Abstract: The lower end of each of a plurality of fuel rods is supported by a fuel supporting portion of a lower tie plate. The fuel supporting portion includes a plurality of second coolant paths for supplying a coolant from below the fuel supporting portion to a first coolant path defined above the fuel supporting portion and between the fuel rods. The total cross-sectional area of all the second coolant paths is smaller than the cross-sectional area of the first coolant path.

Abstract: A nuclear fuel assembly for a boiling water reactor, comprising an outer channel having a substantially square cross-sectional area, and fuel rods arranged with a predetermined pitch in an array of 10.times.12 where the centers of the fuel rods are located at the vertices of equilateral triangles.

Abstract: A fuel assembly for a nuclear reactor vessel includes a plurality of fuel rods, at least one coolant rod, a lower tie plate supporting the fuel rods and coolant rod, and a channel surrounding the fuel rods, coolant rod and tie plate. The lower tie plate is supported by the channel such that the channel carries a load of the fuel assembly. In one aspect of the invention, an upper tie plate includes two spring loaded latch pins engageable with corresponding apertures in the channel. A transition member supports the lower tie plate and is rigidly secured to the channel. Thus, when lifting the fuel assembly from the reactor, the channel bears the load of the fuel assembly. End gussets or clips are welded to the channel and inserted into the transition member, which serve as a secondary support for the transition member in the event that its primary connection to the channel fails. A channel guide member is secured to the, upper tie plate and includes two ears that are received in ear apertures in the channel.

Abstract: A fuel assembly for a nuclear reactor vessel includes a plurality of fuel rods, at least one coolant rod, a lower tie plate supporting the fuel rods and coolant rod, and a channel surrounding the fuel rods, coolant rod and tie plate. The lower tie plate is supported by the channel such that the channel carries a load of the fuel assembly. In one aspect of the invention, a conventional upper tie plate is removed and a handle assembly is provided that includes two spring loaded latch pins engageable with corresponding apertures in the channel. A transition member supports the lower tie plate and is rigidly secured to the channel. Thus, when lifting the fuel assembly from the reactor, the channel bears the load of the fuel assembly. If it is desired to remove the fuel bundle from the channel, the handle assembly is released from the assembly by releasing the latch pins.

Abstract: In a fuel bundle for a boiling water nuclear reactor comprising a plurality of fuel rods (20) secured within an array and extending between upper and lower tie plates (24, 22), and including at least one additional partial length fuel rod (20') extending from said lower tie plate (22) but terminating short of said upper tie plate (24), an improvement in the form of a removable extension rod (32) secured to said at least one additional fuel rod (20') and extending substantially to said upper tie plate (24). The removable extension rod (32) also permits variance in the reactivity of the partial length fuel rod (20') particularly in the two phase region of the bundle (10).

Abstract: A boiling water reactor fuel assembly with fuel rods having variable fuel rod pitches.

Abstract: In a fuel bundle assembly (B) for a nuclear reactor wherein a plurality of fuel rods (R) and at least one water rod (W) extend between an upper tie plate and a lower tie plate, an improvement includes a fixed connection between the water rod (W) and the lower tie plate (L), the fixed connection including a threaded lower end plug of the water rod and a threaded hole in a boss formed in the lower tie plate adapted to receive the threaded lower end plug, the threaded lower end plug (50) formed with a diametrical slot (54) therein and the boss (56) formed with a pair of slots (60, 62) extending from opposite sides of the hole such that the diametrical slot (54) and the pair of slots (60, 62) are alignable when the threaded lower end plug (50) is threaded into the boss (56); and a key (64) insertable within the aligned slots to thereby fix the water rod against rotational movement.

Abstract: A fuel assembly has part length and full length fuel rods, and a pair of large-diameter water rods which occupy an area which can accommodate 7 fuel rods. Natural uranium regions are provided in the upper and lower end portions of the effective fuel zone of the fuel assembly. An intermediate region between these upper and lower natural uranium regions provides an enriched uranium region which has three axial sections: an upper section, a middle section and a lower section. The middle section has the highest average enrichment, the lower section has the medium average enrichment and the upper section has the smallest average enrichment. The difference in the average enrichment between the middle section and the lower section is smaller than that between the middle section and the upper section. The upper section has a lower concentration of burnable poison than other sections of the enriched uranium region.

