Abstract: A nuclear reactor core has a first group of fuel rods containing fissionable material and no burnable absorber, and a second group of fuel rods containing fissionable material and two burnable absorber materials. The groups of fuel rods are arranged in the core for controlling power peaking and moderator temperature coefficient. The number of fuel rods in the first group are greater than the number in the second group. The two burnable absorber materials can be provided as separate coatings or a mixture. One burnable absorber material is an erbium-bearing material such as erbium oxide and the other is a boron-bearing material such as zirconium diboride. Alternatively, the erbium-bearing material can be interspersed or mixed with the fissionable material.

Abstract: A nuclear fuel body provided by doped uranium dioxide grains having kernels of undoped uranium dioxide. The body is produced by mixing single crystal seeds of uranium dioxide with doped uranium dioxide granules. The mixture is compacted and subsequently sintered. Gadolinia is a preferred dopant for the uranium dioxide.

Abstract: A fuel assembly has a plurality of first fuel rods each of which contains nuclear fuel material but does not contain burnable poison, and a plurality of second fuel rods each of which includes nuclear fuel material and burnable poison. The amount of burnable poison in a lower region of the fuel assembly is smaller than that in an upper region thereof. When each of the second fuel rods is divided into an upper region and a lower region, a region of the divided regions in the second fuel rods containing a maximum burnable poison concentration Gmax and a region of the divided regions in the second fuel rods containing a minimum burnable poison concentration Gmin are located in the lower region of the fuel assembly. The burnable poison concentration of the upper region of each second fuel rod is between Gmax and Gmin. The fuel assembly may moderate a maximum linear heat rating with an increased spectral shift effect.

Abstract: The disclosed invention consists of a ceramic form of fuel for a nuclear reactor comprising an oxide of a fissionable element and containing therein a consumable neutron absorbing agent. The ceramic fissionable fuel product provides longer fuel performance in nuclear reactor service.

Abstract: A fuel element for a nuclear reactor having a zirconium-tin alloy cladding tube, with a thin coating of particles of enriched boron-containing compound burnable poison particles, deposited from a liquid sol-gel which includes a glass binder material.

Abstract: A fuel assembly for use in a boiling water reactor has a multiplicity of fuel rods. In the fuel assembly, among the fuel rods located in the periphery (for example, the outermost periphery) of the cross section of the fuel assembly, the proportion of fuel rods whose enrichment in their respective lower regions are greater than the average enrichment in the lower region of the fuel assembly is less than the proportion of fuel rods whose enrichment in their respective upper regions are greater than the average enrichment in the upper region of the fuel assembly.

Abstract: A fuel assembly for a nuclear reactor includes a number of fuel rods filled with a fuel material. A water rod having a cross sectional area larger than that of each fuel rod is disposed at substantially the central portion of the fuel assembly. The fuel rods include first fuel rods having a whole effective fuel zone filled with a fuel material throughout the entire length thereof and second fuel rods each having an interposed zone in which enrichment of a fissile nuclide is significantly reduced or the fissile nuclide does not exist at all. The second fuel rods are arranged so as to surround the water rod so that the interposed zones are positioned on an axial level including a portion at which subcriticality is made small at a period in which maintenance of reactor shut-down margine is made difficult during the reactor operation period.

Abstract: Fuel element rod for a pressurized water-cooled nuclear reactor having a cylindrical can (2) made from an alloy which is transparent to neutrons and closed at each of its ends by a plug (3, 4), namely an upper plug (3) and a lower plug (4) and having a first portion in which are stacked fuel material pellets (6), which is optionally inserted between two insulating pellets (7, 8), and a second portion or expansion chamber (5) containing a compressed spring (9) bearing at one end on the upper plug (3) and at the other end on the stack of fuel pellets (6) which it maintains in position, characterized in that the spring is made from hafnium.

