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: 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: An improved spacer is disclosed which contains an Inconel grid and a Zircaloy surrounding band. The Inconel grid can be fabricated from the extremely thin and highly elastic spring metal utilizing a modification of a prior art cell construction that includes paired inwardly bent vertical spring legs with cantilevered and rod encircling upper and lower arm pairs. The spring legs extend at spaced apart locations between the upper and lower arm pairs and have a medial spring rod contacting portion for biasing the rods into stops on the rod encircling arm pairs. The springs at the upper and lower ends are provided with spring dimple stops to prevent over stressing of the spring during assembly or handling of the fuel bundle into which the spacer is incorporated. The rod encircling arm pairs have an offset from center where the two arms meet at their distal ends to complete encirclement of the rods. This offset from center enables the cells to be fastened in cell pairs at their respective embracing arms.

Abstract: A spring-and-spacer assembly for maintaining fuel rods upright in a fuel assembly of a nuclear reactor core is provided. The spring is in the form of a continuous loop with first and second legs having mid-leg rod-contact regions. Bend regions are positioned on each side of each contact region extending toward the interior of the loop spring. In most positions, the spring is used to load two adjacent fuel rods. In configurations in which there is an unpaired fuel rod, a plate having a tab for contacting the spring is provided. The spring provides the desired force, such as about 2.5 pounds per fuel rod, in a small rod-to-rod spacing of less than about 0.14 inches.

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 cantilevered hold-down spring (68) for a nuclear fuel assembly (10), comprising an elongated metal bar including a substantially straight long leg portion (66) having one end adapted to be mounted (38) to a fuel assembly, an arcuate transition portion (70) at the other end of the long leg, and a straight short leg portion (76) extending from the transition portion at an acute included angle with the long leg portion, and a load transfer means (64) projecting from the straight leg intermediate the transition portion and the long leg first end. As the load on the primary loading point (80) on the transition portion increases, the load is transferred to the projection (64), thereby effectively shortening and stiffening the spring.

Abstract: The present invention provides a structural component for constituting a reactor core comprising one and the other metallic members arranged adjacent to each other in a reactor, and reduction means for reducing a difference in the swelling between the metallic members due to neutron irradiation thereto; a core of the reactor comprising a plurality of such constructural element; and a method for operating a reactor having metallic tubular members arranged in a core of the reactor and each enclosing a plurality of metallic cladding tubes in each of which substance heated by neutron irradiation thereto and cooled by passing coolant through the reactor core is filled, wherein the reactor is operated under a condition that an average used temperature of the cladding tubes is higher than an irradiation temperature that the swelling rate of the cladding material due to neutron irradiation thereto becomes maximum and an average used temperature of the tubular members is lower than an irradiation temperature that the

Abstract: An improved spacer and method of making a spacer is disclosed for use in a nuclear fuel bundle wherein a plurality of fuel rods enclosed within a channel are maintained in parallel side-by-side relation by a plurality of the spacers. Each spacer is placed within the fuel bundle at selected elevations between upper and lower tie plates. The improved spacer is a member of the class of spacers wherein solid strips of material are welded at interstitially placed tube members between the fuel rods to form the continuous spacer grid. The improvement constitutes forming separate upper and lower reduced section grids from separate, normally aligned, first and second parallel sets of grid members. One grid is formed for the top of the spacer; the remaining grid is formed for the bottom of the spacer. Tube members placed interstitially between the fuel rods are used to interconnect the grids.

Abstract: A spring-and-spacer assembly for maintaining fuel rods upright in a fuel assembly of a nuclear reactor core is provided. The spring is in the form of a continuous loop with first and second legs having mid-leg rod-contact regions. Bend regions are positioned on each side of each contact region extending toward the interior of the loop spring. In most positions, the spring is used to load two adjacent fuel rods. In configurations in which there is an unpaired fuel rod, a plate having a tab for contacting the spring is provided. The spring provides the desired force, such as about 2.5 pounds per fuel rod, in a small rod-to-rod spacing of less than about 0.14 inches.

