Patent Number: 058752234
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1a shows a boiling water fuel assembly 1 which comprises a long tubular container, of rectangular cross section, referred to as fuel channel 2. The fuel channel 2 is open at both ends so as to form a continuous flow passage through which the coolant of the reactor flows. The fuel assembly 1 comprises a large number of equally long tubular fuel rods 3, arranged in parallel in a bundle, in which pellets 4 of a nuclear fuel are arranged. The fuel rods 3 are arranged spaced from each other in four orthogonal sub-bundles by means of a cruciform support means 8 (see also FIG. 1b). The respective sub-bundle of fuel rods 3 is retained at the top by a top tie plate 5 and at the bottom by a bottom tie plate 6. The fuel rods 3 in the respective sub-bundle are kept spaced apart from each other by means of spacers 7 and are prevented from bending or vibrating when the reactor is in operation. The spacer according to the invention may, of course, also be used in a boiling water reactor which lacks the cruciform support means 8 and instead is provided with, for example, one or more water tubes. FIG. 2 shows a pressurized-water reactor fuel assembly 1 comprising a number of elongated tubular fuel rods 3 and control rod guide tubes 8 arranged in parallel. In the fuel rods 3, pellets 4 of a nuclear fuel are arranged. The control rod guide tubes 8 are retained at the top by a top nozzle 5 and at the bottom by a bottom nozzle 6. The fuel rods 3 are kept spaced apart from each other by means of spacers 7. FIG. 3 shows the spacer 7 which comprises an orthogonal grid structure of sleeves 9. Each sleeve 9 is intended to position an elongated element 3 extending therethrough. The elongated element 3 may consist, for example, of a fuel rod or a control rod guide tube. The sleeves 9 are thus intended to be joined together with other similar sleeves into a preferably orthogonal grid structure. At least the majority of the sleeves 9 are internally provided with four supports 10. The supports 10 comprise elongated embossments facing the center of the sleeve 9. The elongated embossments give an all-sided positioning of the elongated element 3 extending through the sleeve. The supports 10 are evenly distributed along the circumference of the sleeve 9. The supports 10 extend along the whole length of the sleeve. In FIG. 4 a fragment of the spacer according to FIG. 2 is shown in a view from above. This figure shows that the supports 10 position an elongated element 3 extending through the sleeve. FIG. 5 shows the fragment in FIG. 4 in a view from the side. The upstream edge of the sleeve 9, in relation to the coolant flowing through the assembly, is provided with a wavy form. The wavy edge of the sleeve 9 is suitably made such that that part of the upstream edge 9a, at which the sleeve is joined to an adjacently located sleeve 9 in the grid structure of the spacer, encounters the upwardly-flowing coolant after the coolant has encountered the edge 9b disposed between the joints 9a. In this way, a foreign matter which adheres to the upstream edge of the spacer is oriented transversely of the flow direction and between the elongated element 3, that is, as far away from the surface of the elongated element 3 as possible. In FIG. 4, such a foreign matter 11, in the form of a wire cutting, is shown. The captured foreign matter 11 will thus be oriented so as to make contact with that part of the wavy edge 9a which is disposed at the joint with adjacently disposed sleeves 9 in the grid structure and substantially diagonally across the flow channel 12 which is formed between the sleeves in an orthogonal grid structure. Because of the elongated and inwardly-facing supports 10, the upstream first edge 9b of the sleeve 9 is arranged making contact with the elongated element 3. In this way, foreign matter is prevented from passing in between the sleeve 9 and the elongated element 3. Oblique edges 9c, that is, edges forming an angle v with the axial direction of the spacer, are formed between the part edges 9a, 9b. The oblique edges 9c guide and orient the foreign matter so that it will make contact with the part edge 9a. In this way, the foreign matter which is stopped against the upstream edge of the spacer is diverted away from the surface of the elongated elements 3.