Abstract: An improved lower end fitting (L.E.F.) having a bell mouth type of flow jet diffuser decrease pressure drop 10-15%, more evenly distributes flow and adds strength. It includes neutron thimble flux impingement shield of instrument and/or cable. Diffusers are stainless steel of circular cross-sect. and parabolic to optimize diffusion. Shape is based on lower core plate flow hole geometry, L.E.F. design and reactor flow rate. Thinner L.E.F. legs, smaller L.E.F. gussets and thinner L.E.F. flow plates possible.

Abstract: A fuel assembly comprises a plurality of fuel rods, a lower tie plate for supporting lower ends of the fuel rods, and a channel box surrounding a bundle of the fuel rods and the circumference of the lower tie plate to thereby define a cooling water leak passage between the lower tie plate and the channel box. The fuel assembly includes a venturi provided in the lower tie plate for generating a force tending to attract the channel box toward the lower tie plate under the action of a leak stream of the cooling water passing through the cooling water leak passage. The fuel assembly also includes an arrangement provided in the lower tie plate for suppressing vibrations of the channel box caused upon an influence of the venturi.

Abstract: A fuel assembly for a boiling water reactor includes an elongated fuel assembly case, mutually parallel fuel rods having longitudinal axes and being disposed in the case, and longitudinally extending inner walls having lateral surfaces facing toward the fuel rods. At least some of the lateral surfaces have grooves formed therein extending perpendicular to the longitudinal axes of the fuel rods. A boiling water reactor includes a boiling water circuit having a pressure vessel and a steam turbine. A plurality of the fuel assemblies are disposed mutually parallel in the pressure vessel. The fuel rods are bathed by boiling water flowing around them in the longitudinal direction of the fuel rods.

Abstract: In a fuel assembly having fuel rods inserted into regularly arranged cells of a fuel spacer which keeps the fuel rods correctly spaced from one another and has spacer elements disposed in a plurality of stages in the longitudinal direction of the fuel rods, the fuel spacer comprises vanes formed on the cells in such a manner that each vane is bent from a cut formed in a part of the side wall of the cell. The vanes obliquely project into the corresponding spaces between adjacent fuel rods and allow a coolant flowing through the spaces and forming two-phase flows to generate swirling flows toward the fuel rods. The fuel spacer may alternatively comprise either thin-walled cylinders having built-in vanes or spiral vanes, which are fixed to the spacer that has not been subjected to any direct machining. Also disclosed is a fuel assembly provided with any of the above-described fuel spacers.

Abstract: A method and apparatus for assembling an egg-crate type grid (10) by orthogonally interengaging slots (30,32) cut transversely into one longitudinal edge of each of a plurality of metal strips (12,14). A first plurality of strips (14) is supported on their lower unslotted edges in north-south orientation so that the strips are uniformly spaced apart in parallel in the east-west direction with all the slots (32) oriented upwardly on the upper edge. The slotted upper edges (26) of adjacent north-south strips are then spread farther apart in the east west direction while maintaining the lower edges (28) at said uniform spacing. The lower, slotted edges (24) of a second plurality of east-west oriented strips are interengaged with the north-south strips while the selected portions of the upper edges of the north-south strips are spread. The upper edges of the first plurality of strips are then returned to the unspread orientation.

Abstract: A nuclear fuel assembly has a plurality of fuel rods and a lower tie plate supporting their lower ends. Coolant apertures extending through the lower tie plate. A channel box surrounds the fuel rods and receives the lower tie plate, to confine the coolant. To restrict leakage of coolant between the tie plate and the channel box, the coolant apertures include, adjacent the periphery of the lower tie plate, a plurality of peripheral apertures which are located at least partly outside the outermost fuel rods. The peripheral apertures each provide a coolant velocity peak located further from the axial center line of the tie plate than the axial center lines of the closest neighboring fuel rods. The invention also provides venturis in the leakage path between the channel box and the tie plate, to restrict deformation of the tie plate.

