Abstract: An improved retention system for retaining fuel rods in a fuel assembly is disclosed. The retention system includes a plurality of first engagement surfaces on the bottom nozzle of a fuel assembly. There is at least one engagement surface for each fuel rod. A second engagement surface is formed on the bottom end plug of each fuel rod. The first and second engagement surfaces are configured for engagement with each other for axially and laterally retaining each fuel rod within the fuel assembly. Debris deflectors may also be provided to deflect debris from coolant channels surrounding the fuel rods.

Abstract: An improved retention and alignment system for nuclear fuel rods includes an upper nozzle plate and a lower nozzle plate, nuclear fuel rods, each having an upper end and a lower end and extending axially between the upper and lower nozzle plates, a first precision magnet incorporated onto the lower end of the fuel rod, and a plurality of second precision magnets incorporated onto the lower nozzle plate in positions confronting the first precision magnets on the fuel rods. Each first precision magnet has at least one of a magnetic north or south polarity and the second precision magnet has at least one of a magnetic south or north polarity opposite the polarity of the confronting first precision magnet to effect magnetic attraction between the confronting first and second precision magnets. Grids between the upper and lower nozzle plates form cells through which the fuel rods pass.

Abstract: A fuel assembly for a boiling water reactor having fuel rods, two or three water rods, a tie plate, spacers, a handle, and a joint arrangement. The joint arrangement is configured to transfer a vertical lifting force from the handle to the water rods. The joint arrangement includes a balancing element arranged between the water rods and the handle. The joint arrangement includes a first joint arranged between the balancing element and the handle and a set of second joints arranged between a respective one of said water rods and said balancing element. The first joint and the set of second joints are configured to allow a rotational movement of said balancing element in relation to said handle as well as in relation to said water rods in order to balance lifting forces in the water rods.

Abstract: An improved retention system for retaining fuel rods in a fuel assembly is disclosed. The retention system includes a plurality of first engagement surfaces on the bottom nozzle of a fuel assembly. There is at least one engagement surface for each fuel rod. A second engagement surface is formed on the bottom end plug of each fuel rod. The first and second engagement surfaces are configured for engagement with each other for axially and laterally retaining each fuel rod within the fuel assembly. Debris deflectors may also be provided to deflect debris from coolant channels surrounding the fuel rods.

Abstract: A lower nozzle for use in a nuclear fuel assembly provided. The lower nozzle is of the type having an axis and comprising a transverse lower tie plate for channeling the coolant through the lower tie plate and a tubular skirt extending axially from the periphery of the lower tie plate, the skirt delimiting an axial housing closed at one end by the lower tie plate and open at the opposite end, a debris filter configured for axial insertion in the housing and snap-fit springs for retaining the debris filter in the housing after insertion. The springs are configured to shift the debris filter axially towards the lower tie plate.

Abstract: A fuel bundle for a nuclear reactor core is provided. The fuel bundle may include a plurality of rods comprised of nuclear fuel rods and/or isotope production rods. Each rod includes a plurality of interconnected rod segments, wherein at least two of the rod segments of at least one rod have different outside diameters. The fuel bundle may additionally include a plurality of rod spacer grids securely retained between axially adjacent, interconnected rod segments. The rod spacer grids interconnected between axially adjacent rod segments form an array of substantially equally spaced rods. The fuel bundle may further include an elongate tubular channel in which the arrayed rods are housed.

Abstract: A fuel assembly may include a channel nosepiece; a lower tie plate positioned above the channel nosepiece; and at least one bundle retention clip connected to the channel nosepiece and the lower tie plate and configured to resist movement of the lower tie plate away from the channel nosepiece.

Abstract: A nuclear fuel assembly tie plate is provided. The nuclear fuel assembly tie plate is formed by intersecting strips delimiting between them tubular guide cells each for allowing a fuel rod to extend through the tie plate. The strips delimit between them tubular flow cells separate from the guide cells, each flow cell for allowing coolant flow through the tie plate. Guide cells and flow cells are arranged at nodes of a lattice defined by a repeating pattern comprising four corner nodes in a square lattice arrangement and a central node at the center of the four corner nodes, with one guide cell at each corner nodes, separated by a pair of parallel spaced strips intersecting a pair of parallel spaced strips, the two pairs of strips delimiting a four-walled central flow cell at the center node.

