Abstract: Separation devices are disposed in the vent volume above part-length rods and above one or more of the spacers above the upper ends of the part-length rods. The separation devices preferably comprise swirlers located above the lattice openings which would otherwise receive the rods but for the underlying part-length rods. In this manner, flow is directed laterally outwardly onto the surfaces and into the interstices of the full-length fuel rods for improved power performance while simultaneously adverse pressure drops across the spacers are minimized.

Abstract: A nuclear fuel bundle has full-length and part-length fuel rods, the latter defining vent volumes interspersed among the full-length fuel rods. The vent volumes afford critical power enhancement by efficiently transferring liquid to adjacent full-length fuel rods. Except for full-length fuel rods adjacent unheated surfaces, for example, the channel and water rods, each fuel rod lies face adjacent a steam vent volume and full-length fuel rods diagonally adjacent a steam vent volume lie face adjacent at least one other steam vent volume whereby, except for full-length fuel rods adjacent non-heat generating surfaces, enhanced critical power performance is applicable to all full-length fuel rods notwithstanding diagonal location of full-length fuel rods relative to a steam vent volume.

Abstract: A steam/water separating device for a nuclear fuel bundle is located in a vent volume above part-length rods and includes a helical swirl vane. In one form, the swirl device lies below a vent tube and a transition element for flowing liquid laterally outwardly into the interstices of the fuel rods and steam upwardly within the vent tube. In another form, the vane depends from a cylindrical barrel open at its lower end. An annular pick-off tube extends into the open upper end of the barrel and lies in communication through a transition element with a superposed steam vent tube. An annular outlet is defined between the barrel and pick-off tube and the transition element deflects coolant water flowing through the annular outlet in a lateral outward direction for flow into the interstices of and onto the full-length fuel rods. Steam flows upwardly in the barrel through the pick-off tube into the steam vent tube.

Abstract: A lower tie plate includes a lower, generally cylindrically shaped nozzle for communicating coolant through a transition section of the tie plate to a grid at the upper end of the lower tie plate. The transition section is in the geometric form of a truncated, inverted pyramid, with flat side walls intersecting the cylindrical nozzle and the undersurface of the square grid. In this manner, minimum pressure loss is achieved by the flow from the nozzle to the grid. A shaped body diverter, i.e., an inverted pyramid, may depend from the grid to divert the flow laterally with minimum pressure loss into regions where the flow is most needed in the fuel bundle, i.e., in and about the fuel rods rather than the water rods. The inverted solid may have coolant flow passages through the solid to direct the flow into registering openings in the grid.

Abstract: A deflector is disposed in a steam vent region above the upper ends of part-length fuel rods to deflect upwardly flowing liquid laterally outwardly into the interstices of the full-length fuel rods adjacent the steam vent region. The deflector is supported by a spacer or from the upper tie plate and can be removed from the fuel bundle for access to the part-length fuel rods. The deflector may comprise a flat plate, an inverted pyramid, an inverted cone, a multi-sided pyramidal configuration or a swirl device wherein the horizontally projected area of the deflector is substantially coextensive with the horizontal cross-sectional area of the steam vent area. In this manner, a higher density liquid is provided in the interstices of the full-length rods while the lower density steam flows into the steam vent volume for flow upwardly out of the fuel bundle.

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

Abstract: 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: Apparatus is provided for simulating a nuclear fuel rod bundle transient condition and includes a vessel for containing a coolant, a pair of heating elements disposed in the vessel and a power supply for supplying power over time to each of the heating elements. The power supply is independently controlled whereby a variable supply of power over time to each heating element is provided, thus simulating the variation in power output and axial flux shape in a nuclear fuel bundle as a function of time.

Abstract: A spacer for retaining nuclear fuel rods in laterally spaced relation to one another includes first and second sets of spacer strips extending in mutually perpendicular diagonal directions relative to a generally rectilinear peripheral spacer band. The strips have linearly extending sections with adjacent sections angularly related to one another and meeting at apices. The sections of each strip alternately intersect a diagonal line across the spacer with the apices alternately located on opposite sides of the diagonal line. Alternate apices have springs projecting to one side of the strip for engaging fuel rods and apices between the alternate apices have stops projecting on opposite sides of the strip for engaging the fuel rods. Slots are provided in the strips enabling intermeshing of the strips with one another to define discrete cells peripherally encompassing and retaining fuel rods within the spacer.

Abstract: The lower tie plate grid includes cylindrical bosses and webs interconnecting the bosses for supporting nuclear fuel rods and defining flow channels through the grid for flowing coolant upwardly about the fuel rods. The grid includes shaped body members having flow openings, the members being disposed in each of the flow channels. In one form, the members define with the side walls of the bosses and webs a debris retention zone. In another form, sets of generally parallel, laterally spaced bars are disposed at discrete elevations in the flow channels. The bars are orthogonally related to one another whereby the effective debris catching area is defined by the openings through the crossed bars in plan, while the coolant flow area comprises essentially the space between each set of bars.

Abstract: A spacer for use with a fuel bundle in a nuclear reactor includes a matrix of ferrules for surrounding individual fuel rods within a bundle; a band surrounding the matrix and defining a peripheral wall of the spacer, the band having an upper edge; and a plurality of laterally spaced flow tabs extending upwardly from the upper edge, each flow tab having a lower substantially vertical portion and an upper inclined portion extending away from the vertical portion. The vertical portion and the inclined portion are formed with centrally located creases which define reverse bends in the upper and lower portions of the tab.

