Abstract: The mechanical spectral shift reactor comprises apparatus for inserting and withdrawing water displacer elements from the reactor core for selectively changing the water-moderator volume in the core thereby changing the reactivity of the core. The apparatus may include drive mechanisms for moving the displacer elements relative to the core and guide mechanisms for guiding the displacer rods through the reactor vessel. An array of tubes may be disposed between the guide mechanisms and the fuel assemblies for guidance and minimization of flow induced vibrations of the displacer elements.

Abstract: A reusable fastener device includes an attachment nut and a retainer housing mounted to the adapter plate of the fuel assembly top nozzle and removable with the top nozzle upon reconstitution of the fuel assembly. The attachment nut has a central tubular stem and upper and lower flanges connected to and extending radially outwardly from opposite ends of the stem. The stem is internally threaded for mating with the threaded upper end plug extension of the strucutural member. The upper flange of the nut has a conical-shaped lower surface and a periphery adapted for engagement in order to rotate the nut for threading onto and unthreading from the structural member extension between fastened and unfastened positions. The lower flange of the nut is in the form of a plurality of radial segments extending outwardly from the stem and angularly spaced from one another so as to define a plurality of cutouts therebetween which alternate with the segments.

Abstract: An improved water displacer rod includes an elongated hollow thin-walled tube with a pair of end plugs attached to opposite ends of the tube to hermetically seal the tube and a plurality of support pellets disposed in a stacked relationship within the tube. The pellets allow the thin-walled tube to be laterally flexible while still able to resist collapse due to high external pressure. Each pellet is preferably formed of a body having a hollow annular cross-sectional shape and a pair of end webs extends across and closing opposite ends of the body. The body defines a central void and the webs seal the void. Thus, when the pellets are stacked within the tube, each void is sealed individually one from the next. A double barrier is provided in the displacer rod by the hermetically sealed tube and the individually sealed pellets.

Abstract: A top nozzle subassembly having a hold-down device incorporated therewithin is provided for a nuclear reactor fuel assembly. The subassembly is slidably mounted on the upper ends of the control rod guide thimbles and is removably attached by internally threaded collars which threadably mate with external threads provided on the upper ends of the guide thimbles. Unthreading of the collars allows the subassembly to be removed from the fuel assembly to gain top access to the fuel rods within the fuel assembly. The invention also includes a special tool for threading and unthreading of the collars.

Abstract: The hold-down plate of the top nozzle of a fuel assembly is interconnected to the upper extension members of the fuel assembly guide thimbles by an improved joint structure associated with each of a plurality of passageways through the hold-down plate which receives an upper end portion of each one of the guide thimble upper extension members. The improved joint structure includes an internal annular ledge on the hold-down plate within the passageway at a lower portion thereof so as to surround the upper end portion of the extension member, an annular recess on the upper end portion of the extension member, and an annular spring member fitted on the upper end portion of the extension member within the recess.

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 structure disposed below the adapter plate of the bottom nozzle and between the corner legs of the nozzle. The structure is composed of a plurality of straps aligned with one another in a crisscross arrangement and defining a plurality of interconnected wall portions which form a multiplicity of small cells each having open opposite ends and a central channel for coolant flow through the trap. A plurality of spring-like fingers are punched out of the wall portions and bent to extend into the cell channels toward the downstream end of the trap structure to provide means to capture and retain pieces of debris carried through the channels by flowing coolant.

Abstract: An alignment sleeve capture arrangement in the top nozzle of a fuel assembly includes an internal cylindrical wall defining a bore through the upper hold-down plate of the top nozzle below and in communication with a passageway therein through which extends an alignment sleeve of the top nozzle which is used to attach it to the guide thimble of the fuel assembly. The bore has an inside diameter larger than the inside diameter of the passage so as to form a cavity surrounding an upper position of the alignment sleeve which extends axially through the bore as well as the passageway. Also, the arrangement includes an annular shoulder on the upper hold-down plate surrounding the alignment sleeve upper portion and defining an upper limit of the cavity. The shoulder forms a transition between the larger inside diameter of the bore and the smaller inside diameter of the passageway. Additionally, an annular retainer is attached to the upper hold-down plate and spaced below the shoulder.