Abstract: Example embodiments are directed to tiered tie plates and fuel bundles that use tiered tie plates. Example embodiment tie plates may include upper and lower tiered tie plates. Example embodiment tiered tie plates may have a plurality of bosses divided into groups, or tiers, having differing vertical (axial) displacement. Example embodiment fuel bundles may use tiered tie plates such that fuel rods in example bundles may originate and terminate at different vertical displacements, based upon the vertical displacement of the bosses receiving the fuel rods into the tiered tie plates. Optionally, shanks may be used to further vary fuel rod axial displacement and diameter.

Abstract: Example embodiments are directed to tie plate attachments having irradiation targets and/or fuel assemblies having example embodiment tie plate attachments with irradiation targets and methods of using the same to generate radioisotopes. Example embodiment tie plate attachments may include a plurality of retention bores that permit irradiation targets to be contained in the retention bores. Irradiation targets may be irradiated in an operating nuclear core including the fuel assemblies, generating radioisotopes that may be harvested from the spent nuclear fuel assembly by removing example embodiment tie plate attachments.

Abstract: A nuclear reactor has a core installed on a lower core plate and formed from multiple fuel assemblies, each fuel assembly including a structural cage assembly. The structural cage assembly has an upper end fitting, mid grids, and a lower end fitting (LEF). The LEF positions the fuel assembly using four locating pins located at each corner of the LEF. The pins position the fuel assembly laterally by mating with receiving holes in the lower core plate. The locating pins have a chamfered tip with a flat end. The chamfered tip allows for a greater positioning margin when installing the fuel assembly in the core by guiding the pins into holes in the lower core plate, and the flat tip provides strength and stability in case the assembly is inadvertently rested on the tip of the pin instead of the LEF pads.

Abstract: A fuel assembly including a plurality of fuel rods arranged mutually in parallel wherein the fuel rods include a fissile material, a plurality of guide tubes arranged in parallel with and interspersed amongst the fuel rods, an upper end fitting connected with upper ends of the guide tubes, and a lower end fitting connected with lower ends of the guide tubes. At least one of the upper end fitting and the lower end fitting includes a grid formed by interlocking metal strips secured together at intersections between the metal strips.

Abstract: In a nuclear reactor core having fuel assemblies with upper and lower end fittings, a debris filter plate is attached to a lower end fitting having a skirt. The filter prevents debris from entering the fuel assembly, while the skirt prevents the trapped debris from sliding off the lower end fitting and continuing into the core. The lower end fitting is formed from a substantially square base and has flow channels to allow coolant to flow through it to the fuel assembly. The skirt is an extension of the metal of the lower end fitting that extends around the perimeter of the lower end fitting, spanning all four corners of the lower end fitting. In addition to capturing debris, the skirt also positions the filter, which may be manufactured from the same metal as the lower end fitting.

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: Example embodiments are directed to tiered tie plates and fuel bundles that use tiered tie plates. Example embodiment tie plates may include upper and lower tiered tie plates. Example embodiment tiered tie plates may have a plurality of bosses divided into groups, or tiers, having differing vertical (axial) displacement. Example embodiment fuel bundles may use tiered tie plates such that fuel rods in example bundles may originate and terminate at different vertical displacements, based upon the vertical displacement of the bosses receiving the fuel rods into the tiered tie plates. Optionally, shanks may be used to further vary fuel rod axial displacement and diameter.

Abstract: Example embodiments are directed to tiered tie plates and fuel bundles that use tiered tie plates. Example embodiment tie plates may include upper and lower tiered tie plates. Example embodiment tiered tie plates may have a plurality of bosses divided into groups, or tiers, having differing vertical (axial) displacement. Example embodiment fuel bundles may use tiered tie plates such that fuel rods in example bundles may originate and terminate at different vertical displacements, based upon the vertical displacement of the bosses receiving the fuel rods into the tiered tie plates. Optionally, shanks may be used to further vary fuel rod axial displacement and diameter.