Abstract: The fuel element comprises a plurality of modular capsules (5) arranged in sequence axially within a sheath (2). Each of the capsules (5) comprises a tubular case (10) closed at both ends by a porous element (13, 14) and enclosing a stack of pellets (11) in contact with the inner surface of the case (10) without radial clearance. The outside diameter of the capsules (5) is such that a very small radial clearance exists between the outer surface of the capsule (5) and the inner surface of the sheath (2).

Abstract: A fuel element for a nuclear reactor having a zirconium tin alloy cladding tube, with a thin coating of enriched boron-containing alloy burnable poison, such as nickel-thallium-boron deposited from a reducing agent by an electroless plating process.

Abstract: A radiation shielding material for intercepting not only .gamma. rays and x rays but also neutrons, comprising sulfur, iron oxide powder, lead oxide powder, gadolinium oxide powder and hydrogen-occluding alloy powder; and a process for preparing the radiation shielding material.

Abstract: A fuel assembly comprises a channel box, upper and lower tie plates fixed to the upper and lower portion of the channel box and a bundle of fuel rods enclosed in the channel box and retained by the upper and lower tie plates. The bundle of fuel rods includes ordinary fuel rods containing fissile material not containing gadolinia, and gadolinia-containing rods each containing gadolinia therein and having a larger outer diameter than that of the ordinary fuel rod. The gadolinia-containing rod has pellets enclosed in a closed cladding, and the outer diameters of the pellets also are larger than these of fuel pellets of the ordinary fuel rods.

Abstract: A fuel element for a nuclear reactor having a zirconium-tin alloy cladding tube, with a thin coating of particles of enriched boron-containing compound burnable poison particles, such as ZrB.sub.2 deposited from a liquid suspension which includes an acrylic polymer binder material and isopropanol. Graphite lubricant particles can be included in the coating.

Abstract: A nuclear fuel assembly comprising a plurality of fuel rods, each fuel rod comprising a cladding tube closed at both ends and filled with cylindrical nuclear fuel pellets such as sintered uranium dioxide or uranium plutonium dioxide. All or nearly all of the cylindrical pellets are coated with a refractory boride coating of sufficient thickness to prevent mechanical interaction between the pellets and the tube. The isotopic composition of the boron in the refractory boride is adjusted for each batch of fuel pellets, rods, or assemblage of rods so that the initial excess reactivity, k, of the batch, when assembled in a reactor core, is nearly zero.

Abstract: A fuel assembly is composed of first fuel rods containing nuclear fuel material and burnable poison material and second fuel rods containing nuclear fuel material but no burnable poison material. The fuel assembly is charged in a high conversion area of a boiling water type nuclear reactor having a reactor core having the high conversion area and a burner area surrounding the high conversion area. A ratio V.sub.C /V.sub.F is not greater than 1.5 in the fuel assembly where V.sub.C is the volume occupied by coolant flow paths and V.sub.F is the volume occupied by the nuclear fuel material per unit length in an axial direction of the fuel assembly. In addition, the burnable poison material is composed of neutron absorption nuclides having at least one resonant energy in a neutron energy region of one electron volt or less.

Abstract: Nuclear fuel elements are provided that are resistant to pellet-clad interaction. The closed end nuclear fuel elements comprise a zirconium or zirconium alloy tube that has a layer of lubricant, preferably graphite, on the inner surface thereof, and enriched uranium dioxide pellets that have a coating on the outer surface thereof of a thickness sufficient to absorb fission products. The coating on the pellets may be a burnable absorber or a material that has a relatively low neutron absorption compared to a burnable absorber. The combination of the layer on the tube and the coating on the pellets reduces both the stress level and the concentration of damaging fission products that would contact and react with the layer of lubricant about the inside surface of the tubular cladding and thus reduces conditions for pellet-clad interaction.

