Patent Number: 048270636
Section: description

Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a nuclear reactor fuel assembly intended for a pressurized water reactor having two square retainer plates 2 and 3 made of metal, which are parallel to one another. FIG. 1 also shows two guide tubes 4 and 5 made of metal, each of which accommodates one control rod. The longitudinal axes of the guide tubes pass through the two retainer plates 2 and 3 at an angle of 90.degree. and are each screwed firmly to one of the retainer plates 2 and 3 at each end. Each guide tube 4 and 5 is guided through a square space or mesh opening in square, lattice-like spacers 6 having outer and inner sheet-metal ribs 6a and 6b, which are located along the length of the guide tube 4 between the two retainer plates 2 and 3 and are retained in a force-locking manner, such as by being firmly welded on the guide tubes 4 and 5. A force-locking connection is one which connects two elements together by force external to the elements, as opposed to a form-locking connection which is provided by the shapes of the elements themselves. Fuel rods 8 are guided through each of the other spaces or mesh openings of the spacers 6 and are parallel to the guide tubes 4 and 5. Each fuel rod 8 is substantially formed of a cladding tube filled with nuclear fuel and closed in a gas-tight manner at both ends. The fuel rods 8 are not secured to either of the two retainer plates 2 and 3. Instead, the fuel rods 8 are retained in the spaces or mesh openings of the spacers 6 in an elastic manner, that is in a force-locking manner, by means of non-illustrated springs and rigid bearing nubs of the spacers 6. The fuel rods 8 therefore have play in the direction of the longitudinal axes thereof between the two retainer plates 2 and 3 so that they can expand without hindrance in the longitudinal direction, that is in the longitudinal direction of the fuel assembly. The spacers 6, have no twisted turbulence-promoting vanes protruding beyond the sides of the spaces or mesh openings, particularly on the inner ribs 6b. The fuel assembly has an additional lattice 7 between each two spacers 6, each of which is unequally spaced apart from the two adjacent spacers 6. The additional lattices 7 have sheet-metal ribs 9 and 10 which pass through each other at right angles and on edge, forming square spaces or mesh openings, each of which accommodates one of the fuel rods 8 or a guide tube 4 or 5. While the fuel rods 8 are guided in the spaces or mesh openings of the additional lattice 7 in such a way as to be spaced apart from the sheet-metal ribs 9 and 10, that is loosely and with play, a metal sheath 11 is mounted on the guide tubes 4 and 5 by welding on the inside surface to the guide tube 4 or 5. The outer surface of the metal sheath 11 is in turn welded to four sheet-metal ribs 9 and 10 at a time, so as to form the space or mesh opening in the additional lattice 7 in which the guide tube 4 or 5 is located. As FIGS. 2 and 4 show particularly clearly, the ribs 9 that are parallel to one another have leading and trailing edges 9a and 9b, which have zig-zag portions 9c and 9d. The zig-zag portions 9c and 9d are compactly located in the plane of the associated sheet-metal rib 9 and thus of the sides of the spaces or mesh openings of the additional lattice 7 that are formed by the rib 9. The zig-zag portions 9c and 9d of the leading and trailing edges 9a and 9b of the ribs 9 are also parallel to one another. A zig-zag portion 9c having legs of equal length that form an angle of 90.degree. with one another, is located on the leading edge 9a between each two mutually parallel ribs 10. The zig-zag portions 9c are located in such a way as to face the oncoming flow direction for the coolant in a nuclear reactor. A zig-zag portion 9d which also has legs of equal length is disposed on the leading edge 9b of the ribs 9 at each of the ribs 10. One of the legs is disposed on each either side of the associated rib 10, forming an angle of 90.degree. between the two legs. Each of the zig-zag portions 9d is located in the outflow direction of the coolant flwwing through the fuel assembly in a nuclear reactor, so that the zig-zags 9c and 9d of the mutually parallel leading and trailing edges 9a and 9b of the mutually parallel sheet-metal ribs 9 of the additional lattice 7 are staggered with respect to one another. The mutually parallel ribs 10 of the additional lattice 7 have turbulence-promoting vanes 12a and 12b on mutually parallel trailing edges 10a thereof. Each two turbulence-promoting vanes 12a and 12b which are mounted next to one another face away from one another, as shown in particular in FIG. 4. This is due to the fact that they are twisted about the longitudinal direction of the fuel rods 8 and the guide tubes 4. Each edge of each space or mesh opening of the additional lattice 7 having one fuel rod 8, has two turbulence-promoting vanes 12a and 12b, each of which comes to a point at the end of the edge of the space or mesh opening and protrudes beyond the side of the space or mesh opening associated with this edge. Each side of a space or mesh opening is formed by one rib 10. As FIG. 4 shows, bending lines or deflection curves 12c and 12d at which the turbulence-promoting vanes 12a and 12b begin to protrude beyond the side of the space or mesh opening of the additional lattice 7, are of equal length and each forms the same angle .alpha. with the associated trailing edge 10a of the ribs 10. Both bending lines 12c and 12d, like the turbulence-promoting vanes 12a and 12b, are located on the outside above the trailing edge 10a of the ribs 10. Turbulence-promoting vanes of this kind may also be located on the mutually parallel leading edge of the ribs 10, which is parallel to the trailing edge 10a. The ribs 9 and 10 of the additional lattice 7 each have brackets 13 and 14 formed on the two ends thereof, which grip the additional lattice 7 inbetween the fuel rods 8 that are located at outer regions 15 and 16 of the fuel assembly. Furthermore, the sides of the ribs 9 and 10 that form the surface of the additional lattice 7 in the spaces and that are parallel to the longitudinal direction of the fuel rods 8 and the control rod guide tube 4, are advantageously smooth and/or flat (such as by dispensing with bearing nubs). This is done so that they optimally present little resistance to a flow of coolant in the longitudinal direction of the fuel assembly in a nuclear reactor. The foregoing is a description corresponding in substance to German Application No. P 36 32 627.5, dated Sept. 25, 1986, the International priority of which is being claimed for the instant application, and which is hereby made part of this application. Any material discrepancies between the foregoing specification and the aforementioned corresponding German application are to be resolved in favor of the latter.