Abstract: The method includes assessing operational characteristics of the fuel assembly, the assessing including determining if the fuel assembly is to be placed in a controlled location in the reactor core, a controlled location being positioned adjacent to a control blade that is to be utilized, and configuring the sidewalls of the outer channel by making at least a first select sidewall of the outer channel a reinforced sidewall, the remaining sidewalls of the outer channel, other than the at least a first select sidewall, being non-reinforced sidewalls. The entirety of the reinforced sidewall as a whole is at least one of thicker and made from a material that is more resistant to radiation-induced deformation as compared to an entirety of the non-reinforced sidewalls.

Abstract: A fuel assembly for a nuclear power boiling water reactor including a fuel channel defining a central fuel channel axis, fuel rods, each having a central fuel rod axis, at least 3 water channels for non-boiling water, each water channel having a central water channel axis and each water channel having a larger cross-sectional area than the cross-sectional area of (the average) fuel rod. The fuel rods include a first group of full length fuel rods and a second group of shorter fuel rods. The fuel assembly comprises 3 or 4 fuel rods which belong to said second group and which are positioned such that the central fuel rod axis of each of these 3 or 4 fuel rods is closer to the central fuel channel axis than any of the water channel axes of the water channels.

Abstract: In a fuel assembly, a plurality of fuel rods are arranged in an array of 10 rows and 10 columns in the cross section of the fuel assembly. A flow resistance member is disposed in a central portion in the cross section at upper end portions of partial length fuel rods which are a part of the fuel rods. In the flow resistance member, resistance members are each disposed between ferrules arranged in an array of 6 rows and 6 columns in the diagonal direction of the flow resistance member. Resistance members are each disposed between the ferrules in a peripheral portion of the flow resistance member. By disposing the resistance members, the pressure loss in an inner region in the cross section of the fuel assembly is increased, and the flow rate of a gas-liquid two-phase flow in an outer region surrounding the inner region is increased.

Abstract: In one embodiment, a fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, a plurality of fuel rods disposed within the channel, and an internal mixer disposed within the channel above the plurality of fuel rods. The internal mixer includes peripheral flow control members and interior flow control members. The peripheral flow control members are located near walls of the channel, and the interior flow control members are located towards a longitudinal center of the housing. At least one of the peripheral flow control members is configured to direct liquid metal flowing through the channel towards an interior of the channel, and at least one of the interior flow control members is configured to direct liquid metal flowing through the channel away from the interior of the channel.

Abstract: A support grid for a nuclear fuel assembly, the fuel rod assembly having a generally cylindrical fuel rod with a diameter, wherein the support grid includes a frame assembly having a plurality of generally uniform cells, each the cell having at least one wall and a width and at least one generally cylindrical tubular member having a cell contact portion with a greater diameter and at least one helical fuel rod contact portion with a lesser diameter, the cell contact portion and the fuel rod contact portion joined by a transition portion, the greater diameter being generally equivalent to the cell width, and the lesser diameter being generally equivalent to the fuel rod diameter such that a fuel rod disposed in the tubular member would engage the inner diameter. Wherein the least one tubular member disposed in one cell of the plurality of generally square cells so that the cell contact portion engages the at least one cell sidewall.

Abstract: Disclosed is a spacer grid assembly with mixing vanes supporting fuel rods of nuclear fuel assemblies and mixing coolant that flows around the fuel rods, and more particularly, a spacer grid equipped with mixing vanes that mix coolant flowing around fuel rods. The spacer grid with hydraulically balanced mixing vane patterns, in the spacer grid equipped with a strip dividing a plurality of unit grid cells and a plurality of springs, protruded in uniform directions of vertical and horizontal directions on a grid surface of the strip and supporting nuclear fuel rods, which includes: a plurality of mixing vanes protruded to the downstream of coolant on an upper end of the inner grid surface, wherein positions and directions of the mixing vanes are formed in regular patterns on the spacer grid. Thus, it can minimize coolant flow induced vibration of the spacer grid by balancing hydraulic load generated by the mixing vanes, around the center of the spacer grids.

