Abstract: A spacer grid for a nuclear reactor fuel assembly, comprising an assembly of two families of thin partitions which are respectively parallel in each family and perpendicular from one family to the next and which bound pockets of square section through each of which a fuel rod of the cluster extends, the walls of the pocket being formed with bearing points to retain the fuel rods of the cluster, wherein it comprises bearing bridges formed by profiled bosses produced in pairs on a sheet metal tongue obtained by making two longitudinal parallel slots in the thin partition on either side of such bosses, the bosses being oppositely directed in two adjacent pockets, and the reaction of the fuel rods on the bosses after they have been positioned in the grid produces a torque on the resilient sheet metal tongue, the deformation of the tongue thus enabling the assembly tolerances of the fuel rods to be absorbed in the grid. Application to nuclear reactor assemblies.

Abstract: Device for the dismantlable fixing of a guide tube in a recess provided for this purpose in the end piece of a fuel assembly of a nuclear reactor, particularly of the water-cooled type, wherein the guide tube has an end fitting, whose ferrule-like end has an inner cylindrical profile slotted over its entire length into a certain number of flexible sectors which can be engaged in an annular recess, or on a bore having circular engagement threads on its surface, under the pressure of an internal cylindrical locking ring, means also being provided for braking the locking ring in axial translation with respect to the end piece and for remotely ensuring the dismantling of the ring.

Abstract: It has two groups of thin partitions, which are parallel in one group and perpendicular from one group to the next, which are grooved and nested to define square cavities. Support points are made in the walls of the cavity to hold in place the fuel elements. In each group, a thin partition is constituted by two superimposed sheets. The height of the first sheet is equal to double the height of the second sheet. A first sheet is positioned above the second sheet in one of the groups and below the latter in the other group. Each second sheet is nested into the first sheet of the other group.

Abstract: Water-cooled nuclear reactor fuel assembly of the type comprising two end pieces, respectively an upper end piece and a lower end piece, said end pieces having openings for the circulation of the light cooling water, the spacing grids made from a single metal have a relaxation effect under irradiation and are constituted by two groups of perpendicular plates, said grids defining cavities, each of which is traversed either by a fuel rod, or by a connecting rod, said spacing grids being distributed along the connecting rods, the walls of each cavity having bearing members for holding in place the fuel rods, wherein the fuel rods are jointed to an end piece and wherein means are provided for maintaining the group of grids against one of the upper or lower end plates, both during the operation of the reactor and when it is shut down.

Abstract: End fitting for the fuel assembly of a nuclear reactor comprising in per se known manner a device for holding the fuel assembly against an upper or lower plate of the reactor core, wherein the maintaining device is constituted by a plurality of rigid levers, having a first end and a second end, each lever being articulated on an axis A, a closed recess provided in the sides of a frame of the end fitting for each lever and elastic means contained in the recesses and exerting a restoring torque on the corresponding lever.

Abstract: Device for fixing a zircaloy guide tube of a fuel assembly of a pressurized ordinary water nuclear reactor to the steel end plate thereof.This device comprises a ring nut having two threads with opposite pitches, a screwdriver sleeve with teeth, integral in rotation with a pole but mobile in translation by means of an elastic return system along the said pole between a first low position in which the teeth carried by the said screwdriver sleeve are located in recesses in the upper part of the ring nut, which they thereby lock in rotation with the pole and the end fitting and a second upper position in which the teeth are disengaged from the recesses and where the ring and end fitting rotate independently of one another.Application to fuel assemblies of nuclear reactors of the PWR type.

Abstract: The present invention relates to a spacer grating for fuel element in a nuclear reactor of the PWR type, said grating being constituted by intersecting plates. Over the greater part of the walls equipped with springs, double springs comprise two active parts on either side of the wall on which the double spring is placed, allowing the symmetrical action of this spring on two different pencils inside two adjacent cells. On the other walls equipped with springs, single springs comprise one active part only, disposed in one of the two cells separated by the wall on which is placed the spring of which the other part is not capable of coming into contact with a fuel pencil. The invention is particularly applicable to the manufacture of fuel assemblies in nuclear reactors of the PWR type.

