 14, 16, rods 12 and spacers 18 can be removed from the reactor core (not shown). Turning now briefly to FIGS. 6 and 7, there is illustrated a spacer 18 constructed in accordance with the present invention, and having a plurality of individual ferrules 22 and springs 24, each ferrule 22 having a single associated spring 24, which bears against a single fuel rod 12' in a respective ferrule. The ferrules 22 are arranged in a square matrix in which each ferrule receives a fuel rod 12' and maintains the fuel rods spaced and restrained relative to adjoining fuel rods. The spring 24 of each ferrule biases its associated fuel rod in a lateral direction against hard stops 26 opposite the spring, whereby each fuel rod 12' is maintained in a predetermined position relative to one another and within the marginal band 28 of the spacer 18. The marginal band 28 normally includes inwardly directed flow tabs 30, but the latter form no part of this invention. With reference back to FIG. 2, each spacer ferrule 22 has a generally hollow, generally cylindrical configuration. The wall of each cylindrical ferrule is indented at circumferentially spaced locations along one side of the ferrule to form the inwardly directed, axially extending hard stops 26. It will be appreciated that the stops 26 extend the full height of the ferrule, although the stops could be provided at axially spaced locations along the height of the ferrule. As best illustrated in FIG. 2, each ferrule 22 includes a central spring opening 30 opposite the hard stops 26. Spring opening 30 is defined partially by upper and lower circumferential bands 32, 34. Between these two bands, the opening 30 is centrally located and has a substantially "I" shape which includes relatively wider upper and lower portions 36, 38 connected by a narrower axially extending stem portion 40. The opening 30 is more specifically formed by upper and lower horizontal edges 42, 44, upper vertical edges 46, 48 which are connected to the vertical stem edges 50 and 52 by means of horizontal steps or shoulders 54, 56. Similarly, lower vertical edges 58 and 60 are connected to the vertical stem edges 50 and 52 by step or shoulder surfaces 62, 64. As already noted above, the opening 30 is directly opposite and centered relative to the hard stops 26. FIG. 3 illustrates the spring 24 in detail. The spring also has a substantially "I" shape which includes, generally, a planar body including upper and lower horizontal flanges 64, 66, respectively, interconnected by a vertical stem 68. The spring 24 also includes a pair of T-shaped cutouts, one of which is upright and located in the upper half of the spring, while the other is inverted and located in the lower half of the spring. Thus, the upper cutout 70 includes a horizontal portion 74 and a vertical portion 76 whereas the lower cutout 72 includes a horizontal portion 78 and a vertical portion 80. These openings increase the flexibility and resilience of the spring 24 as will be appreciated by those of ordinary skill in the art. The spring 24 is substantially planar except as noted below. In the upper half of the spring, the horizontal band 82 lying adjacent the horizontal portion 74 of the opening 70 is formed to include a radially outward tab or projection 84 in substantially axial or vertical alignment with the vertical portion 76 of the T-shaped cutout 70. A similar radially outwardly extending projection 86 is formed in the lower band 88 lying adjacent the horizontal portion 78 of the T-shaped cutout 72. Both projections 84 and 86 extend outwardly to substantially the same degree. In the center of the stem portion of the spring, between the vertical portions 76, 80 of the T-shaped cutouts 70, 72, respectively, there is formed a radially inwardly directed projection 89 which is further formed to include a radially inwardly extending dimple 90 which is designed to engage a fuel rod in the associated ferrule 22. With further reference now also to FIGS. 4 and 5, the spring 24 may be aligned and seated within the opening 30 such that the projection 88 and dimple 90 extend radially inwardly into the interior space of the ferrule 22, but the upper and lower flanges 64 and 66 remain on the outside of the ferrule 22. The size of the opening 30 is designed so that the spring 24 is relatively snugly received in the opening, with upper and lower edges 92, 94, respectively, supported by upper and lower edges 42, 44. respectively, of the opening 30. At the same time, vertical edges 96, 98 of the projection 88 are supported by the edges 50, 52 of the opening 30. In this way, both vertical and lateral movement of the spring 24 relative to the ferrule opening 30 is substantially precluded. It will also be noted that the movement of the spring 24 toward or away from the fuel rod 100 is limited by the edges 46, 48, 58 and 60 of the opening 30. Limiting the spring's freedom of movement is achievable because both the ferrule opening shape and the spring shape are formed by stamping, which is a reliable manufacturing process for dimensional stability. Typically, when the spacer ferrules 22 are placed within the spacer band prior to welding, the ferrules 22 are aligned as shown in FIG. 6 with all of the hard stops 26 and spring openings 30 similarly aligned. During placement of the ferrules, the springs 24 are located within the respective openings 30 and the ferrules 22 are then welded together at diametrically opposed locations between the hard stops 26 and the opening 30. These welds are shown in FIG. 7 by letter designations W.sub.1 and W.sub.2, with the understanding that all of the ferrules are welded in a similar manner. It will be appreciated that when a fuel rod 12' is inserted within the ferrule 22, the rod 12' contacts the hard stops 26 and the dimple 90. In this regard, FIG. 7 illustrates the fuel rod 12' in phantom while the spring 24 is shown in its relaxed position. In this way, it is to be understood that when the fuel rod is inserted within the ferrule, the dimple 19 and indeed the entire vertical stem of the "I" spring will be flexed radially outwardly to accommodate the rod, with the resulting bias of the fuel rod 12' against the hard stops 26. With all of the springs and ferrules similarly aligned as shown in FIGS. 6 and 7, the bundles can be oriented horizontally for shipment in such a way that any loads which occur during bundle shipment to customers are taken by the hard stops 26 on the ferrules and not by the springs. In addition, the unique "I" shape of the springs 24 in accordance with this invention, results in only a minimal protrusion of material into the subchannel flow. This, in combination with the tight capture of the spring within the ferrule cutout, securely holds the spring against the water induced movement that could otherwise cause wear. 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.