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: A nuclear fuel assembly with a debris filter. The lower end fitting of the fuel assembly has a stamped plate attached thereto that serves as a debris filter immediately upstream of the fuel rods. The stamped plate is provided with a plurality of flow holes in a size and pattern that provides filtration of debris damaging to the fuel rods while maintaining adequate coolant flow through the fuel assembly.

Abstract: In a fuel bundle for a boiling water reactor having one or more part length rods in the two phase region, a steam vent tube is introduced overlying the part length rods. The fuel bundle includes a lower tie plate for admitting water moderator and supporting a plurality of fuel rods in upstanding side-by-side relation, an upper tie plate for permitting water and steam to be discharged from the top of the fuel bundle and maintaining the fuel rods in upstanding side-by-side relation, a surrounding fuel channel for confining moderator flow along a path over the fuel rods and between the tie plates, and dispersed vertically intermittent spacers for maintaining the fuel rods in their designed side by side relation. One or more fuel rods extends from the lower tie plate vertically less than the full length to the upper tie plate ending interior of the fuel bundle at a disposition where the upper end of the part length rods is braced in the vertical position by a spacer.

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: A grid spacer for a nuclear reactor fuel assembly is formed of two superposed combs. Each comb has a base strip which extends the width of the assembly. To it are attached parallel grid strips which are free at their other ends. The grid strips are perpendicular to the base strip and are formed for spring engagement with the fuel rods of the assembly. The combs can be inserted from the sides of the assembly, so that an additional or substitute spacer can be added to the assembly without disassembling the latter.

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: A spacer with a spring construction for the fuel bundle having matrix of parallel side by side fuel rods supported within a fuel channel between a supporting lower tie plate and holding upper tie plate is illustrated. The spacers each have a corresponding matrix of individual ferrules each surrounding the discrete fuel rods to be spaced within the matrix of fuel rods at any given elevation within the fuel bundle. Each of the individual ferrules surrounding the individual fuel rods are provided with stops against which the fuel rods are biased to ensure the required side-by-side spacing. Each ferrules must have at least one spring for forcing the fuel rods against the stops of its spacer ferrules to enable the spacer to assure required side-by-side alignment of the fuel rod. The springs are provided with a continuously looping main body having protruding tabs on opposite sides of the springs.

Abstract: A fuel assembly for a nuclear reactor includes a number of fuel rods filled with a fuel material. A plurality of fuel rods have a partial effective fuel area filled with a fuel material and has a portion in which enrichment of a fissile nuclide is significantly reduced or the fissile nuclide does not exist at all on an axial level including a reactor shut-down zone at which subcriticality becomes small during a reactor operation period. The other fuel rods are filled with the fuel material throughout the entire axial length thereof. The first mentioned fuel rod may be provided with a partially interposed zone or may be constructed by a fuel rod having a length shorter than that of the other fuel rod. The tube means may be arranged in the fuel assembly so as to pass the moderator therethrough.

Abstract: A nuclear fuel assembly with a debris filter. The lower end fitting of the fuel assembly has a stamped plate attached thereto that serves as a debris filter immediately upstream of the fuel rods. The stamped plate is provided with a plurality of flow holes in a size and pattern that provides filtration of debris damaging to the fuel rods while maintaining adequate coolant flow through the fuel assembly.

Abstract: A debris screen for a fuel assembly for a reactor to which coolant fluid is supplied comprises a substantially planar plate member having an array of coollant openings extending through the plate member dimensioned to trap at least a portion of debris particles carried by the coolant; and a skirt member enclosing the periphery of the plate member; each of the coolant flow openings having a coolant entry region at a lower surface, a coolant exit region at an upper surface and a coolant flow path extending between the entry and exit regions, the flow path including an intermediate segment laterally offset from the entry and exit regions to cause coolant to change direction of flow in the intermediate segment and thereby prevent at least a portion of the debris particles from passing through the plate members.

