Patent Number: 
Section: claims

1. An assembly intended to be inserted into a nuclear reactor, comprising:an assembly hollow body, of elongate shape along a longitudinal axis X, a wall of the hollow body comprising at least one through-opening that extends through the wall;an assembly element inserted at least in part into the hollow body, the assembly element comprising at least one flexible blade of which a free end is shaped into a clip-fastening hook collaborating in clip-fastening with the through-opening from inside the hollow body, so as to connect the assembly element to the hollow body; andat least one removable means for locking the at least one flexible blade clip-fastened into the through-opening, each of the at least one removable means for locking including a locking screw making it possible to prevent the at least one flexible blade from flexing and thus lock the connection between the assembly element and the hollow body. 2. The assembly according to claim 1, wherein the clip-fastening hook is produced by a thickening of the free end of the at least one flexible blade. 3. The assembly according to claim 1, wherein the hollow body is of hexagonal cross section and each face of the hexagon comprises one through-opening, and the at least one flexible-blade includes a flexible blade clip-fastened into each of the through-openings. 4. The assembly according to claim 1, wherein the locking screw of each of the at least one removable means for locking, when in a position in which the locking screw is screwed into the at least one flexible blade, makes it possible to prevent the at least one flexible blade from flexing and from becoming unclipped. 5. The assembly according to claim 1, wherein each of the at least one flexible blade is produced by cutting into a thickness of the assembly element. 6. The assembly according to claim 5, wherein the wall of the assembly hollow body comprises at least one open-ended bore designed to allow the locking screw to pass from the outside of the hollow body and a screw head to be housed. 7. The assembly according to claim 1, wherein each of the at least one flexible blade is attached and fixed to the assembly element by a fixing screw. 8. The assembly according to claim 7, wherein each fixing screw is welded to the assembly element and/or to the at least one flexible blade in its screwed-in position. 9. The assembly according to claim 8, wherein the assembly element comprises at least one cavity in which the clip-fastening hook can become lodged when the at least one flexible blade is in the flexed position, the locking screw being screwed through the clip-fastening hook and housed in the cavity when the at least one flexible blade is clipped in, so as to prevent the at least one flexible blade from flexing. 10. The assembly according to claim 1, wherein the assembly is a nuclear fuel assembly, the hollow body being a central portion forming a casing configured to clad fuel pins, the assembly element being an upper neutron shield (UNS) device or the assembly element forming an upper portion forming a gripper head of the assembly. 11. The assembly according to claim 1, wherein the nuclear reactor is a liquid sodium-cooled fast neutron reactor. 12. The assembly according to claim 1, wherein the assembly element includes a shoulder and, when the assembly element is inserted into the assembly hollow body, a top of the assembly hollow body abuts the shoulder of the assembly element. 13. A method for assembling the assembly according to claim 1, wherein the assembly comprises at least two of the flexible blades, the method comprising:a/ inserting the assembly element into the assembly hollow body by a translational movement, so as to achieve simultaneous flexing of the at least two flexible blades toward the inside of the hollow body, lowering of the assembly element down inside the hollow body until the at least two flexible blades return to their position with their hooks clip-fastened into the corresponding through-openings of the hollow body so as to connect the hollow body to the assembly element; andb/ locking each of the at least two flexible blades clip-fastened into the through-opening using the at least one removable means for locking. 14. A method for dismantling the assembly according to claim 1, wherein the assembly comprises at least two of the flexible blades, the method comprising:a1/ unlocking each of the at least two flexible blades, the hook of each of which is clip-fastened into the corresponding through-opening, by removing the at least one removable means for locking;b1/ applying a radial force to the hook of each of the at least two flexible blades from the outside of the through-opening, so as to cause the at least two flexible blades to flex simultaneously toward the inside of the hollow body, unclipping the hooks; andc1/ extracting the assembly element from inside the assembly hollow body via a translational movement. 15. The dismantling method according to claim 14,wherein the assembly element comprises a plurality of the flexible blades and the hook of each of the flexible bladesis individually clip-fastened into the corresponding through-opening of the hollow bodyand locked,step b1/ being performed by simultaneous actuation of actuators, and arranged individually facing one of the through-openings.