Abstract: The top nozzle (6) of the fuel assembly includes a transverse adaptor plate (6a) penetrated by openings (8) for fastening the guide tubes (4) and by openings (9) for water to pass through. The water passage openings (9a) in the adaptor plate (6a) of the top nozzle (6) which are arranged in a central part of the adaptor plate (6a) have a triangular shape with rounded corners and are distributed regularly around at least some of the openings (8) for fastening the guide tubes (4).

Abstract: The fuel assembly includes an arrangement for quickly fixing the guide thimble into an opening passing through the adaptor plate of a dismountable nozzle of the assembly. This arrangement includes at least two bearing stops inside the opening of the nozzle, a bearing sleeve integral with the end of the guide thimble and a locking ring which includes stops for bearing on bearing surfaces of the stops inside the opening of the nozzle and deformable elastic parts capable of being accommodated in cavities of the opening of the adaptor plate or of the bearing sleeve, in order to place the ring in a position in which the guide thimble is locked or unlocked. The sleeve includes a rim for bearing on a bearing surface of the adaptor plate at the periphery of the opening.

Abstract: The spacer grids consist of interlaced metal straps defining a regular lattice of cells. A spring for holding a fuel rod against bearing stops is fixed on at least one wall of each of the cells. In its part which constitutes the wall of the cell, the strap includes at least one stop produced by cutting and pushing the metal of the strap into the cell, so as to limit the displacement of a fuel rod housed in the cell. Stops for limiting the displacement of the fuel rod are placed preferably o the walls of the peripheral cells or corner cells of the spacer grid, opposite a peripheral belt of the spacer grid. The invention also relates to a fuel assembly which includes, in addition to structural spacer grids, end grids and additional mixing grids interposed between the structural spacer grids.

Abstract: The fuel assembly includes an arrangement for quickly fixing the guide thimble into an opening passing through the adaptor plate of a dismountable nozzle of the assembly. This arrangement includes at least two bearing stops inside the opening of the nozzle, a bearing sleeve integral with the end of the guide thimble and a locking ring which includes stops for bearing on bearing surfaces of the stops inside the opening of the nozzle and deformable elastic parts capable of being accommodated in cavities of the opening of the adaptor plate or of the bearing sleeve, in order to place the ring in a position in which the guide thimble is locked or unlocked. The sleeve includes a rim for bearing on a bearing surface of the adaptor plate at the periphery of the opening.

Abstract: Each of the square top nozzles (26) of the fuel assemblies of the core includes four locating openings (40) in the vicinity of the vertices of the nozzle. The set of locating pins (35) of the upper core plate (32) includes four pins at each of the positions of fuel assemblies which are intended to be engaged in the four openings (40) of the top nozzle (26). The locating openings (40) of the nozzle may consist of the internal bores of sleeves (36) which are fixed on the nozzle in an axial arrangement and holds the spring leaves (38) of the nozzle. The locating openings may also be machined inside four bosses, projecting at the upper part of the assembly, and each arranged in one corner of the assembly.

Abstract: An eddy-current probe (10) is moved in the axial direction of the clad of the rod (1), a first position of the probe (10) is determined in the axial direction, for which a signal from the probe is representative of the presence of the internal surface of the bottom end plug of the rod (1) and at least one second position for which the signal from the probe is representative of the presence of the end part of the spring of the fuel rod (1) or of the internal surface of the top end plug of the fuel rod (1). The total length and/or the length of the fissile stack are calculated from the first position and from the second position of the probe (10). The measurements may be performed inside the spent fuel storage pond of a reactor.

Abstract: A spacer grid spring (6) consists of a single metal leaf including two end parts (6a, 6b) substantially in the same plane and a central part (6c) out of the plane of the end parts (6a, 6b). At least one of the end parts (6a, 6b) is laterally provided with two flanges (6d, 6e) folded out of the plane of the end part (6a, 6b), in the opposite direction from the central part (6c) of the spring (6). The call wall (5) intended to receive the spring (6) includes, in an arrangement adjacent to each of two dimples (7a, 7b) placed at the ends of the wall (5), a part (8a,8b) for holding an end (6a, 6b) of the spring, and an opening (10a, 10b) passing through the wall (5) adjacent to the holding part (8a, 8b).

Abstract: The lower part (31) of the pole (10) carries an expansible bush (40) engaged and fixed on the outer surface of the part (31) by one of the ends (41) of the bush and comprising longitudinally extending slots defining resiliently bendable strips. A group of balls (39) mounted to be radially movable in openings (38) in the lower part (31) of the pole (10) and bearing against the bendable strips of the expansion bush are movable between a retracted position and a position for expanding the bush (40), by a cylindrical cam (36) connected to an actuating rod (20). The device permits inserting the locking sleeve (8) in the guide tube (13) without risk of deformation of the end strips of the guide tube (13).

Abstract: A method of excavating an underground area liable to flooding or collapsing during excavation, wherein the area is susceptible to disaggregation by high pressure water jet and is located above rock of strength suitable for drifting a gallery comprises drifting a gallery in the rock beneath the area, freezing at least a perimeter of the area to form a frozen perimeter, and excavating material from within the frozen perimeter using a high pressure water jet and one or more boreholes between the gallery and the area. Preferably the whole area is frozen for excavation.

