Abstract: The present invention relates to a fuel assembly with a substantially square cross section for a light-water reactor. The light-water reactor comprises a plurality of fuel rods extending between a top tie plate and a bottom tie plate. A fuel rod comprises a cladding tube which surrounds a column with fissionable material. According to one aspect of the invention, at least one fuel rod is provided with an axial gap in the fissionable material. Around this axial gap, the mass of the material is greater than the mass of the material in the main part of the cladding tube.

Abstract: A fuel assembly for a boiling water reactor where the fuel assembly during operation is arranged vertically in the core of the reactor. The fuel assembly comprises a plurality of vertical fuel rods (22) arranged in one or more fuel bundles, wherein at least the majority of the fuel rods comprise a stack of fuel pellets (7) surrounded by a cladding tube (8b) and a plenum tube (23) which is connected to the upper part of the cladding tube (8b), the plenum tube having a cross-section area which is smaller than the cross-section area of the cladding tube.

Abstract: A fuel assembly for a boiling water reactor comprises a plurality of first full-length fuel rods arranged in an orthogonal lattice, wherein each fuel rod is included in two rows of fuel rods perpendicular to each other, and a number of second fuel rods arranged in parallel with the first fuel rods and having the length considerably smaller than the length of the first fuel rods. The second fuel rods are arranged in the lower part of the fuel assembly in the space which is formed between a number of first fuel rods located adjacent to each other, that is, in a position which does not belong to the orthogonal lattice.

Abstract: A spacer for retaining and positioning elongated elements at one or a plurality of levels in a nuclear reactor fuel assembly comprises a grid structure of joined-together sleeve cells. A coolant is adapted to flow upwards through the fuel assembly. The majority of the sleeve cells are provided with an upstream edge with a waveform. The edge is waveformed in such a way that the upwardly flowing coolant first encounters a peak of the wave which is disposed between the joints of the sleeves and thereafter a valley of the wave which is disposed at the joints of the sleeves. The peaks are arranged closer to a center of the sleeve cell than the valleys. Between the peaks and valleys, oblique edges are formed.

Abstract: A fuel assembly for a boiling water reactor comprises a bottom tie plate, a top tie plate, and a first and a second group of vertical fuel rods, each including a column of fuel pellets surrounded by a cladding tube. The second group of fuel rods has a shorter active length than the first group of fuel rods. Both the first and the second group of fuel rods extend between the bottom tie plate and the top tie plate. The second group of fuel rods comprises a fission gas plenum surrounded by a plenum tube arranged above the cladding tube. The main part of the plenum tube has a cross-section area which is smaller than the cross-section area of the cladding tube.

Abstract: A nuclear fuel core in a pressurized-water reactor including fuel assemblies, each of which comprise a top tie plate; a bottom tie plate, the top tie plate and the bottom tie plate having through-openings for passing coolant flowing from beneath upwards through each of the fuel assemblies; elongated elements, arranged between the top tie plate and the bottom tie plate; a mixing cross section having a mixing center, the mixing cross section extending through four orthogonally arranged fuel assemblies and having a size corresponding to at least that of two fuel assemblies; and a plurality of spacers for retaining and mutually fixing the elongated elements, the plurality of spacers having flow control members for controlling coolant flow around the mixing center. A nuclear fuel core in a boiling water reactor is also disclosed.

Abstract: A spacer for retaining a number of elongated fuel rods into a bundle to be placed in a nuclear reactor of BWR or PWR type. The bundle is intended to be traversed in the longitudinal direction by a coolant. The spacer includes a number of cells for the fuel rods surrounded by an outer frame which is formed from a first band standing on edge. This band has possibly been extended by a skirt arranged on the upstream side of the spacer. The band or skirt edge of the spacer located on the upstream side thereof is provided with guiding tabs which are formed from plate flaps which lie in planes which extend in parallel with the flow direction of the coolant and one side edge of which slantingly extends from the first band or skirt edge in an upstream direction towards the center of the spacer.

Abstract: Spacers (10) with a cell-formed lattice-work for retaining parallel elongated elements such as fuel rods (5) into a bundle in a nuclear reactor fuel assembly are arranged in a suitable spaced relationship to each other along the bundle, and the cells are formed from tubular sleeves (1). Each one of these sleeves (1) offers a passage for one of the elements in order to fix the elements in relation to each other. Substantially half the number of sleeves (1) in a spacer (10), distributed evenly over the cross section of the bundle, are located in a first plane across the bundle and are joined to each other inside a first frame (11) surrounding the bundle, thereby forming a lattice of sleeves (1) and gaps (13). The remaining sleeves (1) of the spacer (10) are joined together inside a second frame (12) surrounding the bundle and are located in a second plane, separate from the first plane, across the bundle.

Abstract: A spacer for a nuclear reactor fuel assembly includes a cell-formed lattice-work for retaining parallel, elongated elements such as fuel rods (4) into a bundle of substantially square cross section. The cells are formed from tubular, preferably round sleeves (1). Each one of these offers a passage for one of the elements for mutually fixing these elements. Each spacer is formed from two sub-spacers (5) somewhat spaced-apart from each other in the longitudinal direction of the bundle. A first sub-spacer in a pair fixes elements lying substantially on one side of a diagonal through the bundle, and a second sub-spacer fixes the other elements such that elements passing through the sleeves (1) of the first sub-spacer pass, possibly with some exception, at the side of the sleeves in the second sub-spacer and vice versa.