Abstract: A fuel assembly is provided with a coolant ascending path for making coolant rise and a water rod having a coolant descending path for conducting the coolant.A ratio of a flow area in a coolant inlet port of the smallest in coolant ascending path 13 on the downstream side than large diameter tube portion 3E to a flow area of the largest in the axial direction of coolant ascending path 13 in large diameter tube portion 3E is set to be 0.2-20%.In the normal operation, the declination degree from the liquid level in the coolant ascending path, corresponding to the coolant flow rate of the liquid level formed in the coolant ascending path can be controlled. Further, at the time of the excess the change speed of the liquid level can also be controlled.

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

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

Abstract: A fuel bundle assembly for a nuclear reactor, wherein a plurality of fuel rods and at least one water rod extend between an upper tie plate and a lower tie plate, includes upper end plugs secured to a pair of water rods and having axial cut-out portions defined by upper and lower shoulders. A latching mechanism for securing the pair of water rods to the upper tie plate includes a latch bar mounted on an upper surface of the upper tie plate and rotatable into and out of the cut-out portions in the end plugs when the end plugs extend above the upper surface of the tie plate upon installation of the upper tie plate on the fuel bundle assembly. A locking pin is provided which prevents the latch bar from being accidentally unlocked.

Abstract: A nuclear fuel assembly for a boiling water reactor having a spacer grid for positioning and retaining the fuel rods. The spacer grid comprising an upper grid structure and a lower grid structure. Each grid structure comprises a first set of grid strips and a second set of grid strips which intersect to form in each grid structure a lattice of rectangular and square shaped cells through which the fuel rods extend and which act against the fuel rods within the cells. The lattice in each of the upper grid structure and the lower grid structure being the same. The upper grid structure and the lower grid structure being oriented relative to one another so that each of the rectangular and square shaped cells in the upper grid structure is superimposed on a corresponding one of the rectangular and square shaped cells in the lower grid structure so as to act cooperatively against and provide support to a fuel rod on four sides of the fuel rod.

Abstract: A fuel assembly comprises fuel rods arrayed in a square lattice pattern of 10 rows and 10 columns, and three large-diameter water rods arranged along a diagonal line of the fuel assembly in such a region as able to accommodate 10 fuel rods. Partial length fuel rods are arranged in an outermost layer of the fuel rod array at fuel rod setting positions other than corners of the outermost layer. Ordinary fuel rods are arranged in a layer inside the outermost layer and adjacent to the outermost layer at positions adjacent to the partial length fuel rods in the outermost layer.The struction of the fuel assembly enables a reduction in the void coefficient and an improvement in the reactivity control capability. Also, the void coefficient can be reduced without lowering reactivity, and fuel economy is improved.

Abstract: A fuel assembly and a reactor core using same which are able to increase size of the fuel assembly with ensuring thermal margin and reactor shut down margin.A distance between centers of adjacent fuel assemblies is about 23 cm, which is enlarged about 1.5 times of conventional fuel assemblies. A thickness of water gap region is about 16 cm, which is relatively thinner than that of prior art. While, H/U ratio is about 5 as same as that of the prior art, and decreasing amount of non-boiling water in the water gap region is arranged in a channel box as water rods. Consequently, a ratio of transversal cross section area of the water rods to transversal cross section area of the fuel rods becomes about 0.6, and local power peaking factor can be decreased and thermal margin can be increased. Further, the transversal cross section area of the water rod is selected to be 15 cm.sup.2 so as to ensure the reactor shut down margin by reducing excess reactivity.

Abstract: A fuel assembly includes a cluster of mutually parallel fuel rods. A fuel assembly channel laterally surrounds the cluster of fuel rods and has a substantially rectangular cross section and flat channel walls. Grid-like spacers having meshes formed therein each receive a respective one of the fuel rods for guiding the fuel rods in a plurality of axial positions. At least one support spring laterally supports each respective one of the fuel rods in the mesh guiding the fuel rod. Each of the spacers have inner ribs being aligned parallel to the fuel rods and outer peripheral ribs opposite the channel walls. At least some of the inner ribs are fastened to the peripheral ribs, and the outer peripheral ribs are joined together only by the inner ribs.

