Patent Number: 
Section: claims

1. A PWR nuclear fuel assembly comprising:nuclear fuel rods disposed in a substantially regular array, the array having a peripheral layer of fuel rods constituting a closed loop and an adjacent layer of fuel rods, the adjacent layer constituting a closed loop of fuel rods adjacent to and surrounded by the peripheral layer;a supporting skeleton having two nozzles;guide tubes for receiving control rods, said guide tubes interconnecting the nozzles; andspacer grids for holding the fuel rods, wherein the grids are secured to the guide tubes, the assembly further comprising:at least one lattice reinforcing device for reinforcing the support skeleton, the lattice reinforcing device comprising two sets of crossed plates that are secured to one another, the crossed plates defining between them cells for receiving guide tubes and cells for receiving nuclear fuel rods, the lattice reinforcing device having an upper end and a lower end disposed between two adjacent spacer grids,wherein the lattice reinforcing device is directly secured to the guide tubes,wherein the lattice reinforcing device does not extend between the fuel rods of the peripheral layer and between the fuel rods of the adjacent layer. 2. The assembly according to claim 1, wherein the lattice reinforcing device does not have an arrangement for mixing a cooling fluid that is to flow through the nuclear fuel assembly. 3. The assembly according to claim 1, wherein the lattice reinforcing device does not directly contact the nuclear fuel rods. 4. The assembly according to claim 3, wherein thecells for receiving nuclear fuel rods are of dimensions greater than dimensions of the fuel rods so as to receive the fuel rods with clearance. 5. A PWR nuclear fuel assembly comprising:nuclear fuel rods;a supporting skeleton having two nozzles;guide tubes for receiving control rods, said guide tubes interconnecting the nozzles; andspacer grids for holding the fuel rods, wherein the grids are secured to the guide tubes, the assembly further comprising:at least one lattice reinforcing device for reinforcing the support skeleton, the lattice reinforcing device comprising two sets of crossed plates that are secured to one another, the crossed plates defining between them cells for receiving guide tubes and cells for receiving nuclear fuel rods, the lattice reinforcing device having an upper end and a lower end disposed between two adjacent spacer grids,wherein the lattice reinforcing device is directly secured to the guide tubes,wherein the lattice reinforcing device does not have an arrangement for mixing a cooling fluid that is to flow through the nuclear fuel assembly, and wherein the lattice reinforcing device does not directly contact the nuclear fuel rods. 6. The assembly according to claim 5, wherein the nuclear fuel rods are disposed in a substantially regular array, the array having a peripheral layer of fuel rods constituting a closed loop, and wherein the lattice reinforcing device does not extend between the fuel rods of the peripheral layer. 7. The assembly according to claim 6, wherein the array has a layer of fuel rods adjacent to the peripheral layer, the adjacent layer constituting a closed loop of fuel rods adjacent to and surrounded by the peripheral layer, and wherein the lattice reinforcing device does not extend between the fuel rods of the peripheral layer and between the fuel rods of the adjacent layer. 8. The assembly according to claim 5, whereinthe cells for receiving nuclear fuel rods are of dimensions greater than dimensions of the fuel rods so as to receive the fuel rods with clearance. 9. A PWR nuclear fuel assembly comprising:nuclear fuel rods disposed in a substantially regular array, the array having a peripheral layer of fuel rods constituting a closed loop;a supporting skeleton having two nozzles;guide tubes for receiving control rods, said guide tubes interconnecting the nozzles; andspacer grids for holding the fuel rods, wherein the grids are secured to the guide tubes, the assembly further comprising:at least one lattice reinforcing device for reinforcing the support skeleton, the lattice reinforcing device comprising two sets of crossed plates that are secured to one another, the crossed plates defining between them cells for receiving guide tubes and cells for receiving nuclear fuel rods, the lattice reinforcing device having an upper end and a lower end disposed between two adjacent spacer grids,wherein the lattice reinforcing device is being directly secured to the guide tubes,wherein the lattice reinforcing device does not extend between the fuel rods of the peripheral layer, and wherein the lattice reinforcing device does not directly contact the nuclear fuel rods. 10. The assembly according to claim 9, wherein the array has a layer of fuel rods adjacent to the peripheral layer, the adjacent layer constituting a closed loop of fuel rods adjacent to and surrounded by the peripheral layer, and wherein the lattice reinforcing device does not extend between the fuel rods of the peripheral layer and between the fuel rods of the adjacent layer. 11. The assembly according to claim 9, wherein the lattice reinforcing device does not have an arrangement for mixing a cooling fluid that is to flow through the nuclear fuel assembly. 12. The assembly according to claim 9, whereinthe cells for receiving nuclear fuel rods are of dimensions greater than dimensions of the fuel rods so as to receive the fuel rods with clearance. 13. The assembly according to claim 1 wherein the lattice reinforcing device is directly secured to the guide tubes by welding. 14. A method for making an assembly according to claim 1 comprising directly securing the lattice reinforcing device to the guide tubes by tube expansion. 15. A method for making an assembly according to claim 1 comprising directly securing the lattice reinforcing device to the guide tubes by sleeving.