Abstract: A nuclear fuel assembly including: a casing delimiting an inner space divided into a central part as a fissile zone, in which a bundle of nuclear fuel pins is located, an upper part, and a lower part; a lower end including a coolant supply inlet; an upper end including a coolant evacuation outlet; pins in a bundle of pins including an upper and/or a lower plenum; a mechanism creating a communication with the lower part of the inner space of the casing with the zone surrounding the assembly, as an inter-assembly zone, through the wall of the casing; and an upper neutron protection mechanism inside the casing.

Abstract: A protector bottom grid for a nuclear fuel assembly that includes three laterally staggered and horizontally oriented protrusions that extend into the fuel rod cell of a support grid below a vertically oriented spring. The three staggered protrusions extend into the cell a distance that maintains a space between the protrusions and the fuel rod. The vertically oriented spring biases the fuel rod against a dimple extending from the opposite cell wall that is at an elevation just above the spring. The protrusions below the spring trap incoming debris in the area of the fuel rod end cap and protect the fuel rod cladding from fretting.

Abstract: In a nuclear reactor core, a lower tie plate assembly is provided with asymmetric features designed to control or vary a loss coefficient as a function of rotation of the associated fuel assembly. An associated method is provided to control the flow of coolant through the associated fuel assembly via rotation of the fuel assembly relative to the fuel support member. Control of the flow can be used to adjust assembly flow rate, assembly power and flow quality within the fuel assembly, among other assembly operational characteristics. Such flow control will impact the flow through other assemblies as well, since core flow remains generally fixed. On a core-wide basis, such flow control can be used to optimize core wide parameters. Optimization parameters of particular interest are the fuel cycle cost and moisture carryover.

Abstract: A nuclear fuel assembly bottom nozzle, of the type including a perforated plate to allow water to pass through it, the nozzle having lateral faces, and at least one anti-debris element positioned on a lateral face to block out debris likely to infiltrate between the bottom nozzle and another adjacent bottom nozzle, characterized in that, in the free state, the or each anti-debris element permanently projects from the lateral face on which it is positioned, the or each anti-debris element being elastically deformable so as to retract towards the lateral face in the event of a force being exerted on the anti-debris element towards the lateral face.

Abstract: This invention relates to nuclear engineering and may be used in structures of nuclear fuel assemblies, especially those used in PWR and BWR nuclear reactors. A fuel assembly comprises spacing grids comprising cells formed by orthogonal crossing plates. An insertable spacing element is installed in each cell, which is designed for fixing the fuel rod passing through the cell. In the spacing grids that are arranged between the first spacing grid and the last spacing grid downstream the coolant flow at least some cells, through which the fuel rods pass, are provided with deflectors designed for mixing the coolant flow. The insertable spacing element comprises a shell, which has a cross-section in the form of an octagon formed by four facets that are rounded and convex in the direction from the center of said element and by four facets located therebetween that are shaped and concave toward the center of the said element.

Abstract: A bi-alloy spacer grid (BASG) is provided with grid straps and springs made using different zirconium alloys. The grid straps are made from a relatively low growth zirconium alloy, and the springs are made from a relatively high growth zirconium alloy. The springs are coupled to the grid straps by welding, mechanical interference, or secondary forming in place. When subjected to irradiation, the springs grow relative to the grid straps thereby maintaining contact with the fuel rod cladding, while the grid straps resist growth to maintain structural stability of the entire fuel assembly. The optimized balance of the high growth springs and low growth grid straps mitigates the formation of gaps between the fuel rods and grid support structures). The growth properties of the grid straps and springs may be further controlled through optional different fabrication processes.

Abstract: A spacer for a fuel assembly of a boiling water reactor has a frame formed of outer webs and inner webs disposed crosswise relative each other. Gills are disposed on the exterior of the outer webs. The exterior of the outer webs of the spacer is provided with a plurality of projections in the form of bulges in the wall. The bulges project outwardly by a greater distance than the gills.

