Patent Number: 
Section: claims

1. A nuclear fuel rod spacer grid for a fuel assembly, the nuclear fuel rod spacer grid comprising at least two meshed grid parts including a first grid part and a second grid part, the first and second grid parts being superposed in a longitudinal direction, each of the first and second grid parts extending in a transverse plane, the first and second grid parts being movable relative to one another in at least one transverse direction between an open configuration for insertion of nuclear fuel rods in the longitudinal direction through the first and second grid parts, and a closed configuration allowing each rod inserted through the first and second grid parts to be clamped transversely between the grid parts, andimmobilization elements for transversely immobilizing the first and second grid parts in the closed configuration, the immobilization elements being arranged to come into engagement as the superposed first and second grid parts are brought together in the longitudinal direction, each rod being clamped transversely between a support plate of the first grid part and a support plate of the second grid part in the closed configuration. 2. The grid according to claim 1 wherein the first and second grid parts have members for locking the grid parts longitudinally in the closed configuration. 3. The grid according to claim 2 wherein the locking members are fixed to the first grid part and are capable of snapping onto the second grid part as the first and second grid parts are brought together in the longitudinal direction. 4. The grid according to claim 1 wherein the immobilization elements comprise peripheral walls fixed to the first grid part and defining a space between the peripheral walls and the second grid part, the space for receiving the second grid part, the second grid part being finable into the space. 5. The grid according to claim 4 wherein when the grid is viewed in the longitudinal direction, imaginary straight lines passing along an outer periphery of each side of the grid parts form a polygonal contour, the peripheral walls comprising at least one pair of peripheral walls fixed to the first grid part and extending along opposite sides of the first grid part. 6. The grid according to claim 5 wherein the at least one peripheral wall fixed to the first grid part has a tooth for locking the grid parts in the closed configuration, the tooth being capable of snapping onto the second grid part as the grid parts are brought together. 7. The grid according to claim 1 wherein the first and second grid part has at least one passage for a guide thimble, the guide thimble for receiving a cluster rod, the first grid part being capable of receiving the guide thimble with transverse clearance in at least one transverse direction of clamping of the rods between the first and second grid parts. 8. The grid according to claim 1 wherein each of the at least first and second grid parts are formed of first plates and second plates, the second plates intersecting with the first plates. 9. The grid according to claim 1 wherein the at least two grid parts are in pairs, a first pair being the first and second grid part and further comprising a second pair, the first pair of grid parts clamping the rods in a first transverse direction and the second pair of grid parts clamping the rods in a second transverse direction, the second transverse direction being different from the first transverse direction. 10. The grid according to claim 9 wherein the first grid part of the first pair of grid parts is fixed to a first grid part of the second pair of grid parts. 11. A nuclear fuel rod spacer framework for a nuclear fuel assembly, comprising a plurality of spacer grids for rods of a bundle of rods, the spacer grids being distributed along the rods at a distance from one another, at least one of the spacer grids being the spacer grid according to claim 1. 12. A nuclear fuel assembly, comprising a bundle of nuclear fuel rods and a spacer framework for the rods, the framework being according to claim 11. 13. The nuclear fuel rod spacer grid as recited in claim 1 wherein each of the first and second grid parts define cells therein, the cells of the second grid part being movable relative to the cells of the first grid part in the at least one transverse direction between the open configuration and the closed configuration. 14. The nuclear fuel rod spacer grid as recited in claim 13 wherein the second grid part is movable longitudinally to move the cells of the second grid part away from the cells of the first grid part from the closed configuration and into the open configuration, the second grid part being movable longitudinally to move the cells of the second grid part toward the cells of the first grid part from the open configuration and into the closed configuration. 15. The nuclear fuel rod spacer grid as recited in claim 1 wherein the second grid part is disconnected from the immobilization elements in the open configuration. 16. The nuclear fuel rod spacer grid as recited in claim 1 wherein in the closed configuration, the first grid part and the second grid part clamp a longitudinal portion of at least one of the rods such that the first grid part clamps a first circumferential portion of the longitudinal portion and the second grid part clamps a second circumferential portion of the longitudinal portion opposite the first circumferential portion. 17. The nuclear fuel rod spacer grid as recited in claim 1 wherein in the closed configuration, the first grid part and the second grid part are positioned such that the first grid part clamps each rod in a first transverse direction and the second grid part clamps each rod in a second transverse direction opposite the first transverse direction. 18. The nuclear fuel rod spacer grid as recited in claim 1 wherein during movement in the closed configuration, the second grid part moves longitudinally along the rods and gradually clamps the rods with the first grid part. 19. A nuclear fuel rod spacer grid for a fuel assembly, the nuclear fuel rod spacer grid comprising:at least two meshed grid parts including a first grid part and a second grid part, the first and second grid parts being superposed in a longitudinal direction, the second grid part being movable in the longitudinal direction relative to the first grid part in and out of a transverse plane between an open configuration for insertion of nuclear fuel rods in the longitudinal direction through the first and second grid parts, and a closed configuration allowing each rod inserted through the first and second grid parts to be clamped transversely between the grid parts, the first and second grid parts aligned coincident with each other in the transverse plane in the closed configuration such that an upper surface of the first grid part contacts a lower surface of the second grid part at the transverse plane in the closed configuration and the upper surface of the first grid part does not contact the lower surface of the second grid part at the transverse plane in the open configuration, andimmobilization elements for transversely immobilizing the first and second grid parts in the closed configuration, the immobilization elements being arranged to come into engagement as the superposed first and second grid parts are brought together in the longitudinal direction. 20. A nuclear fuel rod spacer grid for a fuel assembly, the nuclear fuel rod spacer grid comprising:at least two meshed grid parts including a first grid part and a second grid part, the first and second grid parts being superposed in a longitudinal direction, each of the first and second grid parts extending in a transverse plane, the second grid part being movable toward and away from the first grid part such that the first and second grid parts have an open configuration where the second grid part is spaced away from the first grid part for insertion of nuclear fuel rods in the longitudinal direction through the first and second grid parts, and a closed configuration where the second grid part is brought together with the first grid part and each rod inserted through the first and second grid parts is clamped transversely between the grid parts, andimmobilization elements for transversely immobilizing the first and second grid parts in the closed configuration, the first grid part being fixed to the immobilization elements in both the open and closed configurations, the immobilization elements being arranged to come into engagement with the second grid part in the closed configuration, the second grid part being spaced from the immobilization elements in the open configuration.