Abstract: A debris filter bottom nozzle of a nuclear fuel assembly is spaced below the lowermost grid, supports the guide thimbles, and is adapted to allow flow of liquid coolant into the fuel assembly. The debris filter bottom nozzle includes an enclosure defining a coolant flow chamber therethrough, and an upper transverse nozzle structure composed of a consolidated array of elongated cylindrical sections disposed across the chamber of the enclosure in side-by-side relation to one another, extending axially in the direction of coolant flow through the chamber, rigidly connected together and to the enclosure, and having tubular cross-sectional configurations defining passages for the coolant flow through the chamber.

Abstract: A fuel assembly has a water rod which consists of a coolant ascending path and a coolant descending path, the coolant ascending path opening below a fuel support of a lower tie plate, the coolant descending path opening above the fuel support and adapted to guide downwardly the coolant that has flowed up the coolant ascending path to the upper portion of the water rod. The lateral cross section of the coolant ascending path is more than 25 times that of the coolant descending path.The nuclear reactor with these fuel assemblies loaded in the core is operated as follows. After startup of the reactor when the reactor power is low, all the control rods inserted in the core are withdrawn completely. Then, the reactor power is controlled by regulating a liquid level formed in the water rods. This reactor operation method prolongs the lifetime of the control rods, thereby reducing the number of times they have to be replaced.

Abstract: A bottom nozzle plate for a fuel assembly in a nuclear reactor. The bottom nozzle plate is formed from a rigid substantially square plate having legs adapted to be positioned on the lower core plate of the reactor for supporting the fuel assembly above coolant inlet openings in the core plate. The rigid square plate has two types of coolant flow holes therethrough. The first flow holes are grouped in clusters of four to define a square pattern relative to the sides of the plate such that the width of the sections of the plate between the flow holes in each cluster is less than the width of the sections of the plate between the clusters of four holes. Each of the second flow holes is formed in an irregular pattern to define a substantially clover leaf shape. The second flow holes are positioned so as to be above the coolant inlet openings in the core plate when the bottom nozzle plate is installed in the reactor.

Abstract: A fuel assembly for a light water cooled and moderated nuclear reactor comprises a bundle of fuel rods and a structure for holding the bundle in position comprising upper and lower end pieces or nozzles joined together by guide tubes which support grids for maintaining the fuel rods at the nodal points of a regular array. The upper end piece comprises an adapter plate fixed to some at least of the guide tubes and having an upwardly directed shroud arranged to bear directly or indirectly on the upper core plate of the reactor and encircling a coolant passage defining an internal volume into which all guide tubes open. The adapter plate has coolant passages around the shroud. This arrangement makes it possible to direct an adjustable fraction of the cooling water flow outwardly of a cluster guide sleeve associated with the assembly and belonging to the upper internals of the reactor.

Abstract: A combination of flow trippers with spacer deflectors in the two phase steam/water region of a fuel bundle in a boiling water reactor is disclosed. Spacers with deflectors are placed immediately above the flow trippers. The flow trippers are located on either an inside channel wall surrounding the fuel bundle or the outside of water chambers within the fuel bundle. Additional flow trippers may be located adjacent to the spacers, above the flow trippers that are below the spacers. The spacers are provided with deflector skirts overlying the flow trippers. In operation of the fuel bundle, excess water flows in the two phase region in a film on the unheated inside walls of the fuel channel or the outside walls of the water chambers. The film flow is perturbed by the flow trippers and is deflected toward the fuel rods. The overlying deflector skirts or tabs on the spacers further deflect the liquid toward the fuel rods to improve cooling and to increase the power generation capability of the fuel bundle.

Abstract: An improved lower tie plate having increased fluid flow resistance is disclosed for use in a boiling water nuclear reactor. The fuel bundle includes the lower tie plate, an upper tie plate, and a plurality of fuel rods supported therebetween in vertical upstanding relation, with the fuel rods surrounded by a square sectioned channel. In the preferred embodiment, some of the upper fuel rods are of partial length. The surrounding channel confines the fluid flow through the fuel bundles between the tie plates for the extraction of heat from the fuel rods undergoing a fission reaction. The lower tie plate includes a first group of apertures for the support of the fuel rods to selected positions in the 9x9 matrix; appropriate numbers of these apertures are threaded for tying the upper and lower tie plates together with tie rods. The matrix is interrupted at larger apertures for the support of moderator containing water rods.