Abstract: A spacer grid having tunable mixing vanes for optimizing coolant flow is provided for a nuclear fuel assembly. The mixing vanes include an upper piece and a lower piece, which are coupled to a middle ligament that is coupled to the top or downstream portion of one or more of the grid straps forming the spacer grid. The upper piece, lower piece, and middle ligament are bent, rotated, and/or twisted into various positions to more effectively mix the coolant and affect the coolant's flow as it moves upwards through the fuel assembly. For example, in one embodiment, the mixing vane has an “S” shape wherein the middle ligament is positioned parallel to the longitudinal axes of the fuel rods of the fuel assembly, the upper piece bends towards one of the fuel rods, and the lower piece bends away from the fuel rod. In this manner, optimized even and sustained mixing of the coolant is provided.

Abstract: A spacer grid for a fuel assembly in a light-water-cooled nuclear reactor, for providing the transverse retention of a bundle of fuel rods in mutually parallel arrangements, having an array of cells juxtaposed and placed in a regular lattice, each bounded and separated from neighboring cells by at least one peripheral wall which is open at two opposed ends, along the direction of an axis of the cell, so as to receive a fuel rod of cylindrical general shape passing along the cell along its axis parallel to the peripheral wall.

Abstract: A spacer for a fuel element of a boiling water reactor contains cells that are formed by inner partitions, which are disposed in a crisscross manner, and by outer partitions, which surround the inner partitions in a frame-like manner. A guiding device is placed on the spacer and contains a flow-through opening, which is located in an outer partition. The guiding device also contains a guiding element which, when viewed in the direction of flow of the coolant, is located in front of the flow-through opening, and is situated at a distance from the inner side of the outer partition, and interacts with the flow-through opening like a venturi nozzle.

Abstract: A fuel channel for housing a fuel rod bundle in a boiling water nuclear reactor includes an expanded section to create an increased flow area at a top of the fuel channel and thereby reduce a pressure drop through the fuel channel. The expanded section eliminates a need for channel spacers and a fastener guard.

Abstract: A ratio of the number of fuel assemblies loaded on a core to the number of control rod drive mechanisms is 3 or more. The fuel assembly itself contains mixed oxides of a low enrichment concentration uranium oxide containing 3 to 8 wt % in the average enrichment concentration of the fuel assembly, or mixed oxide containing not less than 2 wt %, but less than 6 wt % in the average enrichment concentration of fissile plutonium of. In the burner type BWR core on which the fuel assemblies are loaded, an average weight density of uranium, plutonium and minor actinides is 2.1 to 3.4 kg/L as a conversion at the value of unburned state.

Abstract: A fuel element for a nuclear reactor has fuel rods with nuclear fuel guided through spacers. The spacers are equipped with devices that exert a swirling impulse upon a coolant flowing along the fuel rods. In order to present as little flow resistance as possible for the coolant, these swirl-introducing devices have the form of a vane with a spoonlike or bladelike shape and they extend into the coolant flow. Owing to the shape—here the vane is curved in the longitudinal and in the transverse directions—practically all cross sections of the vane have such a high geometrical moment of inertia that even a vane made of a thin sheet metal is sufficiently rigid. Fuel elements configured according to the invention are particularly suitable for use in boiling water nuclear reactors.

Abstract: One object of the present invention is to provide a production method for a nuclear fuel assembly support grid that improves the corrosion resistance of welded parts without impairing the characteristics of the support grid so as to be able adequately withstand highly efficient operation. In order to achieve the object, the present invention provide a production method for a nuclear fuel assembly support grid comprising the steps of: assembling a plurality of straps in a grid form; welding intersections of each strap; and carrying out annealing thereafter to precipitate an intermetallic compound on the welded parts.