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: To provide intrinsic reactor safety, the fuel sub-assemblies of a nuclear reactor core are provided with reactivity control mechanisms operable, in response to temperature rises above desired limits, to interact with adjacent fuel sub-assemblies and effect radial dilation of the core in order to reduce reactivity. Various embodiments are disclosed in which differential thermal expansion of an operating device or devices (34; 40; 42, 44, 46; 50) is translated into radially outward displacement of a lever or levers (28) for contact with neighbouring sub-assemblies.

Abstract: An inproved grid (16) for a nuclear fuel assembly (10), having a plurality of externally projecting, integrally formed anti-bowing springs (50) spaced about the grid perimeter plate (26), for interacting with flat surfaces (52') on the opposite grids (16') of adjacent assemblies (10'). The anti-bowing springs (50) are horizontally separated along each grid (26) in periodic alternation with substantially flat portions (52) of the perimeter plate (26). Preferably, each grid has a plurality of primary anti-bowing springs (70) that project a distance at least equal to the nominal gap (g) between assemblies, and a plurality of secondary anti-bowing springs (72) that are stiffer but project less than the primary springs. Also, backup springs (74) are disclosed as integrally formed ridges adjacent to the anti-bowing springs. The interaction of each grid (16) with its neighbor (16') "tightens" the core during power operation and provides an anti-bowing effect.

Abstract: To allow manipulation of the fuel assemblies in a nuclear reactor, the assemblies are provided with a lifting handle at the upper end. A top support is provided at the lifting end of the fuel assembly to determine the spacing. An upper end portion of the fuel channel for the fuel assemblies surrounds a lifting plate or the like for the fuel rods, where the lifting plate and handle together may form a lifting member cast in one piece. To simplify manipulation of the fuel assemblies during fuel inspection, for instance, and reduce the risk of losing small parts, a top support lock (1) for the top support (2) has been constructed in the handle (3). When assembling the top support (2), the top support lock (1) is moved to its open position and the angle-piece ends (5) are inserted through recesses (8) in the fuel channel (7) up to the openings (4) in the handle (3).

Abstract: A nuclear reactor fuel assembly having fuel rods containing nuclear fuel, includes a fuel assembly box in which the fuel rods are disposed, a head plate in the box having feedthroughs formed therein in which fuel rods are guided, at least some of the fuel rods being fastened to the head plate in the feedthroughs, a corner bolt disposed on top of the head plate, a cross piece disposed on the corner bolt at an upper inside corner of the box, an angular part disposed on two outer surfaces of the box, two leaf springs each extended in longitudinal direction of the box on a respective one of the two outer surfaces, a screw bolt connecting the box and the angular part to the corner bolt, the screw bolt having an expansion shank formed therein with a reduced diameter at the corner bolt, the screw bolt having a screw head with two ends, the screw head having a constriction formed therein between the ends thereof defining a coaxial screw head shank with a reduced diameter disposed in a hole formed in the angular part,

Abstract: A nuclear reactor fuel core assembly comprises an array of sub-assemblies comprising a central zone of fuel/breeder sub-assemblies (20F) surrounded by an annular zone of shielding sub-assemblies (20S). The fuel/breeder sub-assemblies (20F) are flexibly mounted from the reactor diagrid top plate 26 while the shielding sub-assemblies (20S) are mounted as stiff cantilevers so as to provide resilient restraint against bow of the central sub-assemblies (20S) during reactor operation, the restraint being exerted via abutment pads (40) at the level of the tops of the sub-assemblies (20S, 20F). The central core sub-assemblies (20F) also have abutment pads (34) at a lower level to form a lower restraint plane at this level controlling sub-assembly bowing in the central core zone.

Abstract: A nuclear reactor fuel assembly includes a fuel assembly box. A head plate is disposed in the fuel assembly box. Fuel rods containing nuclear fuel are disposed in the fuel assembly box and guided in leadthroughs formed in the head plate, at least some of the fuel rods being secured in the head plate. A corner bolt stands on top of the head plate. A cross bar is disposed inside one of the corners at the upper end of the fuel assembly box on the corner bolt. An angle element is adapted to the fuel assembly box. Each of two leaf springs are disposed on an outer surface of the angle element at a respective one of the sides of the fuel assembly box and extend in longitudinal direction of the fuel assembly box.