Abstract: An object of the present invention is to provide a boiling water reactor wherein two phase flow instability in a fuel assembly occurs scarcely.A bottom flow path is formed beneath a partition plate which is supported by control rod driving mechanism housings in a reactor pressure vessel, and coolant guide tubes which open beneath the partition plate stands perpendicularly on the partition plate. An upper end portion of the coolant guide tube is restrained at outer periphery by a fixing portion of a square grid, and a coolant entrance of a fuel assembly is connected through to the coolant guide tube.Pressure loss of the coolant decreases and flow instability of the coolant in the fuel assembly occurs scarcely, lowering of a critical power ratio at a pump trip can be suppressed.

Abstract: An improved fuel rod is provided having a part-length fuel rod portion that improves performance with respect to typical part-length fuel rods without significant degradation of the benefits that are achieved by using such a system, e.g., improved fuel utilization, stability, and shut down margin. The present invention provides a fuel rod for a light water nuclear reactors that comprises a part-length fuel rod and an extension tube having at least one wall member defining an enclosed flow path therethrough, the extension tube being coupled to a portion of the part-length fuel rod so as to be disposed axially above the part-length fuel rod, and including at least one inlet opening, for allowing fluid that surrounds the rod and initially comprises a two phase mixture of steam and liquid, to enter the enclosed fluid path and at least one outlet opening located above the inlet opening, the extension tube includes means for separating at least some of the steam located in the fluid from the liquid located therein.

Abstract: An improved fuel rod is provided having a part-length fuel rod portion that improves performance with respect to typical part-length fuel rods without significant degradation of the benefits that are achieved by using such a system, e.g., improved fuel utilization, stability, and shut down margin. The present invention provides a fuel rod for a light water nuclear reactors that comprises a part-length fuel rod and an extension tube having at least one wall member defining an enclosed flow path therethrough, the extension tube being coupled to a portion of the part-length fuel rod so as to be disposed axially above the part-length fuel rod, and including at least one inlet opening, for allowing fluid that surrounds the rod and initially comprises a two phase mixture of steam and liquid, to enter the enclosed fluid path and at least one outlet opening located above the inlet opening, the extension tube includes means for separating at least some of the steam located in the fluid from the liquid located therein.

Abstract: A fuel assembly for a light water reactor comprising a plurality of fuel rods which contain plutonium as a primary fissile material when exposure is zero, and a light water reactor including such fuel assemblies. The fuel assembly has a structure in which at least one of moderator rods is provided at least in one of each corner portion of an arrangement of the fuel rods and a position adjacent to the corner portion in such a manner that the moderator rods are located in rotation symmetry, each of the moderator rods being filled with water or a solid coolant over a length at least corresponding to a fuel effective length, and the fuel rods are provided at positions in the second layer from the outermost periphery which are adjacent to those positions at which the moderator rods are located.

Abstract: In a fuel assembly, lower end pieces of fuel rods, guide tubes and coolant pipes, etc., are inserted and/or screwed into a base plate and secured against lifting by a bolt. In the case of fuel rods, in particular fuel rods which do not extend over the entire length of normal rods, the bolt is screwed onto connecting parts in such a way that a releasable bayonet closure is produced. In the case of coolant pipes of boiling water reactors, there is provided in particular a screw connection which is irreleasably secured against torsion by the bolt.

Abstract: A rectilinear sectioned water rod--preferably of square cross-section--is provided with horizontal grooves for keying to bands on the inner, water rod surrounding aperture of spacers. Each spacer is constructed preferably of Inconel and includes a specialized inner band for keying to the water rod. The inner spacer member includes an upper surrounding band, a lower surrounding band, and four connecting vertical members--one positioned at each corner of the water rod. Two adjacent vertical members are bent inward to contact one side of the water rod at spaced apart points on the corners of the water rod. The remaining two adjacent vertical members are bent inward to contact the remaining two corners at single points on each vertical member.

