Patent Number: 
Section: description

Referring now to the drawings, particularly to FIG. 1, there is illustrated a conventional boiling water/nuclear fuel bundle, generally designated 10, comprised of a plurality of fuel rods 12 disposed in a rectilinear array thereof and extending between upper and lower tie plates 14 and 16, respectively. As illustrated, a plurality of spacers S are axially spaced one from the other at various elevations along the fuel bundle. The fuel rods and spacers are enclosed within a fuel channel 18. As conventional, the boiling water/moderator flows upwardly through the fuel bundle about the fuel rods and through the cells of the spacers S, generating steam for the generation of power. Also illustrated in FIG. 1 are part-length fuel rods 20 which terminate at their upper ends short of the upper tie plate and typically below one or more of the upper spacers. Also illustrated in FIG. 1 are a plurality of conventional swirl vanes 22 disposed on the downstream side of the spacers at spacer cell locations above the part-length rods 20. Referring to FIG. 2, there is illustrated a representative spacer S which schematically illustrates cells in a rectilinear horizontal array of cells. For convenience, the rectilinear array is characterized by perpendicularly related rows and columns of cells 24, represented by x and y axes, respectively, in FIG. 2. In the illustrated spacer, a 10xc3x9710 array of spacer cells is shown with ten cells in each row (except for water rod locations, not shown). The cells may be of the ferrule type, i.e., short cylindrical tubes for receiving the fuel rods or may comprise other types such as disclosed in U.S. Pat. Nos. 5,740,218 and 5,727,039. Suffice to say that the present invention can be used with different and various configurations of cells. In FIG. 2, there is illustrated a plurality of flow diverters 26 in combination with vortex generators 28. Referring to FIG. 3, each flow diverter 26 comprises a cylindrical tube 30, preferably corresponding in diameter, in the illustrated form, to the diameter of the cell 24 (FIG. 2). The flow diverter 26 includes a plurality of tabs 32 which project laterally outwardly of the tube 30. The tabs 32 are also inclined relative to the axis of the tube 30 in an upstream direction when disposed over a cell 24. Thus, the tabs 32 are inclined downwardly, as illustrated in FIGS. 2 and 3 and form acute angles with the axis of the tubular cells 24. The lateral margins 34 of each tab 32 are shaped complementary to the arcuate outside surfaces of diagonally adjacent cells as illustrated in FIG. 5, while the distal ends 36 of the tabs 32 are likewise arcuately configured for engagement against a diagonally adjacent cell which lies both in a different row and column as the flow diverter. As best illustrated in FIG. 5, with this configuration, the tabs 32 may be interposed in the spaces between the orthogonally related rows and columns of spacer cells. To secure the flow diverter 26 to the spacer, the diverter may be welded to each of the adjacent cells in the corresponding column and row whereby the tabs 32 abut the adjacent cells. The weld joints are denoted 35 in FIGS. 7-9. Also as best seen in FIG. 5, the distal ends 36 of the tabs 32 extend laterally outwardly of the diverter tube 30 a distance beyond a straight line 40 drawn between center lines of diagonally adjacent cells. That is, the distal ends 36 of tabs 32 extend beyond straight lines 40 extending between the center axes 42 of diagonally adjacent cells and preferably abut the cell walls of a second set of diagonally adjacent cells in columns and rows not common to the column and row containing the flow diverter. With this configuration, it will therefore be appreciated that the flow through the spaces between the diagonally adjacent cells is completely diverted into the tube 30 of the diverter 26. Also illustrated in FIGS. 2-5 is a vortex generator 28 formed of a generally cylindrical tube 50 of a diameter for reception within the tube 30 of the flow diverter 26. The lower end or base of the tube 50 has laterally outward spring tabs 52 having lower surfaces 53 inclined to the axis through the tube 50. At like spacing about tube 30 of diverter 26 as the spring tabs 52 lie about tube 50, there are provided a plurality of slots 54 through diverter tube 30. By axially displacing the vortex generator 28 onto the flow diverter 26 as illustrated in sequence in FIGS. 8 and 9, the spring tabs 52 may be deflected first inwardly by engagement of the inclined surfaces 53 against the margin of tube 30 and then deflected outwardly in the slots 54 upon registration with the slots. The spring tabs/slot engagement thus maintain the vortex generator 28 assembled on the flow diverter 26 (FIG. 4). To generate a swirling flow through the flow diverter and vortex generator assembly, a plurality of swirler vanes 60 are provided adjacent the upper end of the vortex generator 28. The vanes are formed by slitting the generally cylindrical tube 50 in an axial direction through one end thereof and twisting inwardly one edge of each vane 60. For example, where four vanes 60 are used, eight slits 61 are formed through the end of tube 50. Tube material between alternate pairs of slits is removed and the remaining vanes are twisted so that one edge inclines inwardly to meet at its end the inner edges of other vanes. By forming the vanes in this manner, the vanes lie within the tubular envelope defined by tube 50, i.e., the vanes do not extend outside the periphery of tube 50 and lie within its peripheral confines. Preferably, the tip of each vane 60 along its inner edge contacts one another at an apex 62. The apices of the vane 60 may be welded at that location 62. Thus, it will be appreciated that the vanes impart a swirling