Abstract: A filter including a plurality of flow ducts extending in a longitudinal direction and each delimited between one pair of walls. According to one aspect of the invention, the filter includes deflectors protruding into each duct alternately from the pair of walls with overlapping in the longitudinal direction to define a zigzag shaped flow channel and provided with at least one set of holes aligned in the longitudinal direction to define through the overlapping deflectors a passage for accommodating a lower end pin of a fuel rod.

Abstract: A fuel assembly is charged in a reactor core of a nuclear reactor using a liquid metal as a coolant, and includes a wrapper tube storing a plurality of fuel pins and including an entrance nozzle for introducing the coolant and an operation handling head, grids disposed in the wrapper tube to support the fuel pins in the radial direction of the wrapper tube, liner tubes inserted in the wrapper tube to fixedly hold the respective grids in the axial direction of the wrapper tube, and a fixing device for fixing the grids and the liner tubes in the radial direction of the wrapper tube.

Abstract: A fuel assembly for a boiling-water reactor has a water channel and a fuel assembly base, made from a sieve plate and a frame section enclosing the same. The water channel supports a plug with a bore running therethrough, at the lower end thereof, to which the fuel assembly base is fixed. The fuel assembly further comprises an opening through the sieve plate, a skirt, formed on the underside of the plug, surrounding the bore, extending into the opening in the sieve plate, a bush, provided with a first and a second longitudinal section, whereby the first longitudinal section extends from the underside of the sieve plate into the opening in a rotationally-fixed manner and a radial shoulder is provided between the two sections which contacts the underside of the sieve plate. A threaded section of a screw extends through the bush which engages in a thread in the bore in the plug.

Abstract: Example embodiments are directed to tie plate attachments having irradiation targets and/or fuel assemblies having example embodiment tie plate attachments with irradiation targets and methods of using the same to generate radioisotopes. Example embodiment tie plate attachments may include a plurality of retention bores that permit irradiation targets to be contained in the retention bores. Irradiation targets may be irradiated in an operating nuclear core including the fuel assemblies, generating radioisotopes that may be harvested from the spent nuclear fuel assembly by removing example embodiment tie plate attachments.

Abstract: Example embodiments are directed to tie plate attachments having irradiation targets and/or fuel assemblies having example embodiment tie plate attachments with irradiation targets and methods of using the same to generate radioisotopes. Example embodiment tie plate attachments may include a plurality of retention bores that permit irradiation targets to be contained in the retention bores. Irradiation targets may be irradiated in an operating nuclear core including the fuel assemblies, generating radioisotopes that may be harvested from the spent nuclear fuel assembly by removing example embodiment tie plate attachments.

Abstract: An assembly of the type having a water channel extending along a longitudinal axis and having an upper section of larger cross-section area than a lower section and at least one fuel rod receiving groove extending longitudinally on the outer surface of the lower section, fuel rods extending longitudinally and disposed around the water channel and fixing members for fixing at least one fuel rod to the water channel in the at least one groove below the upper section. According to one aspect of the invention, the at least one groove extends along the upper section such that a fuel rod received in fixing members is longitudinally extractable or insertable from the upper end side of the fuel assembly.

Abstract: A lower and upper end plugs of an annular fuel rod, into and out of which cooling water flows, comprises: a lower end plug including a filter for debris which has a plurality of pins intersecting each other at the proper position of an inner channel main inlet, through-holes into which the pins of the debris filter are fitted, and at least one inner channel auxiliary inlet through which the cooling water flows into a lower inner channel thereof when the inner channel main inlet is blocked by debris, and which has a through-hole shape; and an upper end plug including at least one upper handling groove and hole, into which a fuel rod handling tool is coupled, at a proper position of an inner circumference of the inner channel main outlet in a circumferential direction.

Abstract: Example embodiments are directed to fuel assembly components and nuclear fuel bundles including the fuel assembly components. Example embodiments of a fuel assembly component may include a cylindrical device having first and second ends and a mounting assembly on the first end of the cylindrical device configured to attach to and detach from a partial length fuel rod. Example embodiments of a nuclear fuel bundle may include an upper tie plate, a lower tie plate, at least one full-length fuel rod, at least one partial length fuel rod, and a fuel assembly component.

