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.

Abstract: A nuclear reactor fuel assembly bottom nozzle to guide thimble attachment system and method allowing bottom nozzle removal and replacement without inverting the fuel assembly. At manufacture, a bottom-insertable, two-headed bolt secures the bottom nozzle adaptor plate to the guide thimble bottom end plug. The two-headed bolt is unthreadable in the guide thimble from the top of the upright fuel assembly. At reconstitution, a top-insertable bolt fastener secures the replacement or original bottom nozzle adaptor plate to the guide thimble bottom end plug. The bolt fastener is inserted in the guide thimble from the top of the upright fuel assembly. The bolt fastener is unthreadable in the guide thimble from the top of the upright fuel assembly for a second reconstitution. Less preferably, the bolt fastener also can be used for original manufacture (in place of the two-headed bolts previously discussed).

Abstract: A BWR fuel assembly having an array of spaced fuel rods, an outer hollow tubular flow channel surrounding the fuel rods so as to direct flow of coolant/moderator fluid therealong, and a hollow central water cross extending through the channel and composed of radially extending members dividing the fuel rods into separate fuel rod mini-bundle subassemblies which each has fuel rod spacers being displaced from one another along the length of the subassembly, includes features on at least one of the spacers of each subassembly which minimize degradation of CHF performance. These features are coolant flow diverting scoops mounted on the outer peripheral strap of the spacer. The scoops are disposed in spaced apart relation along an upstream side of the outer strap so as to extend inwardly along and in spaced relation from an upstream side of respective ones of the terminal end portions of the interleaved inner straps of the spacer which with the outer strap form a ring of perimeter cell openings in the spacer.

Abstract: A grid for use in nuclear fuel assemblies is made up of double grid members which are deformed so as to provide channels for the coolant. At least the upper portions of these channels are inclined relative to the axes of the fuel rods and are disposed in such a manner as to cause circulation of fluid about each individual rod and within the assembly. In one embodiment the grid is positioned between the positioning grids and serves primarily as a coolant deflector. In another embodiment so constructed as to serve the positioning grid, as well as a flow deflector, the channels are straight in their lower portions i.e. parallel to the axes of the fuel rods. In their upper portions they curve to provide the desired deflection of the cooling fluid and the straight sections have a slight bow outward, relative to the plane of the grid member of which they are a part. This outwardly bowed portion engages the fuel rod and acts as a positioning spring.

Abstract: Fuel elements (16) support grids have openings (22,24) in the intersecting matrix strip (12,14) edges adjacent their points of intersection in which box-shaped conduit means (20) with integral mixing vanes (30 and 32) on the flow exit end (28) are secured. The vanes (30,32) create flow in two offset and oppositely transverse directions (34 and 36) relative to the direction of flow through the conduit means in order to generate thermal-hydraulic performance improving vortices (18) in the flow subchannels defined by the diagonal gaps between fuel elements (16). The box-shaped conduit means (20) also improve grid strength and rigidity.

Abstract: This invention is directed to a fuel assembly for boiling water reactors incorporating an advanced type of "water rod.

Abstract: A fuel assembly has a bundle of elongated fuel rods disposed in a side-by-side relationship so as to form an array 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, a hollow water cross extending centrally through and interconnected with the outer flow channel so as to divide the channel into separate compartments and the bundle of fuel rods into a plurality of mini-bundles thereof being disposed in the respective compartments, and a plurality of spacers axially displaced along the fuel rods in each of the mini-bundles thereof. Each of the fuel rods includes an outer cladding tube with an inner clad surface and a plurality of fuel pellets contained within the tube. Each spacer is composed of a plurality of interleaved inner straps and an outer strap encompassing the inner straps.

Abstract: Fuel array for an undermoderated nuclear reactor, comprising rods (6) arranged in a prism-shaped casing (1) parallel to the height of this casing (1). The internal surface of each of the walls (2) of the casing (1) is provided with channels (5) each of the channels (5) is located opposite a rod (6) arranged at the periphery of the array. The projecting parts (9) of the walls (2), between two channels (5), occupy part of the space between two peripheral rods (6). In this way, the moderating level remains constant throughout the cross-section of the array.The invention applies, in particular, to pressurized water reactors.

Abstract: A BWR fuel assembly having an array of spaced fuel rods, an outer tubular flow channel surrounding the fuel rods to direct flow of coolant fluid therealong, and a central water cross extending through the channel and dividing the fuel rods into separate subassemblies which each has fuel rod support spacers being displaced from one another along the length of the subassembly, includes features in each subassembly which minimize degradation of CHF performance. These features relate to intermediate flow mixing nonsupport grids disposed along each subassembly between and in spaced relation from the uppermost pairs of the spacers. The grid includes first and second groups of mixing vanes disposed at its downstream side. The vanes of the first group are attached on portions of the outer strap and on respective portions of the inner straps which together with the outer strap portions define the perimeter cell openings.