motion to the boiling water/moderator flowing upwardly in the fuel bundle through the flow diverter 26 and into vortex generator 28, i.e., flowing in a downstream direction. Thus, a swirl-type flow above the assembly and in the void region above the part-length fuel rods is achieved. Note that by employing a suitable tool, not shown, the spring tabs 52 can be deflected inwardly to release the vortex generator from the flow diverter in situ and even after irradiation. To install the flow diverter/vortex generator, the flow diverter 26 is first applied over the upper or downstream end of a cell as illustrated in FIG. 6. Note that the tabs 32 extend between the diagonally adjacent cells and that their distal ends 36 are in contact with diagonally adjacent cells (FIG. 5). Welds are formed between the sides of the tubes 30 and the adjoining cells 24 in the rows and columns to secure the flow diverter to the spacer. The vortex generator 28 is then displaced axially on top of the flow diverter as illustrated in FIG. 8. Thus, as the lower end of tube 50 is received within tube 30, the springs 52 deflect inwardly and then, outwardly into slots 54 upon registration therewith to secure the vortex generator to the flow diverter as illustrated in FIG. 9. Turning now to the embodiment hereof illustrated in FIGS. 10-12, the flow diverter 80 is constructed similarly as the flow diverter 26 except that, instead of slots 54, threads 81 are formed about the tube 30, the tabs 32 being identical as those of the previous embodiment. Vortex generator 82 is likewise formed similarly as the vortex generator 28, except that spring tabs 52 are omitted in favor of complementary threads 84. The vortex generator 82 thus may be threaded into the flow diverter 80 and released therefrom by unthreading action in situ and after irradiation. The vanes 60 of vortex generator 82 are formed similarly as the vanes of the prior embodiment. Note also that the reaction force on the vortex generator 82 indicated by the arrow 86 resulting from swirling the flow in the direction illustrated by the arrow 88 in FIG. 11 tends to tighten the threads 84 of the vortex generator 82 about the threads 81 of the flow diverter 80. The threads 81 and 84 preferably comprise male/female threads, respectively, although the threads may be arranged vice-versa. Referring now to the embodiment hereof illustrated in FIGS. 13-15, there is illustrated a combined flow diverter/vortex generator and cell assembly 96 formed of a single integral piece of tubular sheet metal stock. For example, the tabs 100 of like configuration as the tabs 32 of the first embodiment are struck from the tubular body 98 to project laterally outwardly and at an angle to the tube axis as illustrated from a review of FIGS. 14 and 15. The tabs 100 have side and end configurations similarly as in the tabs 32 of the first embodiment, but leaving holes 102 in the tubular body 98 to receive the deflected flow generated by the tabs for flow in a downstream direction within the tubular body. The upper end of the tubular body 98 comprises the vortex generator 99 (FIG. 13) which includes vanes 60 constructed similarly as the vanes of the first embodiment. In this form, the lower tubular base of the assembly below the slots 102 forms a cell of the spacer disposed above a part-length fuel rod. That is, the tubular assembly 96 is substituted for a tubular cell 24 in the spacer S and forms an integral part therewith, i.e., by welding. Consequently, the boiling water/moderator flows in a downstream direction through the tubular body 98 and is joined by the deflected flow caused by the projecting tabs 100 for flow through the assembly and the vortex generator portion thereof. The vanes 60 impart the swirling motion to the flow, as represented by the circular arrow 108 in FIG. 13, similarly as in the first embodiment. FIG. 14 illustrates the cuts 106 formed in the tubular body 98 such that the tabs may be struck and laterally projected from the body as illustrated in FIG. 15. Referring to the final embodiment of the present invention illustrated in FIGS. 16 and 17, there is provided a flow diverter 120 for use in conjunction with a cell 24 which receives a fuel rod 12. The flow diverter 120 comprises a cylindrical or tubular body 122 similarly as the tube 30 of the first embodiment for securement on the top of a cell 24, also as in the embodiment of FIGS. 2-9. Thus, body 122 includes tabs 124 constructed similarly as tabs 32 and which project into the spaces between the cells. The boiling water/moderator is thus diverted from flowing between the cells into an annular space between the flow diverter 120 and a fuel rod 12 within the cell 24 thus increasing in flow velocity and pressure, e.g., xe2x80x9csuperchargingxe2x80x9d the flow. In FIG. 17, it will be appreciated that the base of the flow diverter includes a plurality of upstream extending projections 128 whereby the flow diverter may be secured, for example, by welding along the upper margin of a cell of the spacer. The cell flow diverter 120 may be located at any position in the spacer where it is desirable to increase the flow about the fuel rod extending through that cell location. Also, the tabs 124 can be cut to different lengths on opposite sides of one another, which when bent upwards would cause the coolant flow to swirl. Thus, as illustrated in FIG. 18, the flow diverter 150 has tabs 152 which have long and short sides or edges 154 and 156, respectively. When the tabs 152 are struck from the diverter 150, the tab twists such that flow through the diverter not only increases in velocity but is also swirled in the direction of the long sides 154 of the tabs 152. Thus, the tabs 152 are twisted to provide a swirl-type flow. 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.