Abstract: Transverse vibrations of the pellet columns included in the fuel rods of fuel elements are limited by elastically mounting the fuel rod jacket tubes in the mesh of spacer grids. When the fuel rods are supported in this way, flexural vibrations of a higher order occur that lead to damage to the jacket tubes caused by fretting. These vibrations are the less dampened the more rigid the fixture of the fuel rod is. These vibration conditions are more easily excited and more strongly dampened when the pellet columns are more mobile, thereby removing vibration energy from the fuel element and avoiding damage caused by fretting. The mobility of the columns can be increased by increasing the gap between the pellet and the jacket tube, or by using constructions in which a torque M?10 N mm on the fuel rod leads to a tilting angle ??0.1°.

Abstract: A fuel assembly attains high burnup and increases reactor shut-down margin when loaded into a reactor core wherein a water gap width on a control rod side and a water gap width on a side opposite to the control rod side are almost equal to each other. The fuel assembly has a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets and also has at least one neutron moderator rod shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly.

Abstract: A spacer grid with hybrid flow-mixing devices for nuclear fuel bundle is made up of an intersection of a plurality of thin straps at right angles to form a plurality of cells for receiving and supporting fuel rods. Each strap is composed of two types of strap units, called a primary strap unit and a secondary strap unit, which are alternately arranged along the strap. The primary strap unit is a strap section having a primary vane set, and a secondary strap unit is a strap section having a secondary vane set. The straps intersect such that, by primary and secondary strap units, each intersection forms a hybrid flow-mixing device around the top of each junction. The primary vane set, consisting of a trapezoidal primary vane stand and two bent primary mixing vanes on both sides, protrudes upwardly from the strap and is primarily for generating cross flow between channels.

Abstract: A crud-resistant nuclear fuel element cladding in which the axial locations that experience nucleate boiling during reactor full power operation are highly polished so that the maximum size of any surface defect on the highly polished surface is approximately 0.1 microns. The remainder of the cladding surface remains unpolished so that crud is more evenly redistributed over the entire fuel cladding surface to limit the thickness of the crud that is formed to less than 35 microns.

Abstract: Separation devices are disposed in the vent volume above part-length rods and above one or more of the spacers above the upper ends of the part-length rods. The separation devices preferably comprise swirlers located above the lattice openings which would otherwise receive the rods but for the underlying part-length rods. In this manner, flow is directed laterally outwardly onto the surfaces and into the interstices of the full-length fuel rods for improved power performance while simultaneously adverse pressure drops across the spacers are minimized.

Abstract: A fuel assembly having a plurality of fuel rods arranged in a square lattice array. The fuel rods include a plurality of short-length fuel rods each having a fuel active length shorter than that of each of remaining ones of the fuel rods. At least one water rod is arranged in a region in which one or more of the fuel rods are arrangeable in the array, and a plurality of fuel spacers are provided at a plurality of positions in the axial direction for holding the plurality of fuel rods and the at least one water rod, with mutual radial intervals therebetween being kept immovable. The plurality of short-length fuel rods include at least one first short-length fuel rod arranged in the outermost peripheral region of the square lattice array. Each of the plurality of fuel spacers include a plurality of cylindrical members.

Abstract: A double strip mixing grid for nuclear reactor fuel assemblies is disclosed. This grid is fabricated by intersecting at right angles a plurality of double strips, each fabricated by welding two thin sheets together into a single structure with coolant channels. The mixing grid, having the channels, effectively mixes low temperature coolant with high temperature coolant within a fuel assembly, thus improving the thermal efficiency of the fuel assemblies. This mixing grid also effectively prevents the coolant from being partially overheated, thus improving the soundness of nuclear reactors. This mixing grid also has swirling flow blades and/or lateral flow blades to further improve the thermal efficiency of the fuel assembly. This mixing grid elastically supports the fuel rods by the sheets of the double strips, collaterally acting as positioning springs.

Abstract: A fuel assembly attains high burnup and increases reactor shut-down margin when loaded into a reactor core wherein a water gap width on a control rod side and a water gap width on a side opposite to the control rod side are almost equal to each other. The fuel assembly has a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets and also has at least one neutron moderator rod shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly.