Abstract: A nuclear fuel assembly for a boiling reactor comprises a plurality of fuel rods arranged in four sub-bundles surrounded by a fuel channel of substantially square cross-section. A vertical channel-formed support member for the passage of water, separates the sub-bundles of fuel rods. By arranging each sub-bundle with a reduced corner portion by not locating a fuel rod in that corner of the sub-bundle towards the center of the fuel assembly, the sub-bundles can be located in a separating channel-formed support member with an enlarged central channel. The enlarged central channel makes it possible to contain a larger quantity of non-boiling water in the central part of the fuel assembly, which results in better neutron moderation in the central part of the fuel assembly.

Abstract: An upper end fitting 14 of a nuclear fuel assembly is provided at two of its opposite corners with spring retention caps 12 having a hook-like structrue defined by an inwardly directed flange 50 engaging a slot 56 in the top nozzle or end fitting 14. The spring packs 20 are retained within the spring retention caps 12 even if one or both spring retention screws 34 break and both the broken screw portions and the springs are maintained in operative position by the cap 12 until reconstitution.

Abstract: Liquid-cooled nuclear reactor having a reactor pressure vessel and a reactor core of fuel assemblies received therein, the fuel assemblies being grouped into core cells each having a control rod containing absorber material and connected to a drive mechanism, including a sheetmetal shaft associated with the core cells, respectively, and extending beyond the length of the reactor core by a length at least equal to that of the respective control rod and having a cross section substantially equal to that of the respective core cell, the sheetmetal shaft being formed with longitudinal channels through which the fuel assemblies are loadable and unloadable.

Abstract: Apparatus such as a nuclear fuel sub-assembly for use in a liquid alkali metal environment has bearing surfaces (4) coated with alumina or aluminide particles to reduce wear, fretting and friction. The particles are deposited by plasma or detonation gun using a nickel chromium alloy as a metallic bond.

Abstract: In a boiling water reactor (BWR) of the D-lattice type an improved apparatus and method for the mounting of a nuclear fuel assembly is disclosed. Specifically, a D-lattice nuclear fuel assembly is diagonally displaced at the top and diagonally displaced at the bottom to and toward the cruciform shaped control rod interstices. Displacement at the bottom end of the nuclear fuel assembly occurs by an eccentrically centered lower tie plate and fluid inlet for fitting to the core plate at the bottom end of the assembly. Displacement at the top end of the nuclear fuel assembly occurs by shims in the vicinity of the upper end of the channel at the top guides. The disclosed channel assembly is capable of installation during refueling cycles, with a displaced channel being substituted for prior art conventional D-lattice channels. Substitution of one displaced channel occurs with each refueling cycle in a group of four channels.

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.

Abstract: A fuel rod support grid having a quadrangular perimeter and fuel rod compartments defined by slottedly interlocking grid-forming members with openings in register intermediate the lines of intersection of the grid-forming members to provide accessible exposed edges for small nugget welds. The edge of one of two adjacent openings in register may define a weld enhancing tab. Typically, the pairs of openings in register and their small nugget weld are at two locations intermediate the line of intersection of two grid-forming members.

Abstract: The invention concerns a depository for radioactive waste and spent fuel cells comprising a concrete storage block in which several vertical storage and cooling channels are provided for accommodating the radioactive waste and the fuel cells. In order to provide an improved and safer concrete depository vis-a-vis the state of the art, the storage block is composed of several concrete blocks disposed beside and above one another. In the concrete blocks there are several vertical channels. The aligned channels of several concrete blocks placed on top of one another form storage and cooling channels for accommodating tubular storage containers for the radioactive waste and radioactive spent fuel cells. An annular gap is left for cooling air between the outer wall of the storage containers and the inner wall of the storage and cooling channels.