Abstract: A BWR fuel assembly having an array 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 extending through the outer flow channel and composed of respective pairs of spaced apart sheet members interconnected together at their outer and inner ends so as to define an open inner cruciform flow channel for subcooled moderator fluid flow through the fuel assembly and to the outer channel so as to divide the array of fuel rods into a plurality of fuel rod subassemblies, includes features which improve structural and hydraulic characteristics as well as CHF characteristics. The features which improve structural and hydraulic characteristics relates to closures in the form of perforated plates connected across the bottom and top ends of the sheet members of the water cross.

Abstract: In a nuclear reactor fuel assembly, a relatively flexible mounting member for mounting a large coolant conducting tube to the lower tie plate whereby excessive side forces on the fuel rod spacers are avoided in the event of lateral displacement of the fuel assembly such as during a seismic event.

Abstract: A fuel assembly for a boiling water reactor has a bundle of fuel rods consisting of a top tie plate and a bottom part which, together with a plurality of fuel rods, constitutes a rigid unit. The fuel rod bundle is surrounded by a fuel channel (1), to which there is attached a fixing member (2) cast in stainless steel. The fixing member (2) is attached to a vertical projection (3), extending from the top tie plate, by means of a bolt (4) which is loaded with a tensile force and a sleeve (10) which is loaded with a compressive force and which surrounds the bolt and is arranged in the fixing member, the coefficients of thermal expansion of the bolt and the sleeve being less than that of the fixing member.

Abstract: In a nuclear fuel assembly having a plurality of separate fuel bundles secured therein in separate compartments, coolant flow paths are provided to enable the flow of coolant between the separate compartments, thereby equalizing the hydraulic pressure between the separate compartments and minimizing the possibility of thermal-hydrodynamic instability between the separate fuel bundles in the nuclear fuel assembly. A plurality of coolant flow paths are formed through solid structural ribs secured to an outer flow channel of the nuclear fuel assembly to permit coolant flow between the separate compartments.

Abstract: A segmented fuel and moderator rod and fuel assembly for a BWR. The segmented rod has a lower fuel region and an upper moderator region for passing coolant having a void fraction of between about 0-20% through the upper portion of the BWR core which is normally undermoderated. The segmented rod displaces one or more conventional fuel rods in the fuel bundle. A method of moderating a BWR core is also disclosed.

Abstract: A debris trap is mounted within a bottom nozzle of a fuel assembly so as to capture and retain debris carried by coolant flowing from the lower core plate openings of the nuclear reactor to the fuel assembly. The trap includes a hollow enclosure disposed below the adapter plate of the bottom nozzle and between the corner legs of the nozzle. The enclosure is composed of upper and lower walls and a continuous side wall which spaces apart the upper and lower walls and interconnects their peripheries so as to form a debris capturing and retaining chamber within the hollow enclosure. The walls are composed of a material, such as wire mesh screen, which is permeable to liquid coolant but impermeable to debris. A plurality of wall sections severed from the lower wall and bent into the chamber of the enclosure define a plurality of openings into the chamber.

Abstract: A hollow water cross disposed in an outer flow channel of a fuel assembly so as to divide an array of fuel rods in the assembly into a plurality of subgroups is composed of a plurality of hollow panels which extend radially from a central axis of the water cross and define an open inner flow channel. The panels are interconnected at their outer ends with angularly displaced portions of the outer channel and at their inner ends with one another so as to define a central channel portion which extends the axial length of the water cross. The improvement relates to a cross brace disposed within the central channel portion of the water cross generally along the central axis thereof. The cross brace includes radially-extending portions which extend within and parallel to the respective water cross panels and interconnect with dimples formed in each panel so as to reinforce and stiffen the water cross and thereby the outer channel of the fuel assembly.

Abstract: An inlet nozzle assembly for directing coolant into the duct tube of a fuel assembly attached thereto. The nozzle assembly includes a shell for housing separable components including an orifice plate assembly, a neutron shield block, a neutron shield plug, and a diffuser block. The orifice plate assembly includes a plurality of stacked plates of differently configurated and sized openings for directing coolant therethrough in a predesigned flow pattern.

Abstract: A trap for catching debris carried by coolant flowing from the bottom nozzle of a fuel assembly to the bottom or lowermost one of the grids of the assembly which support the fuel rods in an organized array therein includes a structure disposed between the bottom nozzle and the bottom grid and generally aligned with the lower end plugs of the fuel rods. The structure forms a multiplicity of hollow cells each being open at opposite ends and defining a central cavity which receives one of the fuel rod lower end plugs while providing for passage of coolant flow therethrough from the bottom nozzle to the bottom grid. Also, the trap includes means in the form of dimples defined in each of the cells for catching debris carried into the cells by the coolant flowing therethrough. The dimples are formed from the wall portions defining the cells and extend into the cavities of the cells.

