Patent Number: 050323512
Section: description

Referring to FIG. 1, a fuel bundle B is illustrated. The fuel bundles includes an upper tie plate 42, a lower tie plate 40, which lower tie plate 40 connects through a nose piece N to a boiling water nuclear reactor. In this exemplary construction, individual fuel rods L interconnect the respective tie plates through certain threaded fuel rods also known as tie rods. A channel 25 is mounted about the group of fuel rods. Channel 25 functions to confine fluid flow from nose piece N in through the respective lower tie plate 40 and out through upper tie plate 42. During the operation of a nuclear reactor steam is generated in the fuel bundle assembly. In the particular fuel rod here shown, certain partial length fuel rods 30 are shown. It is to be understood that the spacer design here can be utilized both with full length and partial length fuel rods. As can be seen, the fuel bundle here shown has been broken away at the channel to expose the spacers S1 and S2. The reader will understand that approximately five to eight such spacers are used in the typical fuel rod construction. As has been made clear, the prior art contains many varieties of spacer. An improvement on the so-called "cross point" spacer is the subject of this invention. A typical prior art cross point spacer is illustrated in FIG. 2. Referring to FIG. 2, a prior art cross point spacer construction is shown for a 9.times.9 fuel array. The reader will understand that fuel arrays of varying densities of rods can be covered by the spacer construction of this invention including 8.times.8, 9.times.9 and 10.times.10 fuel rod arrays. Referring to the fuel rod array illustrated in FIG. 2, a series of tube members C' are shown connected by full depth first grid members 51 and second grid members 52. Grid members 51 are orthogonally aligned with respect to grid members 52. Typically fabrication is by welding the respective members 51, 52 to the outside of the respective tube members C'. Surrounding the entire construction there is provided a band D which band D encircles the periphery of the spacer. A portion of the spacer is broken away to illustrate the spacer construction. It is a purpose of this invention to disclose a simplified spacer construction over the construction of FIG. 2. Moreover, a simplified method of spacer construction is set forth. Referring to FIG. 3, a tube member C is illustrated. Tube member C includes transverse notches 60 and longitudinal notches 61. These respective notches 60, 61 have a depth for the full reception of overlying grid members. In exploded relation overlying the tube member C, there is illustrated the construction of the grid members. A transverse member 62 is illustrated with an upwardly exposed notch 64. Similarly, a longitudinal member 63 is illustrated with a downwardly exposed notch 65. Construction is apparent from the exploded view. Specifically, transverse member 62 is confronted to longitudinal member 63 at the confronting notches 64, 65. A grid of the desired dimension is formed such as that grid G illustrated in FIG. 4. Two grids are formed. An upper grid G1 and a lower grid G2. These upper and lower grids fasten to the upper and lower portions of the spacer. Tube member C is notched with respective transverse and longitudinal grooves 60, 61 at the top. Similar transverse and longitudinal grooves 60, 61 are notched at the bottom. It is into these respective notches that the identical top and bottom grids G1 and G2 are placed. At the end of such placement, a semirigid construction of tube members C and grids G1, G2 is formed as shown in FIG. 4 (only grid G1 there being shown in the partial plan view). After assembly, welds are made at locations 5 (FIG. 4) where the grid members fit into notches in the tubes. It will be observed that the spacer at this stage forms a semi-rigid structure. The transverse and longitudinal grid members are interlocked by fitting into the respective notches. This interlocking feature holds the grid members in the correct positions. The grids in turn interlock with the tube members and hold them in their correct position. In contrast to the prior art construction, no jig is required to position the spacer parts for welding. Thereafter, the surrounding band segments N1, N2 are fastened as by welding to the grids, the particular band construction here shown including two band halves joined at 71, 72 typically by a butt weld. Referring to FIG. 5, the completed spacer is illustrated in perspective. As a final step, a drill bit D is shown removing excess material from the final tube member Cx. It will be understood that all excess material has been similarly removed from similar tube members. Viewing the completed spacer it can be seen that a unitary structure having a minimum amount of material has been constructed. Specifically, an upper grid G1 and a lower grid G2 are all interconnected by the tube members C. At the same time, the butt welded and surrounding band N forms an integral spacer structure having a minimum of parasitic neutron absorbing material. Referring to FIG. 6, there is shown in plan view a spacer construction identical to that shown in FIG. 5. In this spacer construction a variable pitch is shown between contained fuel rods L. Specifically, the fuel rods of FIG. 6 are arrayed in a 9.times.9 array. This 9.times.9 array includes eight groups of nine fuel rods each. The groups are designated E1 through E8. The fuel rods in each group are separated by a first and relatively narrow distance 80. In-between the respective groups the rod separation is greater. For example, the rod separation between groups E3 and E4 is illustrated at 82. While it is not the purpose of this application to explain the theoretical nuclear efficiencies of such a fuel design, it can be seen the spacer construction technique and resulting spacer construction is capable of accommodating such a variable pitch. Likewise, the band N can admit of modification. It will be seen that the band N includes upper flow diverting tabs 90, which tabs are known in the prior art. Referring to FIGS. 7A and 7B, an alternate construction is illustrated. Specifically, certain of the tube members C have been replaced by so-called swirl vanes S. Specifically, swirl vanes S include a continuous upper grid member 100. Continuous upper grid member forms an integral part of grid G1. The respective swirl vane members S all depend at sections 101, 102, 103 on one side of tube member C and at members 104, 105, etc. on the opposite side of cylinder C. These respective members are separated from one another by gaps 110. The swirl vane members 101-105 are each twisted 360.degree. with respect to the upper and continuous grid member 100. Thereafter the respective members 101, 102, 103 are formed into a unitary and linear bottom grid member 120. This unitary grid member is appropriately notched at orthogonal notches 61 so that the resultant continuous grid member 120 mates with the lower grid G2. It can thus be seen that the disclosed swirl vane construction integrally participates in the formation of the upper and lower grids G1, G2. From the enclosed description it will be understood that this construction technique and spacer embodiment will admit of numerous modifications, such as twist angles of 270.degree., 180.degree. and 90.degree..