Abstract: A fuel assembly for nuclear reactors comprising a skeleton having two end pieces connected together by elongate elements and several grids spaced apart along the guide tubes and forming cells for holding a bundle of fuel elements in position at the nodes of a regular lattice. The grids comprise median grids adapted for resisting lateral shocks and having fins for creating turbulences in the flow of the coolant along the assembly, bottom grids without fins and ensuring the cross bracing of the elements and top grids with fins and ensuring cross bracing of the elements, the top and bottom grids imposing on the coolant a pressure loss lower than the median grids.

Abstract: A nuclear fuel assembly comprises a bundle of elongated fuel rods distributed at nodes of a regular lattice and a structure for retaining said fuel rods. The structure has a lower end piece, and upper end pieces, tie rods connecting said end pieces and grids distributed along the tie rods for maintaining the fuel rods at the nodes. The structure consists of two substructures slidable with respect to each other in the direction of the fuel rods. Springs located between the two substructures spread apart the two end pieces for respective abutment against a lower core plate and an upper core plate.

Abstract: A nuclear fuel assembly for a spectral shift reactor has an upper end piece and a lower end piece secured to a structural element belonging to the upper end piece by guide tubes arranged for receiving a cluster of control elements. The upper end piece further comprises a support member arranged for receiving said cluster at the end of the fall thereof, means for guiding said support member. The support member is guided for movement parallel to the axis of the guide tubes. Springs are contained within the end piece and disposed between the structural member and the plate for braking the cluster at the end of the fall thereof.

Abstract: A spacing grid is provided for a nuclear fuel assembly comprising two sets of intersecting metal plates having fins and defining fuel element receiving pockets. The plates comprise solely half-fins each associated with a single pocket of the grid, disposed in opposed pairs at the angles of the pockets, the half-fins of one pocket being placed at 90.degree. from the half-fins of adjacent pockets.

Abstract: A device for inspecting the rods of a cluster which is insertable into the core of a nuclear reactor has a body with a guide for indexing the cluster in m different angular positions. The body includes a support plate which is traversed by the rods during movement in the body and carries n/m eddy current coils (n being the total number of rods in the group). The device is associated with a data processor and with ultrasonic and optical examination systems. Optical examination is carried out on one rod at a time while it is moved longitudinally through the body.

Abstract: The apparatus is intended for rebuilding an assembly comprising a skeleton formed by two end members connected by tie rods attached to the end members and grids distributed between the end members along the tie rods and adapted to retain a cluster of fuel rods trapped between the end members. The apparatus comprises a first chamber (AI) for receiving a fuel assembly, a second chamber (AS) for receiving a new skeleton, a repair station comprising a lift adapted to receive the two vertically disposed aligned chambers and to bring the chambers to a level such that there subsists a layer of protective water above the rods, a transfer tool (106) to draw one fuel rod at a time into the skeleton from the assembly contained in the first chamber, and means for mounting the end members on the skeleton.

Abstract: For manufacturing zirconium alloy plates, more particularly for forming grids for holding nuclear fuel elements, a strip is obtained by hot rolling, then cold rolling, with a high cold hammering rate, then the strip is subjected to reheating for removing the tension at a temperature lower than the recrystallization temperature. Plates are cut out in the transverse direction of the strip.

Abstract: A device for moving a cluster of nuclear reactor control elements, more especially usable for changing the moderation rate of a nuclear reactor, comprising a vertical shaft having nippers cooperating with grabs integral with sub-clusters. Each grab comprises resilient fingers engageable with the nippers and lockable by snap fitting on the fixed upper structure. Each nipper is formed so as to engage resilient fingers and unlock them from the upper structure when the nipper is raised above the position which causes locking of the grab on the structure. A fixed lower structure is provided for causing forced disengagement of the nipper when this latter is lowered beyond the rest position of the grab on this structure. Raising of the nipper then drives the grab by simple bearing force.

Abstract: A nuclear fuel rod has a sheath closed by end plugs and a stack of fuel pellets in the sheath. The stack is retained in abutment against one of the end plugs during handling of the fuel rod by a radially expandable element having a cross-sectional area in rest condition such as it frictionally engages an internal surface of said sheath. When the fuel rod is brought to the reactor operating temperature, the radially expandable element is contracted clear of frictional contact by temperature responsive means of a shape memory alloy operatively associated with said radially expandable element and having a transformation temperature above atmospheric temperature.

Abstract: A sipping test for detecting defective sheaths in a nuclear fuel assembly is carried out by increasing the pressure of the gases within the sheaths by increasing the temperature. The fission products are released in case of sheath failure. A mixture of water and inert gas is introduced into a hood containing the fuel assembly. Gas and water are separated at the upper portion of the hood and are circulated in distinct loops for continuous detection of the water-soluble fission products and the gas-driven fission products.

Abstract: Defective fuel elements in an assembly immersed in a liquid are detected using ultrasonic absorption. A train of ultrasonic waves having a frequency and duration such that propagation takes place as Lamb waves is applied to an end portion of the sheath. The echoes are detected. Transmission and detection are repeated for different frequencies. Some frequencies are in a range corresponding to absorption by water which may be contained in the sheath. Other frequencies correspond to a range for which there is an echo at a mechanical defect of the sheath, such as a crack.

Abstract: An ultrasonic transducer carried by rod means of dimensions such that it may be inserted in the assembly between an end piece and the caps of the element, and a crossed movement moving mechanism for bringing the transducer above the different elements. It further comprises a mechanism for moving rod elements in the longitudinal direction of the fuel elements. The transducer is set up on rod elements with at least one degree of freedom about a shaft transversal to the fuel elements so as to be able to be applied flat against the end face of a cap.

Abstract: A nuclear reactor has a stationary horizontal core plate and a plurality of upright nuclear fuel assemblies all having the same cross-section and located side by side in a regular polygonal network. Each fuel assembly either has two locations for elongated plug elements or is adjacent a fuel assembly having such locations. A device for holding down the fuel assemblies comprises a plurality of locking sets each having at least one deformable locking member and a rigid member one of which is carried by a fuel assembly and the other by the core plate. The deformable locking member is so located with respect to a location and with the associated rigid member that insertion of an elongated element into the location forces the deformable locking member into positive engagement with the associated rigid member.

Abstract: The nuclear fuel assembly comprises a bundle of fuel elements some of which contain a burnable neutronic poison, held in position at the nodes of a regular lattice by a skeleton having end pieces connected together by guide tubes occupying some of the nodes of the lattice. All the poison-containing elements are disposed so as to act on the reactivity of the adjacent assemblies in the heart of the reactor.

Abstract: A hold down device for a nuclear reactor of the type in which a plurality of assemblies are disposed between an upper plate and a lower plate, which hold down device comprises a member having at least two resilient means, for example leaf springs which, when the device is placed between the top of a first fuel assembly and the upper plate, and downward pressure is applied to the member, are applied against fuel assemblies adjacent the first fuel assembly.

Abstract: A nuclear fuel assembly comprises two end pieces connected by guide tubes. Grids are distributed along the guide tubes and define passages distributed according to a regular pattern. Some of the passages receive the tubes. Other passages retain fuel elements parallel to the tubes. Individual sleeves containing a burnable poison are carried by the tubes, each in a space bounded by one grid on one side, by an other grid or an end piece on the other side. The length of the sleeves is selected for allowing differential thermal expansion of the tubes and grids. One end of each sleeve may be secured to lugs of an associated grid.