Abstract: A grid for a nuclear fuel assembly comprises a common frame having an axis and a plurality of beds of plates distributed along the axis. Each bed has a plurality of plates which are mutually parallel and are directed transversely to the plates of the adjacent beds. All plates are secured to the common frame. The plates having a same direction are distributed between a plurality of said beds interleaved with other ones of said beds consisting of plates having another direction, and the plates of the beds placed in an upstream portion of the grid have fins oriented so as to deflect coolant inwardly whereas the plates placed in a downstream portion of the grid have fins oriented so as to deflect the flow coolant outwardly.

Abstract: A fuel assembly for a nuclear reactor comprises a fuel bundle in which a number of fuel rods are regularly arranged and a channel box surrounding the outer periphery of the fuel bundle. The interior of the channel box is designed so that the inner cross sectional area of the channel box increases from the upstream side of the coolant flow towards the downstream side thereof, for example, by stepwisely shaving the inner surface of the channel box. The corner portions of the channel box may be chamfered to improve the stress due to the inner pressure.

Abstract: An intermediate mixing grid for nuclear reactor fuel assemblies is made without the usual perimeter strip. The ends of the grid members are formed so that they hold the fuel rods at the edges of the assembly in place.

Abstract: The apparatus comprises a body (13) housed in the bore (2, 5) of the assembly head (1) and a flow rate constrictor (12) housed in the sodium passage channel (4) in the assembly head (1). The body (13) comprises axial locking fingers (30) in the assembly head, which can be maneuvered by a slide block (20) actuated by an assembly manipulating device (9). The flow rate of coolant liquid circulating in the assembly may be easily adapted to the operating conditions of the assembly.

Abstract: The spacer-grid comprises at least one single-piece plate (1) through which extend a group of openings (2) at least a part of which constitutes an even network of passages (2) for the fuel rods and the guide tubes of the fuel assembly. The spacer-grid may be formed by one single-piece plate (1) of great thickness or by the association of a plurality of parallel single-piece plates interconnected by an outer girdle element.

Abstract: A spacer assembly for imparting a swirl to a passing steam water mixture within a fuel channel of a boiling water reactor is disclosed. The spacer assembly is placed at periodic intervals along the inside of a square cross sectioned fuel channel so as to separate the fuel containing rods from each other and the fuel channel sides. Each discrete spacer element is constructed of a matrix of helically twisted sheet metal spacing elements for the serendipitous purposes of providing separation of the steam and water, with water being deposited on the fuel rods surfaces. Each helical element is a twisted planar metallic member and includes a rotation of the metal surfaces in the order of 450.degree. over a typical two inches of length. For each 90.degree. interval of rotation from the top and bottom of each helical element, paired lattice connections are provided for attachment to adjoining elements. Intermediate of the lattice connectors at 45.degree.

Abstract: A debris filter bottom nozzle in a fuel assembly has support structure in the form of four legs adapted to rest on a lower core plate of the nuclear reactor and a nozzle plate fixed one side of the four legs facing toward a lowermost grid of the fuel assembly. The nozzle plate has defined therethrough only a plurality of flow holes individually smaller in size than the maximum dimension of unoccupied spaces through the lowermost grid which allow flow of liquid coolant through the nozzle plate. Therefore, any debris being carried by the liquid coolant flowing through the bottom nozzle from the lower core plate to the fuel assembly which is small enough in size to pass through the flow holes will also pass through the unoccupied grid spaces, whereas any debris which is large enough to not pass through the unoccupied grid spaces and collect in the grid will not pass through the aperture plate flow holes.