Abstract: A reduced pressure drop debris filter bottom nozzle for use in a fuel assembly of a nuclear reactor includes a plate member formed with a plurality of first flow holes and a plurality of second flow holes. The first flow holes are oblong in cross section and may be of an oval configuration. The first flow holes each have in cross section a major axis and a minor axis, the major axis being longer than the minor axis. The second flow holes are circular in cross section and may have a diameter substantially equal to the minor axis of the first flow holes. The bottom nozzle also features support ligaments that extend between the first flow holes and that are axially aligned with fuel rods within the fuel assembly.

Abstract: In a boiling water fuel assembly, some of the fuel rods are shortened. It is necessary to establish a sufficiently high maximum power for transition to boiling. To optimize this power, spacers are at a constant distance at a bottom and are at a shorter distance at a top. The spacers belonging to upper group have turbulence-generating vanes which, however, do not project above the shortened fuel rods.

Abstract: A support grid for laterally maintaining the relative position of elongated fuel elements within a fuel assembly for use within a core of a nuclear reactor. The grid is formed in the shape of a lattice with the intersecting lattice members defining a plurality of cells, most of which respectively support the nuclear fuel elements. The remaining cells support nuclear control rod guide tubes and instrumentation thimbles. The cells supporting the nuclear fuel elements are provided with diagonally positioned springs on two, adjacent walls. The springs support the fuel elements against dimples which protrude from the opposite cell walls. The adjacent, diagonal springs in each fuel element cell are inclined in opposite directions. The walls of the cells supporting the control rod guide tubes are embossed along their height at the locations intermediate the intersection between adjoining walls with a concave notch having a curvature which conforms to the outside surface curvature of the control rod guide tubes.

Abstract: A spacer grid for PWR assemblies is characterized by curved flow channels between adjacent fuel rods and straight, essentially flat strips connecting opposite side plates of the spacer. The latter strips prevent bowing-out of the side plates during fuel assembly fabrication and during operation in the reactor. Additionally, the spacer grid allows accurate positioning of the fuel rods on a square lattice with a precisely defined pitch, and support of the rods in their spacer cells is such that rod bow will be minimized. The direction of the nozzles on the flow channels has been chosen to promote cross-flow of the coolant through the assembly.

Abstract: The invention relates to a fuel assembly for a boiling water reactor which is adapted, during operation of the reactor, to allow water to flow upwards through the fuel assembly while absorbing heat from a plurality of fuel rods, whereby part of the water is transformed into steam. The fuel assembly comprises a steam channel through which the steam flows through the fuel assembly. The steam channel (16a, 16b, 16c, 16d) consists of an empty volume which at least extends through part of the fuel assembly. The fuel assembly is designed such that the water and the steam are brought to rotate around the steam channel whereby the water is thrown away from the steam channel whereas the steam which is separated from the water flows upwards through the steam channel.

Abstract: A fuel assembly includes a plurality of fuel rods placed in a square lattice array of 9-rows/9-columns and at least one water rod. In this fuel assembly, the fuel rod pitch of the plurality of fuel rods is in a range of 14.15 mm to 14.65 mm, and means for offsetting and holding a fuel bundle composed of the fuel rods and the water rod is provided in such a manner that the center in a cross section of the fuel bundle is offset from the center in a cross section of the lower tie plate toward the channel fastener side. With this configuration, it is possible to provide a fuel assembly for a D-lattice core, which is capable of achieving the fuel economy comparable to that of a C-lattice core without reducing the thermal margin, and of using the existing fuel spacers.

Abstract: A fuel bundle assembly for a boiling water nuclear reactor comprising a plurality of fuel rods having respective fuel columns therein, and arranged in an ordered array, extending between upper and lower support structures, the plurality of fuel rods enclosed within a hollow, open-ended channel member at least partially enclosed by the open-ended channel member; at least one water rod supported on the lower tie plate and extending upwardly toward the upper tie plate, the at least one water rod having an upward flow path including at least one inlet at a lower end of the upward flow path, and a downward flow path including at least one outlet at a lower end of the downward flow path, the at least one outlet located about midway along the fuel columns within the fuel rods.