Abstract: A sintered nuclear fuel compact of UO.sub.2 or the mixed oxides (U, Pu)O.sub.2 and (U, Th)O.sub.2, with which reactivity losses in a nuclear reactor having relatively long fuel element cycles are avoided, has in its sintered matrix neutron poison in the chemical compound form UB.sub.x with x=2; 4 and/or 12 and/or B.sub.4 C. A sintered nuclear fuel compact of this kind is produced by sintering from a compact comprising a mixture of at least one of the mixture components UO.sub.2, PuO.sub.2, (U, Pu)O.sub.2 and (U, Th)O.sub.2 powder with UB.sub.x powder, where x=2; 4 and/or 12 and/or B.sub.4 C powder.

Abstract: A process for forming a boron-containing coating on the internal surface of a zirconium or zirconium alloy hollow tube by heating the internal surface to a temperature of between 200.degree.-450.degree. C. and passing through the tube a mixture of a volatilized boron compound in helium or argon, such that the boron compound decomposes to form an integral boron containing coating on the internal surface.

Abstract: Sintered nuclear fuel bodies are manufactured by pressing a powder of UO.sub.2 containing 1-20 percent by weight Gd.sub.2 O.sub.3 and up to 20 percent by weight U.sub.3 O.sub.8 into a pressed body and sintering the pressed body, the Gd.sub.2 O.sub.3 at least partly consisting of monoclinic Gd.sub.2 O.sub.3. The monoclinic Gd.sub.2 O.sub.3 used can be manufactured by heat treatment of cubic Gd.sub.2 O.sub.3 at a temperature of at least 1250.degree. C. By employing monoclinic Gd.sub.2 O.sub.3 a considerably increased homogeneity with respect to solid solution of gadolinium in the UO.sub.2 structure is obtained. Particularly favorable results are obtained if the sintering is carried out in a sintering atmosphere which, at 1750.degree. C., has an oxygen partial pressure which is higher than 10.sup.-7 atm.

Abstract: A neutron-absorbing material is formed by a process which includes the steps of: mixing an absorptive material having a high thermal neutron capture cross-section (e.g., B.sub.4 C), a neutron-moderating material (e.g., graphite) and a binder (e.g., a phenol formaldehyde resin); shaping such mixture; curing such shaped mixture (e.g., to complete polymerization of the resin and to have only a carbon residue); and siliconizing such shaped and cured mixture. The resulting product has been formed to be denser and stronger, and more oxidation- and abrasion-resistant than prior art compositions.

Abstract: A nuclear fuel rod cladding having a burnable absorber integrally incorporated therein has an outer tubular layer of a zirconium alloy; an intermediate layer, of a thickness less than the outer tubular layer, of a zirconium alloy containing a boron-containing burnable absorber; and an inner layer, of a thickness less than the intermediate layer, of zirconium metal. The layers are bonded together to form a cladding for the containment of nuclear fuel.

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

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

Abstract: A process for forming a boron-containing coating on the internal surface of a zirconium or zirconium alloy hollow tube by heating the internal surface to a temperature of between 200.degree.-450.degree. C. and passing through the tube a mixture of a volatilized boron compound in helium or argon, such that the boron compound decomposes to form an integral boron containing coating on the internal surface.

Abstract: A fuel assembly having a plurality of fuel rods arranged in a lattice state and being charged into a core of a nuclear reactor using light water as a coolant, which comprises the fuel rods consisting of a first group of fuel rods and a second group of fuel rods, an average concentration of U.sup.236 in the first group being lower than an average concentration of U.sup.236 in the second group, and the first group and the second group being arranged unevenly in the fuel assembly, preferably, a fuel assembly wherein the first group is arranged at the periphery of the fuel assembly, and the second group being arranged at positions other than the periphery, has a low reactivity penalty due to U.sup.236 and can reduce the requirements for natural uranium.

Abstract: A cadmium oxide glazed nuclear fuel pellet and glazing composition therefor is disclosed which controls the reactivity and extends the operating life cycle of a nuclear reactor while increasing the rate of burnout of the burnable absorber and reducing the amount of undersirable gases produced therefrom. The glaze forming composition comprises at least about 0.5 percent by weight cadmium oxide as a burnable absorber, i.e., cadmium-113 isotope, and at least one glaze forming oxide. The glaze constituents are formed into a slurry and a nuclear fuel pellet is dipped into the slurry to produce a hard refractory glaze upon firing and cooling.

