Patent Number: 043127053
Section: description

Referring now to the drawing and first, particularly, to FIGS. 1 to 3 thereof, there is shown a spacer grid according to the invention formed of sheetmetal webs 1 and 2. The spacer grid not only contains the fuel rods 5 but also, in a conventional manner, non-illustrated control rod guidetubes. The latter are insertable into sleeves 6 which are also shown in FIG. 1. Fixed contact elements are formed by ring-shaped tube sections 3 which are inserted into slots 32 and 31, respectively (see FIGS. 2 and 3) at the points of intersection of the webs 1 and 2. They are fastened there by welding; in addition, welded spots can also be provided at the points of intersection of these webs 1 and 2. As shown in FIG. 8, these fixed contact elements 3 are bevelled at the corners 33 thereof. This facilitates insertion thereof into the slots 31 and 32 and facilitates later insertion of fuel rods and guide tubes; furthermore, flow resistance to the coolant, which is normally water, is thereby reduced. The same purpose is served by the "arrow-shaped" construction of the webs 1 and 2 at the intersection points. Since the non-illustrated control rod guide tubes have a greater diameter than that of the fuel rods 5 and, therefore, also the receiving sleeves 6 therefor and the adjacent ring-shaped elements 3 are provided with indentations 36, as shown in FIG. 9 and, in addition, are welded at the locations of the indentations 36 to the sleeve 6 to hold the latter (note FIG. 1). The resilient contact elements 4 are inserted into cutouts 12 formed in the web sheets 1 (see FIG. 3) and are held in this position by the subsequently inserted webs 2. A metallurgical joint is unnecessary. The construction thereof can be seen in detail from FIGS. 5, 6 and 7, wherein FIG. 6 is a side elevational view, FIG. 5 a corresponding top plan view and FIG. 7 a view of the contact element 4 in direction of the web sheet 1. It is apparent especially from FIG. 5 that this contact element 4 can be made by punching or stamping and bending out of a flat metal sheet in conventional manner. The two resilient parts 41 of the contact element 4, which can also be bent differently, of course, connect a head and a base piece 42 of triangular cross section. It is unnecessary to weld these end pieces 42 because short slots 45 are machined or worked into them and, like short slots 43 and 44 formed at the transversely opposed side of the contact element 4, embrace the wall of the web 1 (note FIG. 7) when the end pieces 42 are inserted into the cutout 12 (note FIG. 3) formed in the sheetmetal web 1 and are thereby themselves also held in the intended position thereof. As mentioned hereinbefore at the introduction hereto, these resilient contact elements 4 are made of materials, such as Inconel, for example. The remaining parts of the spacer grid, however, are formed of zirconium alloy. To reduce the expenditure of material further and, thereby, the neutron absorption as well as the pressure loss in the coolant flowing through, the mesh walls 1 and 2 of the spacer grid are furthermore formed with large-area openings 11 and 22. As is evident from FIG. 1, the fuel rods 5, respectively, rest only against the rings 3 which are disposed opposite the resilient contact elements 4. However, a space remains between the fuel rods 5 and the rings 3 which are disposed above and below the spring elements 4. In this way, the respective three-point mounting is provided in each diagonal of a spacer mesh and, moreover, overstressing of the resilient parts 41, if strong lateral forces should occur, is avoided since then, further movement of the fuel rod 5 is prevented by the rings 3 which are fastened above and below the resilient contact elements 4. This meets the requirement for an earthquake-proof construction. As is also apparent from FIG. 1, it is no longer possible for the fuel rod 5 to break out of this mounting, in comparison with the proposals in the state of the art, so that also this is provided as security against lateral forces such as could occur, for instance, due to non-uniform thermal stressing or loading of the fuel rods 5. It may also be seen from the foregoing that the cooling of the fuel rods 5 within the mesh is improved over the proposals in the state of the art since, at the narrowest locations between the fuel rods 5 and the web walls 1 and 2, no bumps or springs interfering with or hindering the flow are provided. Since, due to the geometrical relationships provided there, the flow cross section for the coolant is made more uniform, the behavior of the fuel rods 5 during thermal overloads is also considerably improved. This is achieved in particular also by providing for the coolant to be able to reach the continuously endangered points of a fuel rod just behind the corresponding contact points of the spacers in an unimpeded manner and in greater quantities. It then also follows (and detailed measurements have confirmed this), that the pressure losses are lower than in the spacer constructions which were heretofore conventional. In addition to these functional improvements in spacer construction, the assembly of the thus-improved spacers is also relatively simple to effect. First, the resilient contact elements 4, completed in themselves, are inserted into the openings 11 formed in the sheetmetal webs 1 and slid into the cutouts 12 up to a stop. After all of the places for the resilient contact elements 4 are occupied, the webs 2 are inserted into the slots 21 formed in the webs 1 and surround the latter with the cutouts 22. Thereafter, the rings 3 are inserted on the upper and lower sides of the assembled spacer grid and are automatically fastened by welding. This is, of course, done with due regard being given to those meshes at which the sleeves 6 for the non-illustrated control rod guide tubes are inserted. The contact springs 41 projecting into the latter meshes are first removed from the contact elements 4. A spacer for nuclear reactor fuel assembly which is so constructed is, of course, further held together in a conventional manner by an outer enveloping web. Furthermore, conventional coolant deflection vanes can also be provided for effecting improved turbulence of the coolant and thereby not only improve the cooling effect but also render the coolant outlet temperature more uniform.