Abstract: A fuel assembly attains high burnup and increases reactor shut-down margin when loaded into a reactor core wherein a water gap width on a control rod side and a water gap width on a side opposite to the control rod side are almost equal to each other. The fuel assembly has a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets and also has at least one neutron moderator rod shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly.

Abstract: A nuclear fuel spacer grid, fabricated by intersecting a plurality of zircaloy or inconel grid strips and used for placing and supporting a plurality of elongated fuel rods within a nuclear fuel assembly, is disclosed. In the spacer grid of this invention, each of the grid strips is not cut away to form separate springs or dimples for supporting the fuel rods, but has an axial slot extending from one end of each strip to a length. The grid strips are intersected at the slots prior to being welded together into a single grid structure at a welding tap formed at an outside end or a middle portion of each of the slots. Each of the grid strips also has a dipper-shaped coolant mixing vane, or a dipper vane, at each of the upper and lower ends thereof. The spacer grid thus maximizes the thermal hydraulic coolant mixing effect within a fuel assembly and stably supports the fuel rods within the assembly while improving the mechanical/structural strength of the assembly, such as a buckling strength.

Abstract: The invention concerns a spacer (14) for a nuclear boiling water reactor. The spacer (14) comprises a plurality of cells (16) for holding or allowing elongated elements (12) to pass through the cells. Between the cells (16) there are a plurality of flow channels (18). The spacer comprises at least a plurality of deflecting members (22). The deflecting member comprises a vane (24) which extends in a direction from a cell (16) into the neighbouring flow channel (18). The vane is inclined relative to a vertical plane (26) and is wider in its upper part than in its lower part. The invention also concerns a fuel assembly for a nuclear boiling water reactor, comprising a deflecting member with vane of similar construction.

Abstract: A fuel assembly, particularly, a fuel assembly including short-length fuel rods and fuel spacers, is used for a boiling water reactor, which is capable of sufficiently reducing the pressure loss of at least one of the fuel spacers positioned above the upper ends of the short-length fuel rods, irrespective of the arrangement of the short-length fuel rods, and also ensuring the structural strength of the fuel spacer. The fuel assembly includes fuel rods located in a square lattice array, two water rods arranged in a region in which seven of the fuel rods are arrangeable, two fuel spacers for holding the fuel rods and the water rods with mutual intervals kept immovable. Each of the fuel spacers includes cells which are connected to each other and in which the fuel rods are to be inserted, respectively, and a band for surrounding the outermost peripheries of the cells. The short-length fuel rods include four first short-length fuel rods arranged in the outermost peripheral region of the square lattice array.

Abstract: A fuel assembly for a boiling water reactor comprising full-length fuel rods (3a, 3c) with a first length extending over the height of the entire fuel assembly, and part-length fuel rods (3b) with a second length extending only in the lower part (10) of the fuel assembly, the fuel rods which have positions immediately adjacent to the part-length fuel rods being adapted so as to be bent inwards, in their upper part, towards the open region (15) which is formed above the part-length fuel rods. At least half of the fuel rods in the fuel assembly are straight.

Abstract: In each of a number of fuel assemblies loaded in a core of a boiling water reactor, a fuel holding portion of a lower tie plate holds lower end portions a plurality of fuel rods and at least one water rod. The water rod includes a rising pipe opened to a space in the lower tie plate below the fuel holding portion and introducing upward a coolant introduced to the rising pipe, and a falling pipe communicated with the rising pipe and introducing downward the coolant introduced through the rising pipe. The falling pipe has a coolant outlet opened to a second coolant passage defined between the fuel rods above the fuel holding portion. The rising passage is filled with the coolant during a period of rated power operation of the reactor, and a surface of the coolant is formed in the rising pipe during a period of non-rated power operation in which a flow rate of the coolant supplied to the fuel assemblies is lower than that during the period of rated power operation.