Abstract: A nuclear fuel assembly has a plurality of fuel rods each containing a multiplicity of fuel pellets. The fuel rods include a plurality of first fuel rods and a plurality of second fuel rods. Each of the first fuel rods contains a burnable poison over substantially the entire axial length thereof. The first fuel rod also has a greater means enrichment in the upper axial region thereof than that in the lower axial region thereof. Each of the second fuel rods contains no burnable poison and has a uniform enrichment distribution over substantially the entire axial length thereof. In each cross-section of the fuel assembly perpendicular to the axis thereof, the outer peripheral portion has a greater mean enrichment than the central portion. The first fuel rods are disposed in the peripheral portion except the outermost peripheral portion of the cross-section of the fuel assembly.

Abstract: A burnable absorber-containing glaze is formed on nuclear fuel pellets by applying a finely divided mixture of a boron-containing burnable absorber and a boron-containing glass to the pellet surface as a coating and firing the coated pellets at 900.degree.-1100.degree. C., for about 5 to 15 minutes, to melt the boron-containing glass and encapsulate the boron-containing burnable absorber. The coating is of a thickness of 1 mil or less and contains an amount of B.sup.10 sufficient to provide desired absorption of neutrons during reactor operation. The resultant pellets exhibit good adhesion of the coating and excellent resistance to moisture adsorption.

Abstract: A method of operating a gas-cooled nuclear reactor having graphite fuel elements in which, to reduce the reactor, a quenching element is introduced which takes a particle of a reaction-reducing substance in a sheath which will melt or release the substance in vapor form so that the substance can penetrate in gaseous form through the surrounding graphite body and deposit upon fuel elements.

Abstract: The present invention relates to a nuclear fuel pellet having two sections: a cylindrical inner pellet inside of an annular outer pellet. The inner pellet is composed of gadolinia and natural or depleted uranium as UO.sub.2. The outer pellet contains enriched uranium as UO.sub.2 but without gadolinia.

Abstract: UO.sub.2 base powder exhibiting any specific surface and crystallite diameter properties is mixed with rare earth (SE) oxide-containing powder, the particles of which exhibit at least in one surface layer, a crystal lattice of the fluorite type, with the stoichiometric composition (SE.sub.0.5, U.sub.0.5) 0.sub.2.00 and/or form it in sintering; and is compacted to form compacts which are sintered in a gas atmosphere with reducing action at 1500.degree. C. to 1750.degree. C. to form high-density sintered bodies.

Abstract: A nuclear fuel rod contains nuclear fuel pellets that have incorporated therein a hybrid burnable absorber that affects a moderation of the burn-out rate of the system containing the rod. The nuclear fuel pellets contain 1 to 20 percent by weight gadolinium oxide and 0.02 to 1.0 percent by weight of boron carbide particles of a size between 20 to 100 microns in diameter, the particles coated with a 0.5 to 10 micron thick coating of a helium gas-impervious coating.

Abstract: Substantially isotropic spherical fuel and absorber elements for high temperature reactors are produced by molding corresponding fuel particles and graphite molding compositions. There is used as graphite molding powder a mixture of graphitized granules of coke and a hardenable resin binder. There are first produced in steel dies at 80.degree. to 120.degree. C. half shells and a nucleus with a pressed density of 1.0 to 1.4 g/cm.sup.3 followed by molding in a further steel die to the final format.

Abstract: A fuel pellet for a nuclear core fuel rod for use in a nuclear reactor fuel assembly having a predetermined radial distribution of burnable poison, fertile, and fissile nuclear material to provide the desired control of reactivity of the fuel pellet with the minimum amount of burnable poison material and to provide control of the nuclear reactivity of the fuel assembly.

