Patent Number: 
Section: claims

1. A bottom end-piece of a support skeleton for a fuel assembly of a light water nuclear reactor, the bottom end-piece comprising:direction nozzles directing the flow of water of the reactor along the lower longitudinal ends of fuel rods supported by the skeleton, the direction nozzles being arranged at nodes of a substantially regular network of the skeleton so as to be placed in a longitudinal continuation of at least some of the fuel rods and/or at least some connection elements extending between the bottom end-piece and a top end-piece of the support skeleton, andan anti-debris device delimiting water flow channels, at least some of the water flow channels being arranged at the nodes of the substantially regular network and each including one of the direction nozzles arranged at least partially in a corresponding one of the water flow channels, the direction nozzles arranged at least partially in the water flow channels and the anti-debris device delimiting water passages therebetween, the anti-debris device and a corresponding one of the direction nozzles at at least one of the water passages delimiting a first section and a second section which are mutually offset radially relative to a central axis of the corresponding direction nozzle and form a baffle,wherein the at least one water passage is delimited such that water passing longitudinally through the water passage cannot pass rectilinearly. 2. The bottom end-piece according to claim 1 wherein the anti-debris device and the corresponding direction nozzle at the at least one water passage further delimit a third section, the third section being radially offset relative to the second section with respect to the central axis of the corresponding direction nozzle, the first section, the second section and the third section following each other in order to form two successive baffles of opposing directions. 3. The bottom end-piece according to claim 1 wherein the at least one water passage surrounds the corresponding direction nozzle. 4. The bottom end-piece according to claim 1 wherein the at least one water passage has a downstream portion diverging in the flow direction of the water. 5. The bottom end-piece according to claim 1 wherein the at least one water passage has an upstream portion converging in the flow direction of the water. 6. The bottom end-piece according to claim 1 wherein the direction nozzles and the anti-debris device are integral. 7. The bottom end-piece according to claim 1 wherein the bottom end-piece comprises at least one additional grid for retaining debris which is fitted upstream and/or downstream of the water passages. 8. The bottom end-piece according to claim 1 further comprising at least one debris retaining sleeve extending longitudinally between the downstream end of the at least one water flow channel and a block covering the corresponding direction nozzle. 9. The bottom end-piece according to claim 8 wherein the sleeve comprises a zone which has no water flow opening and which delimits a cavity for trapping debris with the corresponding direction nozzle. 10. The bottom end-piece according to claim 1 further comprising a device laterally retaining the lower longitudinal ends of substantially all the fuel rods. 11. The bottom end-piece according to claim 10 wherein the retention device includes holes for receiving the lower longitudinal ends of the fuel rods which are provided in blocks which cover the direction nozzles. 12. A fuel assembly for a nuclear reactor, the assembly comprising:fuel rods including lower end plugs at lower longitudinal ends thereof; anda skeleton for supporting the fuel rods, the fuel rods extending in a longitudinal direction and being arranged at nodes of a substantially regular network of the skeleton, the support skeleton comprising a bottom end-piece and a top end-piece and elements for connecting the end-pieces, the fuel rods being arranged longitudinally between the end-pieces, the bottom end-piece comprising:direction nozzles directing the flow of water of the reactor along the lower longitudinal ends of the fuel rods supported by the skeleton, the direction nozzles being arranged at the nodes of the substantially regular network so as to be placed longitudinally below the fuel rods or elements for connecting the end-pieces in a longitudinal continuation of at least some of the fuel rods and/or at least some connection elements extending between the bottom end-piece and the top end-piece of the support skeleton, andan anti-debris device delimiting water flow channels, at least some of the water flow channels being arranged at the nodes of the substantially regular network and each including one of the direction nozzles arranged at least partially in a corresponding one of the water flow channels, the direction nozzles arranged at least partially in the water flow channels and the anti-debris device delimiting water passages therebetween, the anti-debris device and a corresponding one of the direction nozzles at at least one of the water passages delimiting a first section and a second section which are mutually offset radially relative to a central axis of the corresponding direction nozzle and form a baffle. 13. The bottom end-piece according to claim 1 further comprising blocks receiving the lower longitudinal ends of at least some of the fuel rods. 14. The bottom end-piece according to claim 13 wherein the direction nozzles extend downward from the blocks into the anti-debris device. 15. The bottom end-piece according to claim 14 wherein the fuel rods include lower end plugs at the lower longitudinal ends thereof, the blocks receiving the lower end plugs. 16. The bottom end-piece according to claim 1 wherein a bottom of the anti-debris device is below the direction nozzles. 17. The bottom end-piece according to claim 1 wherein the corresponding direction nozzle and the anti-debris device are configured such that the first section is above the second section and the first section is positioned a greater distance from the central axis of the corresponding direction nozzle than the second section. 18. The bottom end-piece according to claim 17 wherein the corresponding direction nozzle and the anti-debris device are configured such that an outer diameter of the second section is less than or equal to an inner diameter of the first section. 19. The bottom end-piece according to claim 1 wherein the anti-debris device includes a grid of partitions, at least two of the partitions forming one of the water flow channels, the at least two partitions varying in thickness to form the first and second sections. 20. The bottom end-piece according to claim 19 wherein the at least two partitions each include a protrusion preventing the water passing longitudinally through the water passage from passing rectilinearly. 21. The bottom end-piece according to claim 20 wherein the at least two partitions each includes a top portion above the protrusion and a bottom portion below the protrusion, each of the top portion and the bottom portion being thinner than the protrusion.