Abstract: A fuel assembly for a boiling water reactor has a fuel channel of generally square cross-section and provided with four walls, which fuel channel surrounds a plurality of fuel rods. Adjacent to its upper edge, the fuel channel is provided with a spacer having a corner portion and two arms extending from the corner portion and making an angle of 90.degree. with each other. The corner portion of the spacer engages a first corner of the fuel channel, and the two arms each make contact with the outer sides of the two fuel channel walls that meet at the first corner. Each arm is provided, at its outermost part, with a diagonally directed, horizontal projection which is inserted into a corresponding aperture in the adjacent fuel channel wall, the two projections thereby bridging across a respective one of the two corners of the fuel channel which are closest to the said first corner.

Abstract: A fuel assembly includes top and bottom nozzles, elongated hollow control rod guide thimbles extending longitudinally between and rigidly interconnecting the top and bottom nozzles such that together they form a rigid structural skeleton of the fuel assembly, transverse grids being supported on the guide thimbles at axially spaced locations therealong between the top and bottom nozzles, fuel rods extending through and being supported by the grids between the top and bottom nozzles so as to extend in generally side-by-side spaced relation to one another and to the guide thimbles, and elongated solid tie rods extending longitudinally between the top and bottom nozzles and through and rigidly interconnected with the grids so as to extend in generally side-by-side spaced relation to one another, to the fuel rods and to the guide thimbles so as to bolster the stiffness of the structural skeleton of the fuel assembly.

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 fuel assembly with a square cross section for water-cooled nuclear reactors, the fuel assembly having fuel rods disposed in a square array prescribed by spacers defining square grid meshes includes rods without fuel disposed, instead of the respective fuel rods, at individual positions of the square array distant from the marginal edge of the fuel-assembly cross section, for varying moderation ratio of the fuel assembly, the rods without fuel having a square cross section smaller than the cross section of the respective grid meshes only by a clearance sufficient for assembling the rods without fuel in the respective grid meshes and disassembling the rods without fuel from the respective grid meshes.

Abstract: A fuel assembly for a boiling water reactor comprises four bundles of vertical fuel rods (5). The bundles are surrounded by a common fuel channel (2) and each provided with a top tie plate (10) and a bottom tie plate (11). The four bottom tie plates are supported by a common supporting plate (18) which is inserted into, and supported by, the inlet sleeve (15) of the fuel assembly. Each bottom tie plate (11) includes an annular horizontal contact surface (24) abutting the supporting plate, and a non-round guide portion which is arranged, with no mentionable play, in a corresponding, non-round, through-hole (19) in the supporting plate (18).

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 nuclear fuel assembly channel spring and stop assembly having a separate channel spring assembly and stop assembly. A bi-directional channel spring is mounted by means of a plate to prevent rotation of the spring assembly relative to the upper fixture plate assembly of the fuel assembly. The stop member is formed integrally with the upper fixture plate assembly or mounted with a captive device to prevent rotation of the stop member relative to the upper fixture plate assembly.

Abstract: A top nozzle of a nuclear reactor fuel assembly is removably mounted to the guide thimbles of the fuel assembly by mating and unmating of pluralities of outer and inner sockets defined in the respective top nozzle and guide thimbles. A bearing plate supported on the top nozzle and movable relative thereto between a lower, non-release position and an upper, release position supports a plurality of locking tubes which are inserted at their lower end portions into the outer sockets. When the bearing plate is at its non-release position, the lower end portions of the locking tubes are inserted into the inner sockets and prevent them from unmating from the outer sockets and thereby retain the top nozzle mounted to the guide thimbles. However, when the bearing plate is at its release position, the locking tube lower end portions are withdrawn from the inner sockets and allow them to unmate from the outer sockets and thereby allow lifting of the top nozzle off and removal from the guide thimbles.

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 mechanically attached load pad for the duct of a liquid metal nuclear reactor fuel assembly.

Abstract: A boiling water reactor fuel assembly is provided with an elongated, vertical stiffening device having four stiffening wings (4) which are each attached to a wall of the fuel box. Each stiffening wing has at least one vertically directed passageway for water. The stiffening device has a cruciform cross-section and is composed of four elongated members (6, 6', 6", 6'") of L-shaped cross-sections.