Abstract: The device comprises a platform (13) fixed in a horizontal position on a support structure (3) for the fuel assembly (4) placed under water in a pool (1). The platform (13) includes a table (14) for shifting a carriage (35) in two crossed directions in a horizontal plane and an arrangement (27) for clamping the fuel assembly so as to immobilize it in the machining position. The fuel assembly (4) is placed in the machining position by a hoisting device (6). A table (15) mounted on the table (14) for movement in one of said crossed directions in the horizontal plane is returned elastically (40) in the direction toward the assembly (4). A frame (16) is fixed on the table (15) and permits shifting a tool-carrying carriage (49) in a direction defined by the frame (16). A motorized grinding unit (17) is fixed on the tool-carrying carriage. The device may be used in particular for cutting or levelling the surface of a spacer-grid (8) of a used fuel assembly (4).

Abstract: The duplex tube (1) comprises a tubular core (2) and a cladding or covering layer (3) made from an alloy, the base metal of which is identical to the base metal of the alloy constituting the tubular core (2).

Abstract: Oxidation treatments by ionic bombardment or post-discharge result in the formation on the surface of passivatable metals and alloys of a layer of oxide having a thickness of a few micrometers which protects the substrates from subsequent corrosion. The gas activated by the electric discharge is put in contact with the surface of the part (2) to be oxidized, which is brought to a temperature of 350.degree. to 650.degree. C. The treatment may be employed in particular for forming a protective covering on an element or a complete framework composed of a zirconium alloy of a fuel assembly of a water-cooled nuclear reactor.

Abstract: The adaptor plate (11) comprises ribs (12) which are substantially perpendicular to its faces, projecting from its lower face, delimiting between them cells and zones (15) into each of which emerges a plurality of through-openings (16) of substantially square cross-section which are arranged in a predetermined pattern.

Abstract: The device comprises a cradle (4) having at least one supporting surface on which the object (6) rests, at least one flange (5) pivotably mounted on the cradle (4) and members (14, 16, 20) for locking the flange (5a, 5b) in its turned-down position. The device further comprises a bearing block (38) connected to the flange in an articulated manner, a shoe (40) mounted on the bearing block (38) for limited displacement and having two bearing surfaces (40a) directed towards the object (6), in the turned-down position of the flange, and a leaf spring (41) interposed between the bearing block (38) and the shoe (40).

Abstract: The device (25, 26) comprises a tubular body (40) mounted axially movable on a flange (5) of a transport structure (4) for an object (6), a spring (36) for return of the tubular body (40) towards an unclamped position, an arrangement for manual displacement (19, 20, 16, 21) of the tubular body (40) between its unclamped position and a clamping position, carried by the flange (5), a rod mounted slidably in the axial direction of the tubular body (40) to a limited extent and carrying a shoe (14, 15), and a second spring for elastic return interposed between an abutment fastened to the tubular body (40) and the end of the sliding rod opposite the shoe (14, 15).

Abstract: The fuel element is inserted into a cell, under water, in a pool. Compressed air is injected into the cell so as to drain it of water. A pressure lower than atmospheric pressure is established in the cell and then the gases contained in the cell are subjected to a stream of scavenging air and are collected in a fission product detecting unit. Water is introduced into the cell, the water in the cell is sampled, fission products in the water sample are detected and the fuel element is extracted from the cell if the possible presence of a leak from this fuel element is determined. The detection device comprises a cell having an elongate body delimiting a central housing for a fuel element and end parts. One of the end parts, traversed by a channel in the extension of the housing, receives a cap for opening and closing the channel associated with a remotely controllable opening and closing arrangement.

Abstract: The duplex tube (1) comprises a tubular core (2) and a cladding or covering layer (3) made from an alloy, the base metal of which is identical to the base metal of the alloy constituting the tubular core (2).

Abstract: The nozzle (8) comprises a transverse element consisting of a cross-braced structure (14) comprising wall elements (15) delimiting cells (16) of large dimensions. Ends of a plurality of mutually parallel leaves (18) are fixed to the inside walls of each of the cells (16) so that their faces are substantially parallel to the direction of circulation of the cooling water through the nozzle (8). The leaves (18) provide between them spaces of a width which is less than the size of the particles likely to be entrained in the cooling fluid and to lodge in the fuel assembly.

Abstract: For each of the demountable fuel rods (23), the end part of the protective tube (27), which end part is open towards the exterior, has a reduced diameter over a certain length and comprises at least one seating which does or does not pass through its wall. The end part of the fuel rod (23) is integral with a ferrule (34) which is coaxial with the fuel rod and which surrounds the assembly rod (31) of the fuel rod over part of its length. The ferrule (34) is engaged on the reduced-diameter part of the protective tube (27) when the rod (31) is screwed into the bore (28) of the protective tube. Locking against rotation of the fuel rod in the protective tube (27) is ensured by deformation of the ferrule (34) within the openings of the end part of the protective tube (27). The fuel rod is demounted by exerting a torque on it by way of an engagement surface (37), for example of prismatic form, located near the end of the fuel rod.

Abstract: The lower end nozzle (1) comprises an adaptor plate (2), supporting feet (3) and a particle retention device (6) consisting of a filter plate pierced with holes and attached to the bottom face of the adaptor plate (2) over a substantial portion of its surface.