Abstract: An absorber cluster for a nuclear reactor includes at least a first absorber assembly and a second absorber assembly. Each absorber assembly respectively comprises neutron absorbing elements. Absorber elements of each of the first absorber assembly and the second absorber assembly are made from the same material or the same combination of materials selected from the group of neutron absorbing materials consisting of a first europium hafnate, a second europium hafnate, a first samarium hafnate, a second samarium hafnate, hafnium carbide, and samarium hexaboride. The first europium hafnate and the second europium hafnate have different compositions. The first samarium hafnate and the second samarium hafnate have different compositions. The absorber elements of the first absorber assembly have a cross-sectional structure different to that of the absorber elements of the second absorber assembly.

Abstract: A method for thermochemically treating a part while masking a portion and corresponding mask are provided. The method includes the steps of providing a mask comprising a body with a seat, at least a deformable sealing washer located in the seat, and a tightening bushing, the body having a cavity, placing a first portion of the part in the cavity, a second portion of the part being located in a passage in the sealing washer, and a third portion of the part being located outside the mask, moving the tightening bushing to its tightened position so that the sealing washer is deformed and applied against the second portion of the part, and applying a thermochemical treatment to the third portion of the part.

Abstract: An absorber cluster for a nuclear reactor includes at least a first absorber assembly (22) and a second absorber assembly (24). Each absorber assembly respectively comprises neutron absorbing elements (20). Absorber elements (20) of each of the first absorber assembly (22) and the second absorber assembly (24) are made from the same material or the same combination of materials selected from the group of neutron absorbing materials consisting of a first europium hafnate, a second europium hafnate, a first samarium hafnate, a second samarium hafnate, hafnium carbide and samarium hexaboride. The absorber elements (20) of the first absorber assembly (22) have a cross-sectional structure different to that of the absorber elements (20) of the second absorber assembly (24).

Abstract: A fuel rod cladding (4) for a light water reactor includes a core (16) including a matrix consisting of pure molybdenum or of a molybdenum-based alloy; and an outer protective layer (18). The outer protective layer (18) is selected among a chromium-based coating (20) deposited on an outer surface of the core (16) that includes at least one chromium-based coating layer (24) consisting of pure chromium or of a chromium-based alloy; a chromium-based diffusion layer (22) obtained by diffusion of chromium into the core (16) from the outer surface of the core (16); or a succession of a chromium-based diffusion layer (22) obtained by diffusion of chromium into the core (16) from the outer surface of the core (16) and a chromium-based coating (20) consisting of chromium or of a chromium-based alloy deposited on the outer surface of said core (16).

Abstract: A method for thermochemically treating a part while masking a portion and corresponding mask are provided. The method includes the steps of providing a mask comprising a body with a seat, at least a deformable sealing washer located in the seat, and a tightening bushing, the body having a cavity, placing a first portion of the part in the cavity, a second portion of the part being located in a passage in the sealing washer, and a third portion of the part being located outside the mask, moving the tightening bushing to its tightened position so that the sealing washer is deformed and applied against the second portion of the part, and applying a thermochemical treatment to the third portion of the part.

Abstract: A method for producing a wear-resistant and corrosion-resistant stainless steel part for a nuclear reactor is provided. This method includes steps of providing a tubular blank in austenitic stainless steel whose carbon content is equal to or lower than 0.03% by weight; shaping the blank; finishing the blank to form the cladding; hardening the outer surface of the cladding by diffusing one or more atomic species; the blank, before the providing step or during the shaping or finishing step, being subjected to at least one hyper quenching with sub-steps of: heating the blank to a sufficient temperature and for a sufficient time to solubilize any precipitates present; quenching the blank at a rate allowing the austenitic structure to be maintained in a metastable state at ambient temperature and free of precipitates.

Abstract: A method for thermochemically treating a part while masking a portion and corresponding mask are provided. The method includes the steps of providing a mask comprising a body with a seat, at least a deformable sealing washer located in the seat, and a tightening bushing, the body having a cavity, placing a first portion of the part in the cavity, a second portion of the part being located in a passage in the sealing washer, and a third portion of the part being located outside the mask, moving the tightening bushing to its tightened position so that the sealing washer is deformed and applied against the second portion of the part, and applying a thermochemical treatment to the third portion of the part.

Abstract: A method for surface processing at least a portion of a component of zirconium or hafnium alloy, including at least one operation of nanostructuring a surface layer of the alloy so as to confer on the alloy over a thickness of at least 5 ?m a grain size which is less than or equal to 100 nm, the nanostructuring being carried out at a temperature which is less than or equal to that of the last thermal processing operation to which the component was previously subjected during its production. Component of zirconium or hafnium alloy processed in this manner.

Abstract: A grid including at least two meshed grid parts intended to be superposed in a longitudinal direction, each grid part extending in a transverse plane, and the grid parts being moveable one relative to the other in at least one transverse direction between an open configuration for the insertion of nuclear fuel rods in the longitudinal direction through the grid parts, and a closed configuration allowing each fuel rod inserted through the grid parts to be clamped transversely between the grid parts. According to one aspect of the invention, the grid includes elements for transversely immobilizing the grid parts in the closed configuration, the immobilizing elements being designed to engage as the superposed grid parts are moved closer together in the longitudinal direction.

Abstract: A method for thermochemically treating a part while masking a portion and corresponding mask are provided. The method includes the steps of providing a mask comprising a body with a seat, at least a deformable sealing washer located in the seat, and a tightening bushing, the body having a cavity, placing a first portion of the part in the cavity, a second portion of the part being located in a passage in the sealing washer, and a third portion of the part being located outside the mask, moving the tightening bushing to its tightened position so that the sealing washer is deformed and applied against the second portion of the part, and applying a thermochemical treatment to the third portion of the part.