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: Nuclear fuel assemblies having square cross-sections mount tubes at each corner, the tubes containing springs which are extended through apertures in the tube walls when actuated by solid rods extended down into the tubes by the weight of the upper guide structure of the nuclear vessel in which the fuel assemblies are mounted. The springs, extended from strategically located positions along the length of the tubes, engage the surface of adjacent fuel assemblies to dimensionally stabilize the fuel assemblies relative to each other and the vessel in which they are mounted.

Abstract: Method of loading or unloading or both loading and unloading a nuclear reactor, wherein control rods of cruciform cross section are at least partly withdrawn, each of the control rods being associated with a respective group of four fuel assemblies respectively having elongated duct tubes of rectangular cross section and being disposed in respective corners of a rectangular mesh of a transverse support grid, the duct tubes forming therebetween a gap-shaped intermediate space of cruciform cross section for accommodating a respective one of the control rods of cruciform cross section, which includes, prior to withdrawing a respective control rod associated with the respective group of four fuel assemblies, unloading from the nuclear reactor at least one of the four fuel assemblies of the group thereof, and inserting a support member into the respective mesh so as to fix in the respective corners of the mesh the ends of two diagonally opposed fuel assemblies of the group remaining in the nuclear reactor; and sup

Abstract: A storage device for receiving spent nuclear fuel elements comprising a plurality of chambers which are separated by partitions from each other. The partitions form arches in such a way that relatively large arches alternate with relatively small arches. Each arch of relatively large size engages physically an arch of relatively small size, and vice versa. Considering two contiguous identical partitions, this implies that the partitions are arranged out of registry.

Abstract: A rack is provided for either temporary or permanent storage of spent nuclear fuel assemblies. The rack consists of a checkerboard array of substantially square cells. Alternate cells in each row include neutron-absorbing poison material, either in the cell wall or otherwise, while the other cells are storage cells for the fuel assemblies. For temporary storage, the poison cells also contain a moderator which may be water or which may be a solid hydrogen compound. For permanent storage fuel assemblies that have decayed to a lower level of radioactivity, the moderator is eliminated so that all the cells can contain spent fuel assemblies, and the entire rack structure is encased in concrete for shielding.

Abstract: The present invention relates to a device for fixing a spring to a spacing grid for fuel elements of nuclear reactors.This device is characterized in that it is constituted by two retaining bridges (8) for the spring (6) made in one of the thin metal sheets constituting the grid and maintaining the spring (6) against said sheet. Two other bridges (10) located outside the bridges (8) constitute abutments for stopping the translation of the spring (6). A double stamping (12) made in the thin metal sheet at the approaches of each retaining bridge (8) constitute a precise translation guide for the spring (6).Application to the spacing grids of fuel elements of nuclear reactors.

Abstract: A fuel assembly for the core of a boiling water nuclear reactor has a plurality of boxes each surrounding a respective bundle of fuel rods. These boxes, are connected at one end to a common bottom unit, intended to be connected to an opening in a supporting plate in the core, and are also connected at their other end to a common top unit. The boxes may be detachably connected to the bottom portion and the top unit and be relocatable within the fuel assembly. Alternatively, the bundles of rods may be arranged for easy withdrawal from the boxes to enable transfer of the rod bundles between the boxes.

Abstract: A pad of a fuel assembly with a wrapper tube is pressed out from the interior of the wrapper tube to provide a band-like pad. The pad is reinforced by a reinforcing member fitted in a hollow portion of the pad. The pad is joint to the reinforcing member, or made so that swelling of the pad does not exceed that of the reinforcing material.

Abstract: Fuel assembly for boiling water reactors formed of a cluster of fuel rods held by a head piece and a base, respectively, at opposite ends thereof and surrounded by a coolant-flow guiding casing with the aid of a fastening angle includes leaf springs carried by the fastening angle for mutually spacing the fuel assembly from and mutually clamping it with a multiplicity of other fuel assemblies combinable therewith into a reactor core, the leaf springs extending in axial direction of the fuel assembly and having both ends thereof in contact with the fastening angle, one of the ends being rigidly held by the fastening angle, and the other of the ends being slidingly held on the fastening angle.

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.