Patent Number: 047818859
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 having a fuel assembly top fitting 2 and a fuel assembly base 3 each having a square cross section, an elongated prismatic water pipe or water channel box 4 with a square cross section, and an elongated fuel channel 5 having a square cross section. The water pipe 4 is centrally disposed in lattice or grid-like spacers 6, which are spaced apart from one another, when viewed in the longitudinal direction of the water pipe 4. Each mesh opening or aperture in the lattice formed by these spacers 6 is penetrated by a fuel rod 7 containing nuclear fuel. For example, eight of the fuel rods 7 may be so-called supporting rods, which have threaded bolts at both ends with which they are firmly screwed to the fuel assembly top fitting 2 or base 3. The other fuel rods 7 pass loosely through openings in the fuel assembly top fitting 2 and the fuel assembly base 3, with bolts located on both ends thereof. The fuel rods are each fixed in place with a compression biased helical spring. The springs are seated on the bolts engaged in the openings in the fuel assembly top fitting 2 on the inner surface of the fuel assembly top fitting 2 and they are supported on the inner surface and on the associated fuel rod. While the fuel assembly top fitting 2 and base 3 are formed of stainless steel, the elongated fuel channel 5 is fabricated from a zirconium alloy. The fuel channe1 is open at both ends and encompasses the fuel assembly top fitting 2 and the fuel assembly base 3. The upper end of the fuel channel has non-illustrated sheet metal strips inside the corners thereof, which are firmly screwed at the upper end of stay bolts 9 to the top of the fuel assembly top fitting 2. As shown in FIG. 2, an imaginary lattice or grid is symbolized by broken lines 10 and 11 in a cross section of the fuel channel. The lines 10 and 11 are at right angles to one another and form spaces of equal volume surrounding each fuel rod or square mesh openings or apertures 12, which are rectangular at the inside of the fuel channel, in the imaginary lattice or grid in the cross section of the fuel channel. All of the lines 10 that are parallel to one another are parallel to one pair of sides of the cross section of the fuel channel, and all of the lines 11 that are parallel to one another are parallel to the other pair of sides pair of the cross section. The lattice or grid formed by the lines 10 and 11 has nine mesh openings or apertures 12 on each side of the cross section, or in other words the imaginary lattice or grid has a total of 9.times.9 mesh openings or apertures. The water pipe 4 is centrally disposed in the imaginary lattice or grid having the lines 10 and 11 and nas a square cross section. The cross-sectional sides of the water pipe are parallel to the associated adjoining cross-sectional side of the fuel channel 5. All of the cross-sectional sides of the water pipe 4 are spaced apart from the associated adjoining cross-sectional side of the fuel channel 5 by the same distance. The cross section of the water pipe 4 encompasses 3.times.3 mesh openings or apertures in the center of the imaginary lattice or grid. There are a total of 72 mesh openings or apertures of the imaginary lattice or grid located on all of the outer surfaces of the water pipe 4, between the water pipe 4 and the fuel channel 5, and one fuel rod 7 containing nuclear fuel is disposed in each of the mesh openings or apertures. Adjoining fuel rods 7 are spaced apart from one another by the same distances. As FIG. 3 shows, the water pipe 4 has an open upper end and a lower end which fits over a bottom part 14 having a circular cross section. The surface or shell of the bottom part 14 has four planar locations 15, each of which is spaced apart from the next by an angle of 90.degree. and is firmly welded to the water pipe 4. The underside or lower surface of the stainless steel bottom part 14 has a threaded bolt 16. The threaded bolt passes through an opening in the lattice-like grating on top of the fuel assembly base 3 and is firmly screwed to the fuel assembly base 3 with a non-illustrated nut. At the lower end of the water pipe 4, which is likewise fabricated from a zirconium alloy, the bottom part 14 forms four passage openings 17 for water, each being disposed between two respective planar locations 15 at the corners of the cross section of the water pipe 4. In a boiling water nuclear reactor, the water flows through the water pipe 4 from the fuel assembly base 3 toward the fuel assembly top fitting 2; the water does not evaporate in the water pipe 4 but leaves the water pipe 4 again at the upper end thereof. In a boiling water reactor, the water flowing through the nuclear reactor fuel assembly inside the fuel channel 5 on the outer surface of the water pipe 4 from the fuel assembly base 3 to the top fitting 2 enters the fuel channel 5 through the fuel assembly base 3, partly evaporates at the outside of the fuel rod 7, and finally leaves the fuel channel 5 in the form of a water and water vapor mixture through the fuel assembly top fitting 2. The foregoing is a description corresponding in substance to German application P No. 35 40 466.3, dated Nov. 14, 1985, 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.