Abstract: A fuel assembly for a nuclear reactor is described, the fuel assembly including: a plurality of fuel pins (12) extending substantially parallel to the axis of the assembly and to each other; at least two structural grids spaced apart from each other, the grids being in contact with said fuel pins (12) and maintaining said fuel pins substantially mutually parallel and preventing contact therebetween, wherein the fuel assembly further comprises at least one mixing grid (50) situated intermediate said at least two structural grids, the fuel assembly being characterized in that said mixing grid (50) is positioned and fixedly located out of substantial contact with said fuel pins (12), the mixing grid also having turbulence inducing means (61) to promote turbulence in a coolant (62) flowing through said fuel assembly in use and in that the mixing grid is formed from sheet metal wherein the plane of the metal sheet from which the mixing grid is formed lies in a plane which is transverse to the axis of the fuel pin

Abstract: A fuel assembly for a boiling water reactor comprising at least one rotary cell (13a-13d) which has fuel rods (4) arranged in a number of concentric rings with a substantially circular shape, and a steam conducting channel (17a-17d) arranged in the centre of the concentric rings through which steam flows upwards through the fuel assembly. At least certain of the fuel rods in the rings are arranged such that their upper ends are displaced in relation to their lower ends in the tangential direction such that water and steam are brought to rotate around the steam conducting channel.

Abstract: The present invention relates to a fuel assembly for a light-water nuclear reactor with a substantially square cross section which comprises fuel rods (4) extending between a bottom tie plate (16) and a top tie plate (17). A coolant is adapted, during operation, to flow upwards through the fuel assembly. According to one aspect of the invention, the fuel assembly comprises a plurality of fuel units (3) stacked on top of each other, wherein each fuel unit (3) comprises a plurality of fuel rods (4) extending between a top tie plate (17) and a bottom tie plate (16). The fuel units are arranged attached to a support structure (4a, 14, 14a, 14b) extending through the whole fuel assembly such that axial gaps are formed between the fuel units (3). One of the tie plates is freely movable relative to the support structure.

Abstract: A nuclear fuel bundle has differential peak power limits for the edge or peripheral fuel rods and the interior fuel rods. Also, the magnitude of nuclear fuel in the edge or peripheral rods is decreased in comparison with the magnitude of nuclear fuel in the interior rods. The nuclear reactor can thus operate at higher power output by decreasing the margins between the power outputs and peak power limit of the interior rods, as well as by decreasing the margins between the power outputs of the edge or peripheral rods and the increased peak power limit of those rods. The outer or peripheral edge rods can also be enriched for enhanced power output.

Abstract: A fuel bundle assembly for a boiling water nuclear reactor comprising a plurality of fuel rods having respective fuel columns therein, and arranged in an ordered array, extending between upper and lower support structures, the plurality of fuel rods enclosed within a hollow, open-ended channel member at least partially enclosed by the open-ended channel member; at least one water rod supported on the lower tie plate and extending upwardly toward the upper tie plate, the at least one water rod having an upward flow path including at least one inlet at a lower end of the upward flow path, and a downward flow path including at least one outlet at a lower end of the downward flow path, the at least one outlet located about midway along the fuel columns within the fuel rods.

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 support rod 14 carrying one or more separation devices 12, e.g., swirlers, is releasably secured in a fuel bundle. The support rod and separation devices are sized to pass through openings in the spacers S otherwise containing full length fuel rods. The lower end of the support rod is releasably connected to the upper end of a part-length fuel rod PLR which in turn is releasably connected to the lower tie plate. The support rod, separation devices and part-length rod may be installed and removed relative to the fuel bundle as an integral assembly with the part-length rod and separation devices passing through the openings in the spacers. When installed, the separation devices lie above upper spacers in the vent volumes to flow liquid on and into the interstices of the surrounding fuel rods.

Abstract: In a reactor core, there is charged a number of fuel assemblies composed of a channel box and a fuel bundle disposed therein, in which fuel rods adjacent to each other are arranged so as to provide a triangular shape and a ratio of a coolant channel cross section to a fuel cross section is set to be 1 or less.

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).