Abstract: A resilient bush for frictionally engaging a centering pin of the fuel assembly is fixed in each of the through-holes of at least one of the end-pieces of the fuel assembly. The resilient bush comprises an annular member which has a portion for fixing in the hole of the end-piece and resilient arms which are separated by apertures. The flexible arms of the resilient bush comprise, in a free end portion, a supporting surface which projects radially inside the bush whose diameter is smaller than the diameter of a centering pin of the fuel assembly.

Abstract: In a fuel assembly for a nuclear reactor, a plurality of nuclear fuel rods and at least one fuel rod spacer assembly supporting the fuel rods in an organized array. The fuel rod spacer assembly includes a guide at a leading edge of the fuel rod spacer assembly. The guide is angled towards the fuel rod for directing debris to open passages in the fuel rod spacer assembly.

Abstract: A secure connection between the bottom nozzle of a nuclear fuel assembly and the control rod guide thimbles having two or four crimped pockets in the side wall of a bottom nozzle leg counterbore which are formed by drilling two or four blind holes through the top surface of the bottom nozzle. After attaching the bottom nozzle to the fuel assembly with a crimp bolt a pneumatic tool is then inserted into a flanged cup feature on the crimp bolt head and the flanged portion of the cup feature of the crimp bolt is deformed into the crimp pockets. The crimp pockets are contained within the leg counterbore and prevent the screw from rotating or falling out of the assembly in the event of preload loss or screw fracture.

Abstract: A core plate assembly for a nuclear reactor includes a plurality of support beams, a flat plate positioned on top of the support beams, a plurality of control rod guide tube openings arranged in staggered rows, and a plurality of fuel supports extending through the flat plate. Each guide tube opening has a cruciform shape defines four fuel bundle receiving areas. Each fuel support includes a coolant flow inlet, and a coolant flow outlet sized to receive a lower tie plate of a fuel bundle. The coolant flow inlet is offset from coolant flow outlet so that a centerline of the coolant flow inlet is parallel to a centerline of the coolant flow outlet. The coolant flow inlets are positioned adjacent a support beam, and the coolant flow outlets are positioned in a fuel bundle receiving area.

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: 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 fuel assembly for a boiling water reactor comprising a plurality of fuel units, stacked on top of each other, each of which comprising a plurality of fuel rods extending vertically between a top tie plate and a bottom tie plate, and means for keeping the fuel elements together. The fuel elements are surrounded by a fuel channel with a substantially square cross section. At least two of the fuel units differ from each other in regard to fuel distribution or free flow area.

Abstract: The present invention relates to a fuel assembly (1) and a method therefor. The fuel assembly is intended for a light-water cooled nuclear reactor and comprises a first and a second locking member (9a, 9b, 10), a plurality of elongated elements (3, 3a) wherein each of the lower ends of the elongated elements is provided with an end plug (3b). The end plug (3b) is arranged guided or locked in an end plate (6) which comprises at least two adjacently disposed plug holes (6b) for receiving one end plug (3b) each. The first locking member (9a, 9b) is made in an end plug (3b) and has a concave shape and the second locking member (10) is arranged slidable in a locking hole (6c) which is adapted to extend between the two adjacently disposed plug holes (6b) and opening out into these. The second locking member (10) is made with a length exceeding the length of the locking hole (6c) and has end surfaces with shapes intended for cooperation with the concave surface of the first locking member (9a, 9b).

Abstract: A water rod for a fuel assembly of a boiling water nuclear reactor has a first end and a second end, wherein at least one of the first and second ends is directly attachable to a tie plate of the fuel assembly without an end plug. The structure of the present invention simplifies the manufacturing process and reduces the cost of the fuel assembly in the boiling water nuclear reactor. The water rod according to the invention has one or both of its ends configured to be directly attachable to the tie plate of the fuel assembly.