Abstract: A sputter coating apparatus target includes an elongated cathode having an upper support surface, sputter target material disposed upon the upper cathode surface, and a ground shield having a box-like construction. The ground shield includes a bottom wall and side walls containing the cathode therein in an enclosed state and an open top defined by the side walls adjacent to the upper cathode surface placing the target material in an exposed state. Also, blocks are provided for supporting the cathode within the shield in a spaced electrically insulated relationship relative to the shield such that a gap is defined between the cathode and the bottom and side walls of the shield.

Abstract: The invention provides a fuel assembly comprising a plurality of fuel rods containing a fissionable material and a plurality of moderator rods filled with a burnable poison and a metal hydride as a solid moderator material. All of the burnable poison in the fuel assembly is filled in the moderator rods, and number of the moderator rods is at least 4 and not more than 15% of total number of the fuel rods and the moderator rods.

Abstract: The nuclear fuel assembly comprises a bundle of fuel elements some of which contain a burnable neutronic poison, held in position at the nodes of a regular lattice by a skeleton having end pieces connected together by guide tubes occupying some of the nodes of the lattice. All the poison-containing elements are disposed so as to act on the reactivity of the adjacent assemblies in the heart of the reactor.

Abstract: An improved nuclear fuel rod comprising a tubular metallic cladding containing a plurality of nuclear fuel pellets has a plurality of ceramic wafers therein, each of which wafers being disposed between a major portion of adjacent fuel pellets. The ceramic wafers are formed from a sintered mixture of natural or depleted uranium dioxide and 1-8 percent by weight gadolinium oxide. The wafers are of a diameter substantially the same as that of the fuel pellets and have a thickness of between 10-100 mils. The wafers freeze out harmful fission products released by the fuel pellets and minimize or prevent pellet-clad interaction failures, while also providing flexibility in power shaping in the reactor system.

Abstract: A reactor fuel assembly (15) configuration which allows cold shutdown margins to be met with minimal penalty to operating efficiency. The assembly comprises a component of fissile material distributed over a substantial axial extent of the fuel assembly and a component of neutron absorbing material having an axial distribution characterized by an enhancement in a relatively short axial zone (65) (the "cold shutdown control zone") corresponding to at least a portion of the axial region of cold shutdown maximum reactivity. The axial distribution of the component of neutron absorbing material typically is characterized by an additional enhancement in an axial zone (62) (the "hot operating control zone"). The component of neutron absorbing material is conveniently incorporated into at least some of the fuel rods (57-G1, G2, G3, G4). The enhancement in the cold shutdown control zone may be provided at least in part by one or more fuel rods (G2, G3) having absorber only in the cold shutdown control zone.

Abstract: A method and apparatus for vaporizing any flakes of sputtering target material which short circuit high voltage cathodes during the sputtering of a coating on a substrate such as nuclear fuel pellet positioned in the vacuum chamber of a sputtering device. A separate low voltage, high current auxiliary power source is used to evaporate the shorting flakes. The present method and apparatus reduces the process recovery time in the event of a shorting flake from as long as 6 hours down to as little as 5 minutes without compromising the purity of the sputtered coating. The auxiliary power source may be an ac source which is preferably connected in series with the shorting flake so that current from the ac source will cease as soon as the shorting flake is evaporated. A ballast and/or short circuit indicating device may also be provided in series with the ac source in order to limit the ac current and in order to indicate the presence of shorting flakes.

Abstract: A fuel assembly for loading in the core of a boiling water reactor comprises a large number of vertically extending fuel rods, some of which contains a burnable poison, where a rod-average uranium enrichment of fuel is higher in the upper region of the fuel assembly than in the lower region and a total content of the burnable poison is lower in the lower region of the fuel assembly than in the upper region and a spectral shift effect of the boiling water reactor is increased while thoroughly maintaining a reactor shutdown margin, and a discharge exposure is increased.

Abstract: A burnable absorber coated nuclear fuel. A fissionable material nuclear fuel substrate is at least partially covered by a burnable absorber layer. A hydrophobic material overcoat layer generally covers the burnable absorber layer and is bonded directly to it.