Abstract: In a nuclear boiling water reactor, an improved lower tie-plate and fuel channel interface for a boiling water reactor fuel bundle is disclosed. The fuel bundle has a lower tie-plate for supporting fuel rods and permitting the introduction of fluid interior of the fuel bundle. An upper tie-plate maintains the lower tie-plate supported rods in side-by-side relation and has apertures for discharging a mixture of water and steam. The fuel rods extend between the tie-plates for the generation of steam with some of the fuel rods forming a threaded connection fastening the tie-plates together. A polygon sectioned channel, preferably square, surrounds the tie-plates and fuel rods for the confining of fluid flow between the tie-plates interior of the bundle. The interface of the channel as it surrounds the lower tie-plate is reconfigured.

Abstract: In a nuclear fuel bundle having a lower tie-plate, an upper tie-plate and a surrounding channel therebetween, an improved water rod is disclosed for preferable use when fuel rods held between the tie-plates are placed in a 9 by 9 array. Typically, seven fuel rods are omitted centrally of the 9 by 9 array with the middle or fifth row having three rods removed and paired rods being removed in the 4th and 6th row with displacement of the removed pair towards opposite corners. Into the volume created by the removal rods, there are placed two "D" sectioned rods, the "D" rods each being round in cross-section except for a truncating chord, this truncating chord defining the straight back of each "D". In the preferred embodiment one of the "D" water rods is provided with spacer tabs for maintaining spacers separating the fuel rod at their correct elevations. This rod is inserted with an alignment that permits the tabs to pass through the spacers.

Abstract: A fuel assembly of the present invention comprises a plurality of fuel rods which are held by an upper tie plate and lower tie plate at the ends thereof and a moderating rod which is arranged between the fuel rods and held by the lower tie plate at its lower end. The fuel rods are arranged in a lattice form having 9 rows and 9 columns, and the moderating rod contains a passage for a coolant and has a cruciate cross-sectional form. The ratio A.sub.M /A.sub.C of the area A.sub.M of a moderator region in the moderating rod in the cross-sectional plane in which the moderator is present to the area A.sub.C of the coolant passages in said fuel assembly is within the range of 0.07 to 0.11, and the area A.sub.M is 75% or more of the total area of the fuel lattice units in which none of the fuel rods is arranged, but the moderating rod is arranged.

Abstract: A fuel assembly of the present invention comprises fuel rods which are arranged in 9 rows and 9 columns (9.times.9) in a channel box. The channel box has a width L between outer walls thereof and a width D between inner walls thereof, both of which satisfy the following equation:0.12.ltoreq.(P-L)/Dwherein P denotes the fuel assembly pitch in a reactor core. A sufficient cold shutdown margin for a reactor core can be secured by determining the widths L and D so as to satisfy the above-described equation, even if the average enrichment of the fuel assembly is increased to 4 wt % or more.

Abstract: A debris resistant bottom nozzle in a fuel assembly has a support structure in the form of four legs adapted to rest on a lower core plate of a nuclear reactor and a top flat plate fixed on one side of the four legs facing upwardly toward a lowermost grid of the fuel assembly. The flat plate is of a substantially solid configuration with a plurality of spaced cut-out regions defined therethrough in alignment with and directly above a plurality of inlet liquid coolant flow holes in the lower core plate. A plurality of open separate criss-cross structures are provided, each being fixed to the plate and extending across one of the cut-out regions therein within the plane of the plate.

Abstract: A nuclear reactor fuel assembly includes mutually parallel fuel rods and guide tubes for control rods. Two lattice-like spacers have mesh openings formed therein. One of the fuel rods or one of the guide tubes is guided and secured in each of the mesh openings. An additional lattice is secured at least to one of the guide tubes between the two spacers as seen in the longitudinal direction of the fuel rods and the guide tubes. The additional lattice has mesh openings formed therein defining sides of the mesh openings and a smooth and flat surface of the additional lattice in the mesh openings. Turbulence-promoting vanes protrude beyond the sides of the mesh openings formed in the additional lattice. One of the fuel rods is guided with play or one of the guide tubes is guided through each of the mesh openings formed in the additional lattice. Brackets grip the additional lattice between at least one of the fuel rods or the guide tubes at the outside of the fuel assembly.