Abstract: An improved fuel rod is provided having a part-length fuel rod portion that improves performance with respect to typical part-length fuel rods without significant degradation of the benefits that are achieved by using such a system, e.g., improved fuel utilization, stability, and shut down margin. The present invention provides a fuel rod for a light water nuclear reactors that comprises a part-length fuel rod and an extension tube having at least one wall member defining an enclosed flow path therethrough, the extension tube being coupled to a portion of the part-length fuel rod so as to be disposed axially above the part-length fuel rod, and including at least one inlet opening, for allowing fluid that surrounds the rod and initially comprises a two phase mixture of steam and liquid, to enter the enclosed fluid path and at least one outlet opening located above the inlet opening, the extension tube includes means for separating at least some of the steam located in the fluid from the liquid located therein.

Abstract: A reactor core for a boiling water nuclear reactor comprises a plurality of vertical fuel assemblies (40a, 42, 44), each one containing a plurality of fuel rods (10), which are arranged between a bottom-tie plate (11) and a top-tie plate (12) in a surrounding vertical casing (6) and which extend through a number of spacers (13, 13a-f) which are arranged in spaced relationship in the vertical direction and which together with the bottom-tie plate and the top-tie plate retain the fuel rods in spaced relationship in the lateral direction. Each fuel assembly is designed with an inlet (3) for water for conducting water in through the bottom-tie plate, through the space between the fuel rods in the vertical casing, and out through the top-tie plate.

Abstract: In order to obviate the use of supporting rods, an upper end piece of a coolant tube penetrates a fuel assembly head of a nuclear reactor fuel assembly and is supported on the fuel assembly head. A lower end piece of the coolant tube is fastened to and supported by a fuel assembly foot, in particular with rods of partial lengths. A supporting skeleton therefore includes the foot and the coolant tube with spacers. The fuel assembly head and a handle are placed on the skeleton and screwed onto the coolant tube after fuel rods are pushed into meshes of the spacer.

Abstract: A reactor core with each fuel rod surrounded by an individual cylindrical channel is disclosed. This individual channel on each fuel rod provides thermal hydraulic and heat transfer advantages to enable all fuel rods within the fuel bundle to uniformly approach their own thermal limits. The preferred fuel rod pitch is a triangular pitch between the individual fuel rods as they are discretely surrounded by their own channel. The new triangular geometry provides for more uniform (flat) power distributions within all fuel rods--and hence all groups of fuel rods. Bypass flow is introduced uniformly between the fuel rod channels, rather than heterogeneously in the channel gap and water rods as in present BWR fuel designs. Individual fuel rod channels can be orificed differently, as required, to match inlet flow to fuel rod power output to maintain uniformity between all fuel rods as they approach their respective thermal limits.

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

Abstract: A low pressure drop spacer for positioning and retaining the fuel rods of a nuclear fuel assembly in which a plurality of upper and lower spring forks which extend through apertures in the side wall of the spacer into the assembly and through apertures in grid members which divide the assembly. The intersection and superposition of the spring forks, side wall and grid members form fuel rod passageways through which the fuel rods extend.

Abstract: In a fuel bundle for a boiling water nuclear reactor, modification of the spacers at the peripheral spacer band is made to maintain a more uniform spacing of the peripheral fuel rods from the channel walls to avoid critical power limitations. The conventional fuel bundle construction include a plurality of side-by-side sealed vertically disposed nuclear fuel rods in a square array supported at a lower tie plate, at least some of the fuel rods fastened to an upper tie plate, and held in designed spaced apart relation as a unitary mass by intermittent vertically placed spacers. A square sectioned channel surrounds the upper tie plate, the lower tie plate, and the fuel rods and spacers therebetween. The square sectioned channel functions to confined fluid flow interior of the fuel bundle between the tie plates and through the fuel rods. At the same time, the channel separates a core bypass region exterior of the channel having high moderator density from the flow path interior of the fuel bundle.

Abstract: A fuel assembly for a boiling water nuclear reactor is provided comprising an elongated central water channel including wall members that define an enclosed fluid flow path therethrough, the channel includes a lower opening for receiving water and allowing water to flow through the fluid flow path and at least one outlet opening. At least one partial water rod is provided that is coupled to a partial fuel rod so as to be disposed axially above the partial fuel rod. The partial water rod includes an inlet opening in fluid communication with the outlet opening of the central water channel so as to allow water to flow from the water channel into an interior of the partial water rod.