Abstract: A method for coating a nuclear fuel with a burnable poison and a burnable poison coated nuclear fuel made by the method. The nuclear fuel is surface cleaned, and then a burnable poison layer is sputtered thereon. A sputtering deposition rate is picked that preferably will heat the nuclear fuel surface between 200.degree. C. and 600.degree. C. For deposition rates that result in heating the nuclear fuel surface to less than 200.degree. C., external heat is applied to heat the nuclear fuel surface between 200.degree. C. and 600.degree. C. To make the burnable poison layer less hygroscopic, an overcoat layer of a hydrophobic material is sputtered on the burnable poison layer.

Abstract: A method for coating a uranium dioxide nuclear fuel with a zirconium diboride burnable poison. First, a layer of niobium is bonded to the nuclear fuel. Then, a layer of zirconium diboride is deposited by chemical vapor deposition on the niobium layer. A zirconium diboride coated nuclear fuel having a layer of niobium between a uranium dioxide substrate and the zirconium diboride layer also is disclosed.

Abstract: Apparatus for depositing a coating (such as a burnable absorber) on nuclear fuel pellets. Pallets 16 hold a single layer of fuel pellets 22 between lower and upper screened parts 18 and 20. A rotating drum 14 holds the pallets 16 on its circumference. A chamber 12 encloses the drum 14. A sputtering machine 24 has stationary, sputter-frangible, upper and lower targets (such as zirconium diboride) 26 and 28. The stationary upper targets 26 are placed inside the drum's circumference above its longitudinal axis and are pointed facing generally upward and radially outward. The stationary lower targets 28 are placed outside the drum's circumference below its longitudinal axis and are pointed facing generally upward and radially inward. The target material is sputtered onto the fuel pellets 22 as the pallets 16 on the drum 14 rotate past.

Abstract: A method of applying a burnable absorber coating on a nuclear fuel pellet comprising the step of exposing the nuclear fuel pellet to a gas stream of boron trichloride and anhydrous ammonia at a temperature of from about 600.degree.-800.degree. C. A coating of boron nitride is formed as a reaction product of boron trichloride with anhydrous ammonia on the fuel pellet.

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

Abstract: An improved annular burnable poison pellet of aluminum oxide-boron carbide (Al.sub.2 O.sub.3 --B.sub.4 C) adapted for positioning in the annular space of concentrically disposed zircaloy tubes. Each tubular pellet is fabricated from Al.sub.2 O.sub.3 powders of moderate sintering activity which serves as a matrix for B.sub.4 C medium size particle distrbution. Special pellet moisture controls are incorporated in the pellet for moisture stability and the pellet is sintered in the temperature range of 1630.degree.-1650.degree. C. This method of fabrication produces a pellet about 2 inch long with a wall thickness of about 0.020 inch to 0.040 inch. Fabricating each pellet to about 70% theoretical density gives an optimum compromise between fabricability, microstructure, strength and moisture absorption.

Abstract: A core construction for a nuclear reactor having a multiplicity of fuel cells forming a core in which each fuel cell includes four fuel assemblies arranged in adjacent relationship and one control rod insertable into a position surrounded by the four fuel assemblies. The fuel cells includes first fuel cells each having a relatively high cell mean infinite neutron multiplication factor and including one fuel assembly containing a burnable poison, and second fuel cells each having a relatively low cell mean infinite neutron multiplication factor and including no fuel assembly containing a burnable poison. The first fuel cells are arranged both in a central zone of the core disposed within about one-half the core radius from the center of the core and in a circumferential zone of the core outside the central zone. The second fuel cells are arranged only in the central zone and no second fuel cells are arranged in the circumferential zone.

Abstract: First nuclear fuel elements in which a fissionable material in which a burnable poison is incorporated is loaded and second nuclear fuel elements in which a fissionable material in which no burnable poison is incorporated is loaded are disposed in a nuclear fuel assembly. Content of the fissionable material in the first nuclear fuel element is less than about 72% of that of the fissionable material in the second nuclear fuel element adjacent to the first nuclear fuel element.