Abstract: The invention relates to a fuel assembly for a nuclear reactor comprising a bundle of longitudinal fuel rods which are insertable into the fuel assembly and held together by spacers (1), consisting of cells, arranged along the bundle. The wall of the fuel assembly towards the bundle of fuel rods is provided with a number of first locking members (5) arranged in the longitudial direction of the wall, and the spacers (1) are provided with a second locking member. The second locking member comprises at least two interconnected rods (3), one rod consisting of material having a low coefficient of thermal expansion and the other rod consisting of material having a high coefficient of thermal expansion. These rods have been adapted, in dependence on the temperature in the reactor in operation, to bring the second locking member into engagement with the first locking members (5) and to release the same when the reactor is shutdown.

Abstract: A bimetallic spacer for supporting fuel rods in position in a nuclear reactor fuel assembly substantially comprises inner and outer structural elements of a first metallic material and spring elements of a second metallic material. The structural and spring elements together define a lattice, the interstices of which receive the individual fuel rods. The structural elements and spring elements in the spacer are connected together by forming the structural elements with openings and fitting the ends of the spring elements in the openings. At one end of the opening in the structural element, two slots can be provided for forming a tongue-shaped member which is moved aside to make space for the spring element and then moves back when the end of the spring element is in position, thus preventing a possible vertical return movement of the end of the spring element.

Abstract: A fuel assembly for a boiling water reactor is provided with at least one vertical channel for a by-pass flow through the fuel assembly. The channel is supplied with water through a vertical supply tube surrounded by the base of the assembly, the supply tube being arranged with its lower end in the vicinity of the lower end of the base.

Abstract: A nuclear fuel assembly for a boiling reactor comprises a plurality of fuel rods arranged in four sub-bundles surrounded by a fuel channel of substantially square cross-section. A vertical channel-formed support member for the passage of water, separates the sub-bundles of fuel rods. By arranging each sub-bundle with a reduced corner portion by not locating a fuel rod in that corner of the sub-bundle towards the center of the fuel assembly, the sub-bundles can be located in a separating channel-formed support member with an enlarged central channel. The enlarged central channel makes it possible to contain a larger quantity of non-boiling water in the central part of the fuel assembly, which results in better neutron moderation in the central part of the fuel assembly.

Abstract: A nuclear fuel assembly containing a plurality of vertical fuel rods and possibly occasional vertical water-filled rods, which are surrounded by a fuel channel of substantially square cross-section and which are divided, by means of a vertical channel for water of substantially cruciform cross-section, into four sub-bundles. Each fuel rod contains a stack of circular-cylindrical pellets of a nuclear fuel arranged in a cladding tube. Each sub-bundle consists of, in all, twenty-five rods arranged in a lattice containing 5.times.5 rods. The cladding tube of each fuel rod has a wall thickness in the range 0.50 to 0.70 mm and an external diameter in the range 8.5 to 10.3 mm.

Abstract: A fuel assembly for a boiling water reactor has a fuel channel of generally square cross-section and provided with four walls, which fuel channel surrounds a plurality of fuel rods. Adjacent to its upper edge, the fuel channel is provided with a spacer having a corner portion and two arms extending from the corner portion and making an angle of 90.degree. with each other. The corner portion of the spacer engages a first corner of the fuel channel, and the two arms each make contact with the outer sides of the two fuel channel walls that meet at the first corner. Each arm is provided, at its outermost part, with a diagonally directed, horizontal projection which is inserted into a corresponding aperture in the adjacent fuel channel wall, the two projections thereby bridging across a respective one of the two corners of the fuel channel which are closest to the said first corner.

Abstract: The invention relates to a spacer arranged to retain and fix elongated fuel rods into bundles insertable into a nuclear reactor fuel assembly, said spacer being of a zirconium alloy having a low neutron absorption. To counteract play and hence wear in case of increasing burnup when the springs relax and the rod diameter is reduced by shrinkage, the spacer is made with different textures in the springs (2, 3) and the surrounding structure (1, 6). The difference in texture gives the springs a great axial irradiation growth and the surrounding structure a small axial irradiation growth, which contributes to a remaining deflection tendency of the springs in relation to the surrounding structure during the life of the fuel assembly.

Abstract: Nuclear fuel assembly having four bundles of fuel rods, at least one fuel bundle being made with twenty symmetrically arranged fuel rod positions, the number of fuel rod positions in each of the remaining fuel rod bundles being at least sixteen and at most twenty-five.