Abstract: A water cross for delivering non-boiling water to the center of a BWR fuel assembly for improved moderation and fuel economy. A cruciform skeleton is assembled from grid straps and connecting straps positioned at axial locations along stiffening rods. The skeleton is inserted into a flow channel to provide support for rectangular or square water tubes which are inserted through the skeleton into the flow channel to form an internal water cross. A method for forming a water cross is also disclosed.

Abstract: A fuel assembly for a nuclear reactor is provided with two access plugs in the adapter plate of the top nozzle whereby selected fuel rods can be removed and replaced without disassembling the assembly and while the assembly is in place in its operating position in the core region.

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

Abstract: A nuclear fuel spacer grid with improved grid straps. The grid has an egg-crate array of interleaved grid straps creating cells for enclosing the fuel rods. Near beginning of life in the reactor, the grid straps bend in a spring-like manner to flexibly grip the fuel rods with their preferably rigid protrusions. In a cell, the protrusions on two non-opposing grid straps are closed to longitudinal coolant flow while the protrusions on the remaining grid straps associated with the cell are open to such flow. Near end of life the grid straps loose resiliency due to irradiation--induced stress relaxation and the fuel rod has a loose fit against the protrusions due to radiation effects. However, the fuel rod is held in position in the cell by the coolant flow therethrough which forces the fuel rod away from the closed protrusions and into contact with the open protrusions. The protrusions in one cell are coplanar. The protrusions in the cells lie in one of two longitudinally separated planes.

Abstract: A nuclear fuel spacer grid with improved outer straps. The grid has an egg-crate array of interleaved grid straps creating cells for enclosing the fuel rods. The grid also has four outer straps connected together in a square-shaped array surrounding the grid strap's heightwise edges. The outer straps have a central portion to which is attached the grid straps' heightwise edges. The outer straps also have a top and a bottom resilient lengthwise border portion extending vertically beyond and horizontally outwardly beyond their associated outer straps central portions.

Abstract: A partial grid structure is provided for a nuclear reactor fuel assembly for selectively mounting either means for deflecting the upwardly flowing coolant or means for laterally supporting the fuel rods, or both, to substantially eliminate localized neutron flux peaking and thereby increasing the power output of the assembly. The grid structure extends across only a portion of the fuel assembly and is associated with a selective group of fuel rods defined by a predetermined number of the fuel rods contained within the fuel assembly. The grid straps form an egg-crate configuration creating cell openings for receiving the fuel rods of a predetermined fuel rod group. In an alternate embodiment, the fuel rods of the fuel assembly are partitioned into separate groups by the use of separate partial grid structures which are combined to form a grid structure assembly.

Abstract: A nuclear fuel element suitable for use in fast breeder. The fuel element has a clad tube and a wire spacer wound round the clad tube. The clad tube of the fuel element is composed of a first clad tube and a second clad tube which are connected to each other through an intermediate plug. The first clad tube extends upwardly from the intermediate plug. The upper end of the first clad tube is closed by an upper end plug, while the lower end of the second clad tube is closed by a lower end plug. The first clad tube is charged with a multiplicity of fuel pellets, while the second clad tube defines a gas plenum therein. The spaces inside the first and second clad tubes are communicated with each other through vent holes formed in the intermediate plug. The wire spacer is wound round the first clad tube and is fixed at its one end to the end plug attached to the first clad tube and at its other end to the intermediate plug.

Abstract: The present invention relates to an upper neutron protection device for a nuclear reactor assembly.This device comprises at least one container partly filled with a neutron-absorbing product and maintained within a wall located in the upper part of the assembly by at least one spacing plate.Application to fast neutron reactors.

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

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

Abstract: A reusable system for removably attaching the lower end 21 of a nuclear reactor fuel assembly duct tube to an upper end 11 of a nuclear reactor fuel assembly inlet nozzle. The duct tube's lower end 21 has sides terminating in locking tabs 22 which end in inwardly-extending flanges 23. The flanges 23 engage recesses 13 in the top section 12 of the inlet nozzle's upper end 11. A retaining collar 30 slides over the inlet nozzle's upper end 11 to restrain the flanges 23 in the recesses 13. A locking nut 40 has an inside threaded portion 41 which engages an outside threaded portion 15 of the inlet nozzle's upper end 11 to secure the retaining collar 30 against protrusions 24 on the duct tube's sides.

Abstract: An improved guide tube post which decreases the flow induced vibration of a cylindrical control rod suspended therethrough. The inner wall of the post, near where it exits into a diffuser region, is provided with a polygonal cross section. When, due to random fluctuation, the rod assumes an eccentric position near the wall of the post, the polygonal post geometry provides a relatively large angle between the post wall and the surface of the rod near the wall. It has been found that if this angle is too small, strong secondary flows develop along the length of the control rod and interact with other vortices in the diffuser region, to produce the vibration driving force. The polygonal cross section in the post modifies the secondary flow to reduce the intensity of the interaction with the diffuser vortices.