Abstract: An improved lower end fitting 10 (L.E.F.) having a bell mouth multistage type of flow jet diffuser 30 with stages 31, 31' decreases pressure drop 15-20% over a single stage bell mouth diffuser and more evenly distributes flow and adds strength. It includes neutron thimble flux impingement shield 50 of instrument and/or cable. Each diffuser stage 31, 31' is S.S., of circular cross-sect. and parabolic to optimize diffusion. The multistage shape is based on lower core plate 20 flow hole 24 geometry, L.E.F. design and reactor flow rate. Thinner L.E.F. legs 36, smaller L.E.F. gussets 38 and thinner L.E.F. flow plates 22 are possible.

Abstract: A fuel assembly included a plurality of fuel rods, fuel spacers for maintaining gaps between the fuel rods and a channel box. The channel box includes spacer support portions projecting inwardly from an inner surface of the channel box and supporting the fuel spacer in a transverse direction and creep deformation inhibition portions disposed at the lower end portion of the channel box and projecting inwardly. The distance between the spacer support portions disposed to oppose one another in a horizontal direction is smaller than the distance between the creep deformation inhibition portions opposing one another in the horizontal direction.

Abstract: A water rod is disclosed in combination with a fuel bundle for a boiling water nuclear reactor in which water is introduced to the water rod directly from the high pressure lower plenum below the reactor core. This introduced water circulates upwardly and centrally through the water rod to the top of the water rod. Thereafter, the water flows peripherally downward adjacent the exterior of the water rod. The introduction of water to the water rod directly from the high pressure water plenum below the reactor core provides sufficient pressure to maintain water flow through the water rod and to prevent flashing of the water passing through the circuitous path of the water rod to steam. Thereafter, the water is discharged at the bottom of the fuel bundle with water entering the steam generation path through the lower tie plate so that the discharged water participates in the steam generating flow path within the fuel bundle.

Abstract: A nuclear fuel assembly for a light water reactor includes an axially directed shortened water channel, truncated between an uppermost spacer and an upper tie plate. A boat-tail shaped end fitting is mated to the truncated end of the water channel, with their mated outer surfaces forming a smooth tangential substantially continuous surface therebetween. Opposing outer side surfaces of the end fitting are substantially convex, and inwardly tapering toward one another in a continuously curved manner, with the side surfaces terminating to form a top aperture. The aperture provides for the exit of coolant moderator from the water channel, and is sized to equalize the internal flow velocity of coolant moderator exiting from said aperture to the external coolant moderator flow velocity at said aperture.

Abstract: Part length water regions are located above part length fuel rods in boiling water nuclear reactor fuel bundles. The part length water regions include discrete containers having entry ports at the top of the part length water regions for capturing water, and vent ports for permitting internally generated steam to escape. The advantages of improved neutron moderation in the upper portion of the fuel assembly are maintained while the uranium fuel removal requirements are minimized.

Abstract: A fuel assembly for a boiling water reactor includes an elongated case having a bottom, a top and an interior. A base part covers the bottom of the case and has inlet openings formed therein for a liquid coolant acting as a moderator. A head part covers the top of the case and has outlet openings formed therein for a liquid/steam mixture of the coolant. At least one throttle restriction is disposed in a cross-sectional plane between the head part and the base part. A portion of the coolant flows along and between a bundle of fuel rods which are disposed parallel to one another and to the case in the interior of the case. A portion of the liquid coolant is guided through the at least one tube. The at least one tube is disposed parallel to the rods in the bundle between the base part and the head part. The at least one tube has lateral outlet openings formed therein upstream of the cross-sectional plane of the throttle restriction.

Abstract: A fuel bundle for a boiling water nuclear reactor having an improved water rod is disclosed, this water rod having two discrete compartments upper and lower for containing water. The bottom compartment flows moderator from the bottom of the fuel bundle through the water rod compartment to discharge points located through the water rod side walls between the upper most spacers; the top compartment opens upwardly and is naturally filled with liquid moderator settling out of the upwardly flowing moderator during reactor operation. There results the requisite presence of liquid moderator within the water rod for supplying the upper two phase region of the fuel rod with nearly full moderator density. At the same time, water flow through of the water rod from the bottom of the fuel bundle to the upper two phase region of the fuel bundle improves the thermal hydraulic performance.

