Abstract: In order to multiply by three or four the combustion level of nuclear fuel pellets in fast neutron nuclear reactors, it is proposed that following a normal irradiation period of said pellets in the reactor core, that the irradiated can be replaced by a new can with an internal diameter slightly exceeding that of the first can. Thus, the pellets can undergo a new irradiation cycle in the reactor core. Preferably, the can is destroyed by progressive local melting over its entire length and the new can is preheated to facilitate the introduction of the pellets.

Abstract: The improved fuel assembly has a plurality of elongated corner posts extending longitudinally between and releasably and rigidly interconnecting top and bottom nozzles so as to form a rigid structural skeleton of the fuel assembly. Additionally, a plurality of transverse grids are supported at axially spaced locations along the corner posts and a plurality of fuel rods are supported by the grids. Certain groups of the fuel rods are spaced apart laterally from one another by a greater distance than the rest of the fuel rods so as to define a number of elongated channels extending between the top and bottom nozzles. A cluster assembly having a cluster plate with a plurality of elongated rods is adapted to be removably supported on the top nozzle with its rods extending through the channels. The rods can be a plurality of guide thimbles in the case of one cluster assembly, or a plurality of oversized fuel rods in the case of another cluster assembly.

Abstract: For operating a PWR with spectral shift during all combustion cycles and with undermoderation during some cycles only, the reactor structure is designed for receiving either one of two types of fuel assemblies, having the same geometry. All fuel assemblies have guide tubes for receiving spectral shift clusters containing fissile material but with different elements bundles so as to be able to choose the type of operation.

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

Abstract: The universal fuel assembly has a plurality of elongated corner posts extending longitudinally between and releasably and rigidly interconnecting top and bottom nozzles so as to form a rigid structural skeleton of the fuel assembly. Additionally, a plurality of transverse grids are supported at axially spaced locations along the corner posts and a plurality of fuel rods are supported by the grids. Certain groups of the fuel rods are spaced apart laterally from one another by a greater distance than the rest of the fuel rods so as to define a number of elongated channels extending between the top and bottom nozzles. A cluster assembly having a cluster plate with a plurality of elongated rods is adapted to be removably supported on the top nozzle with its rods extending through the channels. The rods can be a plurality of guide thimbles in the case of one cluster assembly, or a plurality of oversized fuel rods in the case of another cluster assembly.

Abstract: Apparatus and process for supervising and controlling the operations of loading and unloading of fuel of a nuclear reactor comprising an information processor 30 formed from several units. A treatment unit 31 receives control signals giving notably the position, the speed, the load of machines 7 and 16 operating the loadings and unloadings of groups in the core 2, the reactor pool 3, and the spent fuel pit 14. A programmable unit 34 furnishes command signals, previously recorded, representing the loading sequence.

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 fusion blanket includes a chamber wall, a multiplication section, an enrichment section and a reflector in radially outward succession, respectively. The chamber wall isolates the fusion reaction chamber from the remainder of the blanket. Fusion neutrons bombard atoms in the multiplication section to free further neutrons which are then available for breeding fuel. The enrichment section contains fertile fuel of sufficient dilution to maximize the enrichment rate and minimize fast fission. Materials may be included in the multiplication section and the enrichment section to reduce thermal neutron flux, thereby suppressing thermal fission. Additionally, tritium may be bred in both sections. The fertile material is exposed to neutron bombardment until the desired enrichment is achieved. The particles may be removed and mixed to minimize nonuniformities in enrichment. The particles may then be fabricated into fuel elements for fission reactors.

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 method is disclosed for making a fuel pellet for a nuclear reactor. A mixture is prepared of PuO.sub.2 and UO.sub.2 powders, where the mixture contains at least about 30% PuO.sub.2, and where at least about 12% of the Pu is the Pu.sup.240 isotope. To this mixture is added about 0.3 to about 5% of a binder having a melting point of at least about 250.degree. F. The mixture is pressed to form a slug and the slug is granulated. Up to about 4.7% of a lubricant having a melting point of at least about 330.degree. F. is added to the granulated slug. Both the binder and the lubricant are selected from a group consisting of polyvinyl carboxylate, polyvinyl alcohol, naturally occurring high molecular weight cellulosic polymers, chemically modified high molecular weight cellulosic polymers, and mixtures thereof. The mixture is pressed to form a pellet and the pellet is sintered.