Abstract: A spacer for retaining parallel, elongated fuel rods includes a plurality of cells which are formed from tubular sleeves internally provided with fixed supports and at least one spring arranged opposite to the fixed supports. The spring is intended to make contact with a fuel rod inserted into the sleeve and is formed as a leaf spring which is cut out of the wall of the sleeve and which, when the sleeve is empty, is bent into the sleeve. The leaf spring is adapted, in tensioned position when the fuel rod is inserted into the sleeve, to be returned to a position substantially coinciding with the wall of the sleeve.

Abstract: A method and a device for controlling the coolant flow to the fuel rods (1) in the fuel assembly of a pressurized-water reactor, fuel assembly including an elongated bundle of control rod guide tubes and fuel rods (1) which is arranged between a top nozzle and a bottom nozzle. The bundle is retained by spacers (2) supported by the control rod guide tubes and the top and bottom nozzles are provided with a plurality of openings for the coolant flow. According to the invention, the coolant flow along the fuel rods (1) of a fuel assembly which is under low load is reduced by the insertion of special, or the activation of existing, throttle or guide members (10,11,12,13,16) on the spacers (2) or on the fuel rods (1) between the spacers (2) such that the coolant flow is diverted to one or more adjacent fuel assemblies.

Abstract: A fuel assembly for a light-water nuclear reactor includes a plurality of vertical fuel rods (10, 42) which are arranged, in spaced relationship in a lateral direction, between a bottom tie plate (11, 44) and a top tie plate (12, 43), the bottom tie plate, defining through-going vertical channels (50) for conducting water through the bottom tie plate and into the spaces between the fuel rods. The bottom tie plate also defines horizontal channels (51, 52) which cross the vertical channels and which are preferably arranged, at edges (54) on the bottom tie plate, in open communication with the spaces between the fuel rods. Helical springs (61, 62) with horizontal symmetry axis are arranged in at least some of the horizontal channels where the horizontal channels cross the vertical channel so as to trap debris in the water passing upwardly through the through-going vertical channels.

Abstract: A fuel assembly (1) for a nuclear reactor of pressurized-water type with a number of fuel rods (2) retained into a bundle by means of spacers (3) between a top nozzle (4) and a bottom nozzle (5) which includes a plurality of openings for a coolant flow to the fuel rods (2). A partial fuel box (7) is providing at at least the lower part of the fuel assembly and extending from the bottom nozzle (5) and at least up past the lowermost ordinary spacer (3) of the bundle.

Abstract: A fuel assembly for a boiling water nuclear reactor contains a plurality of vertical fuel rods, which are arranged between a bottom tie plate and a top tie plate in a surrounding vertical casing part. At its lower end the casing part is connected to a bottom part which is provided with an inlet opening for water for conducting water in through the bottom tie plate, through the space between the fuel rods in the vertical casing part and out through the top tie plate. A debris catcher with a low flow resistance to water is provided below or above the bottom tie plate and at a distance from the bottom tie plate.

Abstract: A fuel assembly for a nuclear reactor is provided with a number of parallel fuel rods, which are retained by means of spacers (2), and guide tubes (3) between the fuel rods. The guide tubes (3) are also attached to the spacers (2) as well as to a top nozzle and a bottom nozzle (4, 5). The guide tubes (3) are provided, at least at the spacers (2), with external threads (7) for improved fixing to the spacers.

Abstract: A fuel assembly for a light-water nuclear reactor contains a plurality of vertical fuel rods which are arranged, mutually spaced from each other in the lateral direction, between a bottom tie plate and a top tie plate. The bottom tie plate is provided with through-holes for conducting water through the bottom tie plate and into the spaces between the fuel rods. The through-holes in the bottom tie plate have parts, the centre lines of which are displaced in relation to each other or make an angle with each other.

Abstract: A fuel assembly in the form of an elongated channel having several corners is connected to a coolant intended to flow through the channel. A bundle of similarly elongated fuel rods, retained by a plurality of spacers, is arranged in the channel, and arranged in the upper part of the fuel assembly, at least between a pair of spacers, is a sleeve formed of a sheet around the bundle. The sleeve has an external shape which conforms closely to the walls of the fuel assembly and is perforated by a large number of openings, the total surface of which is at least as large as the sheet surface remaining on one side of the sleeve.

Abstract: The invention relates to a fuel assembly in the form of an elongated channel having several corners. The channel is connected to a coolant intended to flow through the channel. A bundle of similarly elongated fuel rods, retained by a plurality of spacers (8), is arranged in the channel. The spacer (8) has an outer frame which is provided all around with a plurality of windows (10). According to the invention, deflection fins (9) are placed in said window and are so directed that cooling water flowing along the wall of the fuel assembly is diverted in a direction towards the center of the channel to improve the cooling for those fuel rods which are located in this region.

Abstract: The invention relates to a fuel assembly in the form of an elongated channel having several corners. The channel is connected to a coolant intended to flow through the channel. A bundle of similarly elongated fuel rods, retained by a plurality of spacers (8), is arranged in the channel. The spacer (8) comprises a number of cells surrounded by an outer frame which is formed from a band placed on edge. According to the invention, the band is extended on the upstream side of the spacer (8) by a skirt (12), in which openings (13) are provided. In certain of these openings deflection fins (14) have been arranged in order to deflect coolant, flowing along the assembly wall (6), in a direction towards the center of the respective spacer (8).

Abstract: In a BWR- or PWR-type nuclear reactor, the fuel rods in the fuel assembly are cooled by a coolant flow which is pumped through the fuel core. Depending on the degree of burnup of the fuel rods, the coolant flow to the fuel assemblies may need to be changed for the cooling to be matched to local need. To control coolant flow on the basis of the degree of burnup of the fuel rods, the irradiation growth of elongated elements in the fuel assembly has been utilized.