Abstract: A fuel assembly of a pressurized water nuclear reactor includes at least two fuel rods, respectively, having a cladding tube of given outer and inner diameters and pellets of given outer diameter received in the cladding tube, the fuel rods being disposed in the fuel assembly at a given mutual spacing of center points thereof, a ratio of the given mutual spacing of the center points of the fuel rods to the outer diameter of the cladding tube being in a range between 1.35 and 1.37.

Abstract: A fuel bundle and fuel bundle assembly sequence utilizing a peanut sectioned large water rod is shown locking spacers into place along the axial length of the water rod. In a first embodiment, clearance is defined relative to tabs welded on the large water rod so that spacer assembly to the water rods can occur. In a second and preferred embodiment, spacers are individually equipped with springs locking into complimentary apertures in the peanut sectioned water rod. In both embodiments, the spacers are threaded onto the peanut sectioned water rod and locked into alignment for the receipt of the fuel rods. An improved suspension of the water rod relative to the lower tie plate is disclosed in which a transition piece connects the large water rod to a flexible rod which is threaded at its lower end. This rod is screwed into a threaded aperture in the lower tie plate.

Abstract: A fuel bundle of square cross section and standard vertical dimension is disclosed. The fuel bundle includes a matrix of upstanding vertical rods, a lower tie plate for supporting the matrix of vertical rods and permitting the inflow of liquid moderator coolant (preferably light water), and upper tie plate for holding the matrix of vertical fuel rods upright and permitting the outflow of liquid and vapor moderator coolant (water and steam), and a preferably square sectioned channel extending between the tie plate for confining the flow path between the tie plate around the fuel bundle. The novel characteristics of the invention is the introduction of a corresponding matrix of water rods (cylindrical rods with liquid phase water flow) positioned between the fuel rods, as opposed to the current practice of using or displacing a subset of fuel rods with large central water rod(s) for this purpose.

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

Abstract: A fuel bundle for a natural-circulation boiling-water reactor includes at least one coolant bypass tube which is at least partially open at both its top and bottom and extends about 2/3 of the bundle height. Water within the bypass tube remains liquid. As it exits the top of the bypass tubes, it merges with and "cools" the flow exterior to the tube. This arrangement reduces the pressure drop across the core, increasing coolant flow. In addition, the merging coolant helps improve heat transfer at the maximum heat flux levels within the core. Lateral holes through the bypass tube can further enhance with heat transfer distribution in the core. The reduced pressure drop in the core and the more uniform heat flux distribution both permit a reactor to operate at higher power ratings.

Abstract: Water rod configurations, such as for a boiling water nuclear reactor, are provided. An efficiency parameter is defined which relate to how well-used the sacrificed fuel rod positions are. Four particular water rod configurations are described, which produce high efficiency, such as having a water rod efficiency greater than about 0.6, preferably greater than about 0.7. Desired moderation is achieved by providing for sacrifice of more than four and less than nine lattice positions. The first "peanut" configuration has a cross-section with two round-cornered triangular regions, integrally connected by a constricted portion. The second configuration has a substantially rectangular cross-section. The third "clover" configuration has a four-lobed shape. The fourth "figure 8" configuration has two substantially circular cross-sectional portions. A method for analysis and design, using a new efficiency parameter, is provided.

Abstract: A fuel assembly for a boiling water reactor includes an elongated case having an interior and inner surfaces. A base part has inlet openings discharging into the interior of the case for coolant flowing in a given flow direction and a head part has outlet openings leading out of the interior of the case for the coolant flowing in the given flow direction. Mutually parallel fuel rods containing nuclear fuel are disposed in the case between the base and head parts. The inner surfaces of the case have a profile with a rectilinear alignment as seen in the given flow direction and flow trippers extending transversely to the alignment in the form of bulges protruding inward in the given flow direction. Each of the bulges has a sloped surface facing toward the coolant with an impact surface substantially perpendicular to the given flow direction.

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: 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 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: 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.