Abstract: A fuel asembly with a fuel channel (2) which surrounds a plurality of fuel rods (1) and which is divided, by means of a stiffening device (3) of cruciform cross-section and four wings (5), into four sub-channels (4) each of which comprises a bundle of fuel rods.Each fuel channel side has a plurality of stamped, inwardly-directed projections (6) arranged vertically one after the other, said projections being welded to one and the same stiffening wing. Each one of the wall portions located between the projections (6) defines, together with two adjacently positioned projections and a portion of the stiffening wing, a communication opening between two bundles located on one side each of the stiffening wing.

Abstract: A fuel assembly for a boiling water reactor is provided with at least one vertical water channel (4, 5) for a by-pass flow through the fuel assembly. At its lower end the channel is connected to a radial tube (10) which opens out at the outer side surface of the fuel assembly. Below the radial tube, the wall of the assembly base (2) is provided with a through-hole (12).

Abstract: A fuel assembly for a boiling water reactor comprises a plurality of fuel rods (2, 2'), which constitute four partial bundles and are surrounded by a fuel channel system (1) comprising one partial tube for each partial bundle. Each of the four partial bundles rests on a bottom tie plate (19) and is positioned with respect to the others by means of a common top tie plate (31), which is provided with a lifting loop (33) which is sufficiently strong to be able to lift the four partial bundles simultaneously, a major part of the lifting force being transmitted to said bottom tie plates via a plurality of supporting fuel rods (2').

Abstract: A nuclear reactor fuel assembly for a nuclear reactor comprises a housing with a wall and spacer means removably located within the housing, the spacer means comprising a plurality of spacer cells each adapted to receive an elongated fuel rod for the purpose of locating a bundle of such fuel rods in spaced-apart relationship within the housing. A portion of the housing which confronts the spacer means is provided at least at one location with a first locking means, and one of the spacer cells is provided with a second locking means movable between active and inactive positions. This second locking means is prevented from moving past the first locking means in the direction of elongation of the fuel rods when the second locking means is in its active position but is able to move past the first locking means when in its inactive position. The second locking means is moved from its inactive position to its active position by the insertion of a fuel rod into said one spacer cell.

Abstract: A boiling water reactor fuel assembly is provided with an elongated, vertical stiffening device having four stiffening wings which are each attached to a wall of the fuel box. Each stiffening wing has at least one vertically directed passageway for water.

Abstract: A fuel assembly which comprises a plurality of subassemblies of fuel rods (12), which are each enclosed in a corresponding wall system (1), is provided at its upper end with a horizontal distribution channel (22, 32), extending along the periphery, which upon emergency cooling receives sprinkling water and distributes this among the different subassemblies.

Abstract: A fuel assembly for a boiling reactor is constructed according to the accompanying drawing (FIG. 1). Preferably, only partial spacers (6) are used in the fuel assembly. Each partial spacer positions only a minor portion of the total number of fuel rods in the assembly. Groups of partial spacers are arranged axially one after the other, the partial spacers in each group being positioned at at least two different levels and together positioning all fuel rods in the fuel assembly.

Abstract: An elongated absorber plate, which is stationarily mounted in a gap between two fuel assemblies in a reactor core, comprises a plurality of absorber channels which are filled with a burnable absorber material. The channels (5b) are formed by welding to each other two confronting sheet elements (2b, 3b), of which at least one is corrugated.

Abstract: A fuel assembly for the core of a boiling water nuclear reactor has a plurality of boxes each surrounding a respective bundle of fuel rods. These boxes, are connected at one end to a common bottom unit, intended to be connected to an opening in a supporting plate in the core, and are also connected at their other end to a common top unit. The boxes may be detachably connected to the bottom portion and the top unit and be relocatable within the fuel assembly. Alternatively, the bundles of rods may be arranged for easy withdrawal from the boxes to enable transfer of the rod bundles between the boxes.

Abstract: Boiling reactor comprising a reactor vessel and a moderator tank arranged therein which surrounds a reactor core with a plurality of vertically arranged fuel boxes. A moderator tank space located below the reactor core is provided with inlet openings for cooling water streaming through the reactor core and is in direct hydraulic connection with the lower ends of the fuel boxes. The wall of the rector vessel is provided with an opening for the supply of a first feed water flow to the cooling water flowing into the lower end of the reactor core, with the upper ends of the fuel boxes being arranged in hydraulic connection with a plurality of riser tubes by the aid of which a steam and water mixture flowing out from the fuel boxes is conducted to a plurality of water separators.