Abstract: The adaptor plate of a top nozzle assembly is removably secured to selected thimble tubes in a nuclear fuel assembly by quick release couplings. The openings in the adaptor plate aligned with the selected thimble tubes are counterbored from above to form shoulders with diametrically opposed slots extending downward through the shoulders. The quick release couplings include a sleeve secured to the upper end of the thimble tube. A support plate fixed to the sleeve has a pair of upwardly extending bosses engaging the slots in the adaptor plate. A latch member with a pair of diametrically opposed outwardly projecting latch ears rotates on the sleeve between a first position in which the latch ears are aligned with the slots and are positioned over the bosses so that the adaptor plate may be lifted off, and a second position with the latch ears overlaying the shoulder to latch the adaptor plate to the thimble tube.

Abstract: The present invention relates to a fuel assembly in or for a boiling water reactor, comprising a plurality of vertical fuel rods extending between a top and a bottom tie plate and surrounded by a sleeve-formed casing where the fuel rods are positioned with the aid of a plurality of axially separated spacers. The invention is characterized in that only one fuel rod is detachably arranged in the top tie plate and in the bottom tie plate and in that at least one of the other fuel rods is fixed to the bottom tie plate and adapted to extend above the top tie plate to obtain a tensile-force-transmitting connection with the bottom tie plate.

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 fuel bundle for a nuclear reactor includes a plurality of fuel rods extending between upper and lower tie plates, and a filter plate seated on the lower tie plate. The filter plate includes a substantially planar plate having a plurality of fuel rod holes in a predetermined array, the plate having web areas between the fuel rod holes which are formed with a plurality of smaller debris filter holes. At least one of the web areas is formed to include a spring tab pivotable out of the plane of the plate so that in the event of debris overload, coolant can bypass the smaller debris filter holes.

Abstract: In a fuel bundle assembly for a nuclear reactor wherein a plurality of fuel rods and tie rods extend between upper and lower tie plates and wherein some of the fuel rods are partial length fuel rods extending between the lower tie plate and a spacer located between the upper and lower tie plates, an improved end plug is provided for at least each of the partial length fuel rods, each end plug secured between a respective partial length fuel rod and the lower tie plate. The end plug includes an upper portion constructed of a first alloy material and including an exterior fuel rod receiving surface and a tapped hole in a lower end thereof, and a lower portion constructed of a second alloy material and including upper and lower threaded sections, the upper threaded section receivable within the tapped hole and the lower threaded section receivable within a tapped hole in the lower tie plate. The threaded end plug may be used with full length fuel rods as well as bundle tie rods.

Abstract: A nuclear fuel assembly for a pressurized water reactor having lower and upper tie plates, guide tubes, spacer grids, an instrumentation tube, and extended fuel rods which extend to the lower tie plate and which are spaced radially and supported along the guide tubes by the spacer grids, at least one of the extended fuel rods having at a lower end a fuel rod lower end cap secured by a first spring within an aperture in the lower tie plate and which exerts a lateral force against the lower end cap. The upper tie plate further includes a fuel rod support housing which extends down over the upper end of the at least one of the extended fuel rods and has a second spring positioned in a bore in the fuel rod support housing which exerts a lateral force on the upper end of the extended fuel rod positioned within the bore in the fuel rod support housing.

Abstract: A debris resistant fuel rod sleeve that is received over the lower end of a fuel rod. The sleeve extends above the top of the lowermost spacer grid. Openings are spaced apart around the circumference of the sleeve to correspond to the location of hard stops in the spacer grid. The hard stops are received in the openings and retain the sleeves in position during operation and during reconstitution or recaging if necessary. The outboard side of the peripheral sleeves may be provided with top and bottom lead-in features to prevent hang-ups.

Abstract: A fuel bundle assembly for a boiling water nuclear reactor includes an open ended tubular channel subdivided into four quadrants by at least two interior partitions, each quadrant having a sub-fuel bundle assembly having a plurality of fuel rods extending between upper and lower tie plates. An inter-bundle support plate receives a lower end of the channel and has four flow openings at an upper end thereof, such that the lower tie plate of each sub-fuel bundle supported in a respective one of the openings in the support plate. In one embodiment, the sub-fuel bundles within a channel are separated by a cruciform shaped coolant passage. In a second embodiment, the cruciform coolant passage is omitted to thus provide a homogeneous sub-fuel bundle configuration.