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

Abstract: A unitary one-piece lower tie plate grid has a lower portion and an upper portion for supporting the fuel rods. The lower tie plate grid includes cylindrical boss portions extending upwardly from the lower grid portion and arranged in square matrices for receiving the lower end plugs of the fuel rods. Web portions extending upwardly from the lower tie plate portion interconnect the boss portions along the sides of the matrices. The lower grid portion includes a plurality of openings which open into the flow spaces defined by the convex portions of the bosses and the webs within each square matrix of the upper portion of the tie plate. Coolant flows through the openings into the flow spaces for further flow upwardly about the fuel rods. The openings are radiussed adjacent their lower ends and have divergent side walls downstream of a throat area to define a flow venturi.

Abstract: In a boiling water reactor fuel bundle, a three dimensional debris catching grid construction is placed within the flow volume defined by the lower tie plate assembly between the inlet nozzle and upper fuel rod supporting grid. A perforated plate is utilized having round holes as small consistent with the prevention of inadvertent closure due crudding and a hole pitch consistent with mechanical integrity requirements. The perforated plate is placed in a three dimensional construction such as a dome, cylinder, pyramid, inverted pyramid or corrugated construction spanning the flow volume of the lower tie plate assembly. As a consequence of this three dimensional grid construction, the total flow through area of the perforations in the metal plate does not introduce appreciable pressure drop in the lower tie plate assembly between the inlet nozzle and the rod supporting grid.

Abstract: A fuel bundle and lower tie plate assembly for a nuclear reactor includes a plurality of fuel rods supported between an upper tie plate and a lower tie plate assembly, the lower tie plate assembly including an upper grid portion and a lower body portion, the upper grid portion having a plurality of fuel rod supporting bosses interconnected by a plurality of webs thus forming flow openings between the bosses. The body portion includes an inlet nozzle and a peripheral wall extending between the bottom nozzle and the upper grid portion to define a flow volume therein. A debris catcher, including a plurality of perforated tubes, is incorporated into the lower tie plate assembly, such that one of the tubes is in abutment with a respective lowermost end of each of the plurality of fuel rod supporting bosses.

Abstract: In a fuel bundle for use in the core of a boiling water nuclear reactor, part length rods having a tendency to reduce pressure drop are used in combination with spacers and spacer attached devices tending to utilize pressure drop to improve critical power. The addition of the part length rods has the advantage of lowering the pressure drop. Attached devices substantially increase the pressure drop. Exemplary spacer attached mechanisms for the utilization of pressure drop are set forth including vanes--preferably swirl vanes on the spacers, decreasing the spacer pitch to increase the total number of spacers in the upper two phase region of the fuel bundle, increasing the vertical height of the spacers, and increasing the thickness of the metal from which the spacers are constructed. Two classes of separation devices are disclosed for placement in the volume overlying the end of the partial length fuel rods.

Abstract: In a boiling water nuclear reactor fuel bundle, a debris catching arrangement is disclosed for incorporation within the flow plenum up stream or below the rod supporting grid of the lower tie plate assembly. The device is preferably placed within the lower tie plate flow plenum between the fuel bundle inlet and the rod supporting grid structure supporting the fuel rods; alternate placement can include any inlet channel upstream of the fuel rods including the fuel support casting. The disclosed debris catching designs include strainer structures defining spatially separated straining or obstructing layers imparting to the fluid in the plenum a circuitous flow path. This circuitous flow path causes the two phase separation of the heavier debris from the lighter transporting water by flow direction change with the debris directed and detoured to a trapping structure.

Abstract: In a boiling water reactor fuel bundle, a three dimensional debris catching grid construction is placed within the flow volume defined by the lower tie plate assembly between the inlet nozzle and upper fuel rod supporting grid. A perforated plate is utilized having round holes as small consistent with the prevention of inadvertent closure due crudding and a hole pitch consistent with mechanical integrity requirements. The perforated plate is placed in a three dimensional construction such as a dome, cylinder, pyramid, inverted pyramid or corrugated construction spanning the flow volume of the lower tie plate assembly. As a consequence of this three dimensional grid construction, the total flow through area of the perforations in the metal plate does not introduce appreciable pressure drop in the lower tie plate assembly between the inlet nozzle and the rod supporting grid.

Abstract: A spacer array is disclosed in which alternating cells are disposed at differing elevations. In a preferred octagonal spacer cell array, alternate fuel rods within the rows and columns of the fuel bundle matrix are surrounded by octagonal spacer cells at a first elevation. Likewise, and in the same preferred octagonal spacer array, the remaining alternate fuel rods within the rows and columns of the fuel bundle matrix are surrounded by octagonal spacer cells at a second elevation. The octagonal spacer cells of the spacer array at one level adjoin the octagonal spacer cells of the spacer array at an adjacent level. Specifically, each octagonal spacer cell has the top and/or the bottom of as many as four of its eight sides disposed for joinding with one side of as many as four octagonal cells in an adjacent cell layer. Each cell has approximately 0.6 of an inch height, or one-half the 1.2 inch height of the prior art.

Abstract: In a boiling water nuclear reactor fuel bundle, the use of a shortened ferrule spacer in combination with overlying swirl vanes is set forth. In the preferred embodiment, the shortened ferrule spacer is placed under any swirl vanes and has an individual ferrule surrounding each fuel rod at the elevation of the spacer. Each ferrule is given both minimum side wall thickness in the range of 0.020 inches or less as well as reduced height in the order of 0.9 inch or less. The reduced height and thickness of the ferrule spacer is required to maintain pressure drop within acceptable limits and still tends to augment the required liquid film for steam generation over the fuel rod lengths downstream (that is immediately above) the spacer. At the same time, the swirl vane structure is placed immediately above the ferrule spacer overlying the so-called subchannel region of the ferrule spacer between the fuel rods.