Patent Number: 053655575
Section: description

Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there are seen four fuel rods 1, 2, 3, 4 that define a flow channel 6, and a lengthwise web 8 extending between them, to which further lengthwise webs 9 and 10 are parallel. Lateral protrusions in the form of bent-out sheet--metal strips 12, on which the fuel rods 1 and 2 are supported, are formed from the sheet metal of the web. In order to support the fuel rods 3 and 4, the lengthwise web has one spring 14 each. Reference numeral 16 indicates a lengthwise axis of the flow channel, which at the same time forms the center axis of a twisted tab having parts located on either side of the center axis that are indicated by reference numerals 19 and 20. As FIG. 2 shows, the lengthwise web is stamped from a metal sheet and has tabs 24 on an upper edge 22 thereof that taper toward their end. Web parts 25, 26 are formed onto this tapered end. The tabs are then twisted relative to the plane of the web in such a way that their ends are at right angles to the web, as is seen in FIG. 3. A sharp bend at an upper edge 28 of the web is avoided. Instead, the web in this case merges steadily and slowly with the tab. The angle of twisting of the tab relative to the web increases out of proportion to the distance from the upper edge of the web. This continuously more-severe twisting is shown quite clearly in FIGS. 4 and 5, in each of which planes are shown at which a twisting of 90.degree., 180.degree., and 270.degree. is attained. Arrows 32 and 34 shown in FIG. 1 indicate the direction of rotation of the twisting. It can be assumed that the fuel rods are disposed in square holes in an imaginary grid and that the tabs are disposed at intersections of the grid. At adjacent intersections carrying the tabs, the tabs of these two intersections are twisted in mirror fashion relative to one another, as is indicated by the arrows 32, 34. Reference numerals 38, 39 indicate weld seams, with which the web parts of the tabs that are perpendicular to the lengthwise webs are connected to the corresponding web parts on the tabs of adjacent lengthwise webs. In the embodiment shown in FIG. 1, only the maximum twisting angle of 90.degree. shown in FIG. 3 has been made. A contour of side edges 40, 42 of the tabs is selected in such a way that after the twisting, a practically constant spacing relative to the fuel rods results. FIG. 6 shows a part of a web 56 before its twisting, having tab parts 50 which merge with web parts 52, that are located in a plane in which twisting through 90.degree. relative to the web 56 is attained. The web parts 52 are welded together with the web parts 54 of the tabs of adjacent webs to make a crosswise web, as is seen in FIG. 7. The tabs of the webs 56 still have free ends 58, which extend into a plane in which the twisting amounts to 180.degree.. The contour of the tabs is selected in such a way that after the twisting, an annular space of constant width is produced between the tabs and the fuel rods. FIG. 8 shows tabs with a twisting of 360.degree.. In this case two helical windings of the twisted tab face one another in each quadrant of the flow channel, but their inclination decreases continuously, because of the increasing twisting toward the tab ends. The contour of the tab is selected in such a way that the lower winding leaves a narrower annular space free around the fuel rods, while the upper winding leaves a broader annular space free around these rods. The invention accordingly imposes an intensive spin upon a coolant flow in the various flow channels. In the process, however, the liquid is forced into the region adjacent the fuel rods, where it is needed to cool the fuel rods, and is made only slightly turbulent. There, only a slight tangential speed occurs with only slight flow resistance. However, the steam flows, virtually decoupled from the liquid flow, with a tolerable pressure loss through the center of the flow channel. Since the steam can attain high speeds and is removed quickly, the volumetric proportion of the liquid increases, and therefore the moderation of the neutrons increases as well. As a result, with pronounced cooling, good utilization of the fuel is achieved.