Abstract: A fuel assembly for use at non-control rod locations of a nuclear reactor core includes top and bottom nozzles and longitudinal structural members extending between and attached to the nozzles for forming an integral unitary structure. One or more of the structural members includes an elongated hollow cladding tube extending between the top and bottom nozzles and end plugs secured to opposite ends of the tube for hermetically sealing and attaching the tube to the top and bottom nozzles. The improvements in the structural member relate to features for reducing fuel assembly bow. Such features relate to a quantity of thermal or irradiation-induced creep resistant material and pretensioning means positioned within the tube. The creep resistant material is a ceramic material in stacked pellet form and coated with a burnable adsorber material.

Abstract: In a reconstitutable fuel assembly, a top nozzle attaching structure for mounting the top nozzle adapter plate in releasable locking engagement upon the guide thimble upper end portions includes several improved features. First, a locking tube is mounted within the guide thimble upper end portion for movement between an upper locking position wherein the adapter plate and guide thimble upper end portion are maintained in the locking engagement and a lower unlocking position wherein the adapter plate is releasable from the guide thimble upper end portion. Also, a plurality of protrusions are attached on the locking tube so as to extend outwardly thereof and through axial slots defined in the guide thimble upper end portion. The protrusions are yieldable for engaging and releasing from a groove in the passageway of the adapter plate. The purpose of the adapter plate passageway groove is to receive a bulge on the guide thimble upper end portion when the guide thimble is engaged with the adapter plate.

Abstract: A fuel assembly with a top nozzle having an adapter plate, at least one guide thimble connected to the adapter plate, and a burnable absorber rod disposed within the guide thimble, includes a releasable latching structure for releasably interconnecting an end of the absorber rod to the adapter plate. The latching structure includes a recess defined in the adapter plate within a passageway through the plate, a mounting body attached to the end of the absorber rod and extending axially upward therefrom through the passageway and above the adapter plate, and a spring latch disposed about the mounting body above the adapter plate. The spring latch has circumferentially spaced latch fingers extending downwardly toward the adapter plate.

Abstract: An improved bottom nozzle of a fuel assembly includes a housing and a modified adapter plate formed by a network of ligaments which extend across the housing and are connected to the side walls of the housing a short distance below its upper peripheral edge so as to define an open region therein. The improved bottom nozzle also includes a debris trap having a structure disposed within the open region of the housing upon the adapter plate and adapted to capture and retain debris carried by collant flowing from openings in the lower core plate of the nuclear reactor to the fuel assembly. The trap structure is composed of a plurality of straps aligned with one another in a crisscross arrangement and defining a plurality of interconnected wall portions which form a multiplicity of small cells each having open opposite ends and a central channel for collant flow through the trap.

Abstract: A nuclear reactor in which control rods are inserted in the thimbles of only certain of the fuel assemblies (which may be called controlled assemblies) in the core and the remainder of the assemblies (which may be called non-controlled assemblies) are provided with hollow structural members containing burnable poison which form these non-controlled assemblies into integrated units. The hollow structural members are formed with end plugs welded to the lower end and are open at the top. The end plug of each member is secured to the bottom nozzle of the non-controlled fuel assembly. A skeleton is formed of the bottom nozzle, the structural members secured to it and a plurality of grids spaced along the structural members. A bulge tool is then inserted in each hollow member and it is on each side of each grid. Neutron absorbers are then inserted in each hollow member and an upper end plug is welded to it. The fuel rods are then inserted in the assembly and the upper end plugs are secured to the top nozzle.