Abstract: The invention relates to a nuclear reactor spacer grid member for use in a liquid cooled nuclear reactor and to a ductless core component employing a plurality of these spacer grid members. The spacer grid member is of the egg-shell type and is constructed so that the walls of the cell members of the grid member are formed of a single thickness of metal to avoid tolerance problems. Within each cell member is a hydraulic spring which laterally constrains the nuclear material bearing rod which passes through each cell member against a hardstop in response to coolant flow through the cell member. This hydraulic spring is also suitable for use in a water cooled nuclear reactor. A core component constructed of, among other components, a plurality of these spacer grid members, avoids the use of a full length duct by providing spacer sleeves about the sodium tubes passing through the spacer grid members at locations between the grid members, thereby maintaining a predetermined space between adjacent grid members.

Abstract: A Local Power Range Monitor (LPRM) string is employed between BWR fuel assemblies arranged in side-by-side spaced positions. The string has a hollow tube and neutron detectors located therein at spaced axial locations and being adapted to provide local power monitoring information. The hollow string tube is adapted to receive a neutron flux sensitive probe for calibrating the detectors. Each fuel assembly has an outer hollow tubular channel surrounding fuel rods and spacers disposed within and axially along the channel and about the fuel rods. The spacers are composed of a material incapable of producing a localized change in neutron flux. Elements in the form of strips of a neutron absorber material are attached to the exterior of the channel of each fuel assembly at a respective corner thereon and located axially at different known positions therealong and adjacent to the hollow string tube.

Abstract: Fuel assembly for the core of a nuclear reactor comprising spacing grids situated in the upper part of the assembly arranged at smaller intervals from one another than the grids situated in the lower part of the assembly. The upper grids ensure a more intense mixing of the coolant downstream than the lower grids, so as to reduce corrosion at the upper part and the temperature difference between the top of the sheath and the coolant.

Abstract: A fuel assembly for boiling water reactors includes, in addition to the usual outer flow channel which surrounds the fuel rods, an inner flow channel having rectilinear sides disposed within the fuel assembly, extending vertically therethrough, and arranged to receive cooling water at or below the bottom of the assembly. The channel is of such size as to span several cooling rods in each direction. A closure is provided in the channel within the critical heat flux zone of the assembly. At least one inner tube extends through the closure. The channel is closed at its upper end, and the inner tube is open at its upper end, which is located near the upper end of the channel. Egress openings are provided in the walls of the channel just above the closure. These openings are so positioned relative to the fuel tubes that jets of water emitted from them do not impinge directly on the fuel tubes, but rather enter the flow spaces between them.

Abstract: A nuclear reactor fuel assembly includes an elongated fuel channel with a square cross section and channel walls, the fuel channel having an imaginary lattice disposed therein with a box-shaped cross section having mesh openings and sides parallel to the channel walls, fuel rods containing nuclear fuel being mutually spaced apart in the mesh openings, and a prismatic water pipe spaced apart from the fuel channel by a given spacing and having a cross section spanning more than one of the mesh openings of the imaginary lattice, the given spacing being completely filled with the mesh openings of the imaginary lattice and the fuel rods disposed therein.

Abstract: A hollow flow deflector (10) for use in a nuclear reactor fuel assembly having spaced grids of orthogonal strips (16, 18) mounted for defining square matrices of aligned and supported cylindrical fuel elements (12, 14). The deflector has a central cylindrical opening (20), an upstream end portion (22), a downstream end portion (24) and an intermediate transition portion (26) joining the end portions. The hollow flow deflector (10) has a plurality of concave flow channels (30) regularly spaced about the periphery of the body in its downstream end portion. The flow channels (30) have their inlet portion defined in the transition portion (26) of the body (10).

Abstract: A spacing grid for a nuclear fuel assembly, particularly a water cooled assembly, includes two spaced sets of plates. Each set is formed of plates parallel to each other and fixed at their ends to a polygonal belt in the form of a strip having fins along one longitudinal edge at least. Each corner of the belt is free of openings. Two at least of the corners are rounded and located inside of imaginary extensions of the flat lateral faces of the belt. They are connected to the edges of the lateral faces by gussets sloping radially inwardly.