Abstract: The lower tie plate grid includes cylindrical bosses and webs interconnecting the bosses for supporting nuclear fuel rods and defining flow openings through the grid. Coolant flows through the flow openings for flow upwardly about the fuel rods. The grid includes upper and lower portions and a screen is disposed between the upper and lower grid portions upon assembly with the bosses and webs of the respective upper and lower grid portions in registry with one another. The grid portions are welded to one another whereby the apertured screen serves to separate debris from the coolant flowing through the flow openings. The screen has openings in registry with the openings defined by the bosses for receiving the end plugs of the fuel rods.

Abstract: A nuclear fuel assembly debris filter. Each fuel rod has a ring attached to the lower end cap. The rings are shaped and sized to define a space between the lower end cap and ring such that the space serves to trap, or filter, debris before it reaches the elevation of the fuel cladding. The rings may be circular, elliptical, or any suitable shape that provides the desired filtration effect.

Abstract: A boiling water reactor fuel assembly having a lowered fuel rod support plate and increased fuel rod length while restraining the fuel rods against lateral vibration.

Abstract: A fuel assembly (16) for a boiling-water nuclear reactor arranged in groups with four fuel assemblies in each group and with a centrally placed control rod (17) forming a supercell. Each fuel assembly (16) includes a plurality of vertical fuel rods (12) with enriched nuclear fuel material (24), said rods being arranged between a bottom tie plate (13) and a top tie plate (14) in a surrounding vertical fuel channel (1) which is connected to a transition section (2). The transition section is provided with holes (20a-d) for by-pass flow outside the fuel assembly. The fuel assembly is characterized in that the by-pass holes are arranged in such a way that when turning the fuel assembly (16), including the transition section (2), 90.degree., 180.degree. or 270.degree. around the longitudinal axis of the fuel assembly, said holes are adapted to direct the by-pass flow away from the control rod (17).

Abstract: A unitary one-piece lower tie plate grid has a lower portion and an upper portion for supporting the fuel rods. The lower tie plate grid includes cylindrical boss portions arranged in square matrices for receiving the lower end plugs of the fuel rods. Web portions interconnect the boss portions along the sides of the matrices. The lower grid portion includes a plurality of openings which open into the flow spaces defined by the convex portions of the bosses and the webs within each square matrix of the upper portion of the tie plate. Coolant flows through the lower flow openings into the flow spaces for further flow upwardly about the fuel rods. The openings are defined by the convex lower portions of the bosses and webs, as well as projections which extend laterally inwardly from the convex surfaces of the lower boss portions toward a central region in the middle of the square matrix.

Abstract: A fuel assembly supporting structure for a nuclear reactor fuel assembly which comprises a two-way shape-memory alloy. A shape-memory alloy is selected which has an overall transition temperature range substantially above atmospheric temperature and substantially below a temperature experienced by the shape-memory alloy under reactor operating conditions. By using a shape-memory alloy in the design, the support structure assumes a first configuration for securely supporting one or a plurality of nuclear reactor components at a temperature above the overall transition temperature range and assumes a second configuration for loosely engaging the reactor components below the transition temperature range.

Abstract: A gap between a foot part and a channel of a boiling water fuel assembly is sealed against a coolant flow by a spring being supported by a central part thereof against the channel and by sides thereof against the foot part and being clipped and/or clamped on at that location even when all of the fuel rods are removed. For this purpose, the upper edge can extend around the foot part edge or the spring may be constructed as a spring band running entirely around the foot part and being fitted into a lateral groove.

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 comprises a plurality of fuel rods which contain nuclear fuel material inside, a lower tie plate which holds the lower end of the fuel rods and has a path inside to lead coolant between the fuel rods, and a channel box which encloses a bundle of the fuel rods. An orifice, in which a plurality of round rods are arranged to cross the coolant flow path, is installed in a through hole at a side wall of the lower tie plate by connecting to the side wall. Orifice coefficient of the orifice becomes large at small flow rate of coolant which supplied to the fuel assembly, and becomes small at large flow rate of coolant. By using the fuel assembly described above, void fraction in a gap region between fuel assemblies can be altered during beginning and end of an operation cycle of the nuclear reactor.