Abstract: A secondary source positioning mechanism for a fuel assembly in a nuclear reactor locates an individual one of the secondary sources in a respective guide thimble of the fuel assembly aligned with an opening defined through the upper core plate which overlies the fuel assembly. The positioning mechanism has a tapered locating boss which registers with a chamfer on the lower side of the core plate about one of its openings and a resilient holddown device which resiliently couples the upper end of a rod containing the secondary source to the locating boss in a manner which restrains the upper end of the rod in the lateral direction and positions the secondary source rod in the axial direction.

Abstract: A method of straightening an irradiated fuel assembly having a plurality of control rod guide thimbles in which some of the guide thimbles are bowed and thus greater in length than other of the guide thimbles comprises the steps of determining the length adjustments required for shortening the respective bowed guide thimbles in order to make their respective lengths generally the same as the other guide thimbles, and then forming expansions in the bowed guide thimbles so as to shorten their respective lengths by the amounts of the length adjustments. Usually, a plurality of expansions are made in most of the bowed guide thimbles at spaced locations between opposite ends thereof. Some of the expansions differ in the amount of shortening from other of the expansions. Also, the total amount of shortening of the bowed guide thimbles is controlled by the number of the expansions and the amount of shortening which results from each expansion.

Abstract: An FM data receiver of the offset type, in which the local oscillator frequency is located between the two frequency-shift-keyed signalling frequencies. To counter the effects of drift in the local oscillator, a simple AFC system mixes the signalling tone signals with delayed signals to provide a frequency control signal.

Abstract: An improved top nozzle includes leaf spring assemblies interposed between its movable upper hold-down plate and stationary lower adapter plate and arranged along respective peripheries thereof. The leaf spring assemblies bias the upper hold-down plate in an upward direction into contact with the upper core plate of the reactor and thereby impose a hold-down force on the fuel assembly via the lower adapter plate. In the preferred embodiment, each leaf spring assembly includes opposite lower and upper ends, with the lower end being attached to the lower adapter plate adjacent one of the corners on its periphery and the upper end being movably coupled in a groove on the upper hold-down plate adjacent a next one of the corners on its periphery. The leaf spring assemblies are arranged in a single file about the peripheries of the lower adapter plate and upper hold-down plate, with one assembly extending between each pair of succeeding corners on the respective peripheries of the lower and uper plates.

Abstract: An improved top nozzle has an enclosure with a lower adapter plate and an upstanding sidewall surrounding and attached to the periphery thereof and an upper hold-down plate spaced above the adapter plate for abutmnet with a lower side of an upper core plate by a plurality of coil springs disposed between the lower and upper plates. The lower adapted plate and upper hold-down plate have respective openings and passageways defined therethrough in a pattern which matches that of the upper ends of the guide thimbles of the fuel assembly to which the improved top nozzle is attached. The upper ends of the guide thimbles extend upwardly through the adapter plate which is stationarily mounted on the guide thimbles. Tubular sleeves disposed between the lower and upper plates are surrounded by respective coil springs. The lower ends of the sleeves are releasably threaded to the upper ends of the guide thimbles, while the upper ends of the sleeves extend into the passageways of the upper hold-down plate.

Abstract: A non-boron moderator filled rod for a nuclear reactor fuel assembly has a tubular body with a pair of end plugs sealing the opposite ends thereof and defining a chamber within the body. A liquid moderator, such as light water, is contained witin the chamber. One of the end plugs acts as a hydride sink and a hydrogen getter sponge material is disposed adjacent the other end plug.

Abstract: A fuel assembly, particularly advantageous for use with a BWR, wherein the fuel bundle is adapted to be inserted into an envelope formed from a flow channel and a lower nozzle assembly. The fuel bundle is essentially axially symmetrical having identical top and bottom tie plates. Within the fuel bundle, alternate fission gas plenums are disposed at the top and bottom of the bundle respectively.During the refueling operation, the fuel bundle is removed from the reactor core, axially inverted and reinserted into the core for continued burn up. The invention takes advantage of the reactivity increase possible in a BWR when a partially burned fuel bundle is inverted.

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.