Abstract: A method for producing a wear-resistant and corrosion-resistant stainless steel part for a nuclear reactor is provided. This method includes steps of providing a tubular blank in austenitic stainless steel whose carbon content is equal to or lower than 0.03% by weight; shaping the blank; finishing the blank to form the cladding; hardening the outer surface of the cladding by diffusing one or more atomic species; the blank, before the providing step or during the shaping or finishing step, being subjected to at least one solution annealing with sub-steps of: heating the blank to a sufficient temperature and for a sufficient time to solubilise any precipitates present; quenching the blank at a rate allowing the austenitic structure to be maintained in a metastable state at ambient temperature and free of precipitates.

Abstract: A method for producing a wear-resistant and corrosion-resistant stainless steel part for a nuclear reactor is provided. This method comprises steps of providing a blank in stainless steel; shaping the blank; finishing the blank to form the part in stainless steel, the finishing step allowing the prevented onset or the removal of work hardness on the outer surface of the part; hardening the outer surface of the part via diffusion of one or more atomic species.

Abstract: A method for surface processing at least a portion of a component of zirconium or hafnium alloy, including at least one operation of nanostructuring a surface layer of the alloy so as to confer on the alloy over a thickness of at least 5 ?m a grain size which is less than or equal to 100 nm, the nanostructuring being carried out at a temperature which is less than or equal to that of the last thermal processing operation to which the component was previously subjected during its production. Component of zirconium or hafnium alloy processed in this manner.

Abstract: A grid including at least two meshed grid parts intended to be superposed in a longitudinal direction, each grid part extending in a transverse plane, and the grid parts being moveable one relative to the other in at least one transverse direction between an open configuration for the insertion of nuclear fuel rods in the longitudinal direction through the grid parts, and a closed configuration allowing each fuel rod inserted through the grid parts to be clamped transversely between the grid parts. According to one aspect of the invention, the grid includes elements for transversely immobilizing the grid parts in the closed configuration, the immobilizing elements being designed to engage as the superposed grid parts are moved closer together in the longitudinal direction.

Abstract: A control cluster for a pressurized water nuclear reactor comprising a bundle of neutron-absorbing rods each of which comprises a metal tube called cladding which is sealed off by a top end plug at its top end and by a bottom end plug at its bottom end and has a support, or spider, of radiating shape to which the absorber rods are attached through their upper end plugs, characterized in that the cladding of at least some of the absorber rods is weld-free hafnium tubes, the top end plugs of the absorber rods having hafnium cladding being of titanium-based alloy and being welded to the top end part of the hafnium cladding of the absorber rod, the bottom end plugs being of massive hafnium and being welded to the bottom.

Abstract: A control cluster for a pressurized water nuclear reactor comprising a bundle of neutron-absorbing rods each of which comprises a metal tube called cladding which is sealed off by a top end plug at its top end and by a bottom end plug at its bottom end and has a support, or spider, of radiating shape to which the absorber rods are attached through their upper end plugs, characterized in that the cladding of at least some of the absorber rods is weld-free hafnium tubes, the top end plugs of the absorber rods having hafnium cladding being of titanium-based alloy and being welded to the top end part of the hafnium cladding of the absorber rod, the bottom end plugs being of massive hafnium and being welded to the bottom

Abstract: After a nuclear reactor has been stopped and allowed to cool down following a period of operation, action is taken in a pool of the nuclear reactor on at least one guide tube of the activated upper internal equipment of the nuclear reactor to enlarge (21b, 21c) guide channels (16b, 16c) of the guide tube (8) in at least one continuous guidance zone. The enlargement is preferably performed by machining discontinuous cavities along the length of the guide channel (16b, 16c). Enlargement is preferably performed on the guide tube (8) in place within the upper internal equipment that has been placed on a storage stand in the reactor pool.

Abstract: After a nuclear reactor has been stopped and allowed to cool down following a period of operation, action is taken in a pool of the nuclear reactor on at least one guide tube of the activated upper internal equipment of the nuclear reactor to enlarge (21b, 21c) guide channels (16b, 16c) of the guide tube (8) in at least one continuous guidance zone. The enlargement is preferably performed by machining discontinuous cavities along the length of the guide channel (16b, 16c). Enlargement is preferably performed on the guide tube (8) in place within the upper internal equipment that has been placed on a storage stand in the reactor pool.

Abstract: The absorber rod comprises cladding (12) of stainless steel closed by plugs (14, 16) and containing a column of absorber pellets (24) e.g. of boron carbide. It also has an end bar (26) of hafnium secured to the bottom plug by a purely mechanical connection.

Abstract: Surface preoxidation of the substrate is carried out by bringing the substrate into contact with an oxidizing gas excited by a cold plasma, the substrate being situated in the flowing afterglow of the cold plasma used to excite the oxidizing element and being heated to an oxidation temperature of less than 500.degree. C. A metal oxide is formed at the surface of the preoxidized substrate by heterogeneous oxidation of a metal halide with a gas mixture including an oxidizing element activated by a cold plasma. The oxidizing gas mixture is brought into contact with the halide as directly as possible in the vicinity of the substrate arranged in the far flowing afterglow of the cold plasma. The cold plasma is preferably generated by microwaves. The process can be used in particular for producing a protective coating on a cladding tube of a nuclear fuel rod.