Abstract: A top nozzle adapter plate for use in a fuel assembly of a nuclear reactor includes an upper structural component and a lower functional component supported from the upper component. The fuel assembly has elongated structural members and fuel rods disposed in a predetermined array. The upper structural component of the adapter plate includes spaced and interconnected hubs and ligaments arranged to define substantial open areas for coolant flow therethrough while providing a rigid framework capable of transmitting lifting loads imposed by the fuel assembly. The hubs are connected to the elongated structural members of the fuel assembly.

Abstract: In a nuclear reactor, the core is composed of fuel assemblies disposed in side-by-side spaced relationships with an outer group thereof defining the periphery of the core and an inner group thereof positioned inwardly of the outer group. A baffle structure extends about the reactor core adjacent the fuel assemblies in the outer group. Any jetting of coolant fluid through the baffle structure will impinge upon fuel rods in the outer group of fuel assemblies so as to cause vibration of the fuel rods. To prevent such vibration, a plurality of annular anti-vibration grids are axially spaced along and connected to guide thimbles of the fuel assemblies in the outer group thereof between at least some of the support grids of such fuel assemblies. The annular grids are separate from and unconnected to the support grids.

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

Abstract: A marked reduction in the pressure drop of cooling liquid through a grid spacer of a nuclear fuel assembly is attained by convexly contouring the upstream (usually the lower) edges of the grid members. Preferably, they are made streamlined or semicylindrical. This can be done by first beveling and then etching them, by directing a stream of mixture of abrasive and an organic polymer against them, or by traversing an electron or laser beam along them at a power and velocity such as to cause local melting. A lesser improvement is secured by beveling alone. A still further improvement can be obtained by also tapering the downstream (usually upper) edges.

Abstract: A BWR fuel assembly has a bundle of spaced fuel rods, an outer tubular flow channel surrounding the fuel rods so as to direct flow of coolant/moderator fluid along the fuel rods, and a hollow central water cross with opposed walls, a lower flow inlet end, an opposite upper flow outlet end, and an open inner cruciform flow channel for subcooled moderator fluid flow through the fuel assembly. The water cross extends through the outer flow channel and is interconnected with the outer channel so as to divide it into separate compartments and the bundle of fuel rods into a plurality of mini-bundles thereof. Also, a pair of upper and lower tie plates are connected to the opposite ends of the fuel rods in each mini-bundle thereof so as to provide a separate fuel rod subassembly in each of the compartments. The tie plates have flow openings defined therethrough for allowing the flow of the coolant/ moderator fluid into and from the separate fuel rod subsasembly.

Abstract: In a channel contained fuel bundle for a boiling water nuclear reactor, an improved channel is disclosed. The channel contains a plurality of fuel rods held in spaced apart relation by at least upper and lower tie-plates and/or spacers. In the reactor, the channel contains fuel rods extending between a lower support plate and an upper support grid. When the reactor is operating, the channel confines water flow intimately about the rod bundle on the inside and assures steam generation in a predictable pattern. Water exterior of the channel is at a different and typically lower pressure. To accommodate control blades (which control the fission process) outside of the fuel bundles, the channel is provided with a polygon cross section, most typically a square cross section. In operation, the flat walls tend to bulge due to primarily pressure effects but also due to thermal and radiation effects.

Abstract: An improved channel is disclosed which has a reduced average thickness in its upper portion. The lesser average thickness corresponds to a lower pressure difference acting on the channel sides, over the upper portion of the channel. The reduction in average thickness is accomplished by cutting flow trippers into the inner surface of the channel walls and/or cutting grooves into the outer surface of the channel. The axial variation of channel average thickness increases water volume adjacent to the upper part of the channel to provide increased neutron moderation, to minimize the steam void reactivity coefficient, and to provide a greater cold shutdown margin. The material removed to produce the flow trippers increases the cross-sectional area inside the channel and reduces pressure drop in the upper portion of the channel. The flow trippers divert water flowing on the channel walls to the fuel rods adjacent to the channel walls, permitting higher reactor power operation.