Abstract: A spacer grid assembly provides elastic support and secure positioning of fuel elements in a nuclear reactor. This spacer grid assembly comprises two families of thin perforated sheets, the sheets of one family being parallel to each other and perpendicular to the sheets of the other family. The interlaced assembly of these interfitting sheets forms a three-dimensional lattice of square-sectioned cells for positioning and securing the fuel elements vertically. This spacer grid assembly comprises large recesses within the cell walls that define the spring means. The spring means comprises two plates shaped as a flexible vault, a sheet stud connecting these plates, and two triangular strips integral with this sheet stud on one side and opposite each other on this same side, and ending in circular and protruding pads. These pads contact the fuel element and transmit the bearing power of the spring means to the fuel element.

Abstract: The present invention relates to a device for fixing a spring to a spacing grid for fuel elements of nuclear reactors.This device is characterized in that it is constituted by two retaining bridges (8) for the spring (6) made in one of the thin metal sheets constituting the grid and maintaining the spring (6) against said sheet. Two other bridges (10) located outside the bridges (8) constitute abutments for stopping the translation of the spring (6). A double stamping (12) made in the thin metal sheet at the approaches of each retaining bridge (8) constitute a precise translation guide for the spring (6).Application to the spacing grids of fuel elements of nuclear reactors.

Abstract: The present invention relates to an anti-fly-off device for the fuel element of a nuclear reactor.This device, which is applicable to a nuclear reactor, comprises a plurality of sheathed fuel elements kept parallel to one another by a system of spacing grids and a stucture, independent of the fuel elements and formed by two parallel plates, namely an upper plate and a lower plate, between which extend brace rods regularly distributed among the system of fuel elements, whereby at least certain of these brace rods are surrounded by grid sleeves. A casing introduced into the grid sleeves of the lower grid around the brace rods and fixed by its lower end to the lower plate has at its upper end an outer shoulder which, with an appropriate clearance, blocks the upward displacement of the grid sleeve.

Abstract: Method for fixing a zircalloy guide tube of a nuclear reactor fuel assembly to the steel end plate of said assembly, wherein the following stages are successively formed:the previously expanded end of the guide tube is engaged around a sleeve until it abuts against a first outer shoulder of said sleeves;said end is covered with a force-fitted ferrule and the tube is squeezed against the sleeve, then the upper end of the ferrule is welded to the sleeve above the said first outer shoulder;the sleeve--tube--ferrule assembly is introduced into an opening provided for this purpose in the end plate and having a shoulder, until a second outer shoulder of the sleeve abuts against the said shoulder of the end plate opening;the upper part of the sleeve is welded to the upper part of the opening of the end plate of the assembly.The invention also relates to an apparatus for fixing the zircalloy guide tube to the steel end plate.

Abstract: The spacer grid for a nuclear reactor fuel assembly has an open structure constituted by an array of flat sheet metal members in interfitting relation and defining compartments. Narrow corrugated strips project into the interior of the compartments and form separations between openings of substantial width in the surface of the sheet metal members and an outer frame surrounds the structure. The sheet metal members are joined to the corrugated strips by means of a zone having lower mechanical strength so as to increase the deflection of each strip in respect of the same applied force.

Abstract: Spacing grid for a group of fuel rods in a nuclear reactor assembly which comprises an assembly of two groups of thin sheets which are parallel within each group and perpendicular from one group to the next for defining cavities of square cross-section, each of which is traversed by a fuel rod, while substantially in the center of its extension in the region defining two adjacent cavities on either side of the sheet the latter has at least one elastically sprung tongue connected to the sheet and made from a material which differs from that of the sheet, each tongue being bent so as to give a zig-zag profile so that it has at least two bosses bearing respectively against the rods passing through the two cavities, wherein the ends of the tongue are disposed in the plane of the sheet and are engaged in slots provided in the latter in order to hold the tongue in place, while permitting a deflection of its ends as a result of the forces exerted by the rods on the bosses.