Abstract: A nuclear fuel assembly, particularly advantageous for use in a pressurized water reactor, wherein each alternate fuel rod in the assembly is positioned with its fission gas plenum zone at the top of the assembly and the intervening alternate fuel rods are positioned with their fission gas plenum zones at the bottom of the assembly. All of the fuel rods are preferably axially coextensive. An axial blanket region may be formed by providing the fuel zone of each fuel rod with a small zone of natural or depleted uranium at a part of the fuel zone furthest from the fission gas plenum zone. A method of effectively lengthening the active length of a nuclear fuel assembly is also described.

Abstract: A nuclear fuel assembly for high utilization of the nuclear fuel is disclosed. Alternate fuel rod assemblies are axially shifted relative to each other to create zones of high hydrogen-to-uranium ratios at the ends of the core for high utilization of the fuel at the core ends. Each fuel rod assembly comprises separate upper and lower fuel rods. The axial shift provides intermeshing of the separation between axially aligned fuel rods at the core center. Seed blankets are located at the ends of the core and lower enriched sections are located at the core center during beginning of core life. After a specified amount of fuel depletion from reactor operation, the upper and lower rods are interchanged and an opposite axial shift is employed. The high utilization fuel assembly provides for burnup gradient utilization, axial blanket utilization, plutonium production and burnup, axial power flattening, and less use of enriched uranium.

Abstract: An initial charge core of a fast breeder and a method of renewing fuel in the initial charge core. The initial charge core comprises a driver core region containing a fissile material, an external blanket region containing a fertile material and surrounding the driver core region, and an internal blanket region disposed within the driver core region and containing a fertile material. The axial thickness of the internal blanket region is greater at its central portion that at the peripheral portion thereof. The internal blanket region is enriched with the fissile material. The degree of enrichment in the internal blanket region is greater than that in the driver core region.

Abstract: A method for reducing thermal striping in liquid metal fast breeder reactors by reducing temperature gradients between adjacent fuel and blanket assemblies by shuffling blanket assemblies at each refueling outage so as to progressively shuffle the blanket assemblies to the core periphery through multiple moves and to generally locate fresh blanket assemblies adjacent to exposed fuel assemblies and exposed blanket assemblies adjacent to fresh fuel. Additionally, assembly orificing is altered to provide less flow to blanket assemblies needing less flow due to an otherwise decreased temperature gradient and providing additional flow to fuel assemblies which need more flow to sufficiently reduce temperature gradients to prevent thermal striping.

Abstract: An arrangement of square fuel assemblies in the first and subsequent cycles of a pressurized water nuclear reactor wherein shimmed feed assemblies and once-burned or equivalent assemblies occupy the same checkerboard component of alternating diagonals in an inner region of the core, and the highest burned or equivalent assemblies occupy the other checkerboard component. The remainder of the core consists of an outer region containing another checkerboard of feed assemblies wherein the feed assemblies occupy less than one-half the assembly locations on the core periphery.

Abstract: A core construction of a nuclear reactor wherein the fuel charge in the core has 1/4 symmetry and fuel assemblies adjacent a control rod (10) constitute a core unit. In the central portion of the core, each core unit (12) is composed of one thrice burned fuel assembly (3), and three once (1) or twice (2) burned fuel assemblies. One of the two types of fuel assemblies which includes two fuel assemblies located on a diagonal line in the respective core unit. In the core as a whole, the fuel assemblies of the same type or the same burning cyclic period are located on a diagonal line (E,F,G).

Abstract: A core construction of a boiling-water nuclear reactor including an array of fuel assemblies and control rods wherein the fuel assemblies are each divided into two sections or upper and lower sections in the vicinity of the center of the length thereof and each lower section has a smaller mean infinite multiplication factor than each upper section. Of the fuel assemblies, those fuel assemblies which are located adjacent the control rods selected for power control each have a smaller overall means infinite multiplication factor than those fuel assemblies which are located adjacent the control rods other than the selected control rods.

Abstract: An arrangement of square fuel assemblies in the first and subsequent cycles of a pressurized water nuclear reactor wherein shimmed feed assemblies and once-burned or equivalent assemblies occupy the same checkerboard component of alternating diagonals in an inner region of the core, and the highest burned or equivalent assemblies occupy the other checkerboard component. The remainder of the core consists of an outer region containing another checkerboard of feed assemblies wherein the feed assemblies occupy less than one-half the assembly locations on the core periphery.

Abstract: The production of a novel nuclear fuel, utilizing uranium 233 low in uranium 232 content in combination with other nuclear materials is made possible by utilization of an equally novel reactor configuration and method of operation. Uranium 233 is produced from thorium in a light water reactor (LWR) while utilizing discrete separation of the thorium being irradiated from the fissile fuel. This uranium 233 is then incorporated directly as fissile isotope enrichment into a new nuclear fuel which may be done without encountering the usual difficulties and hazards in the handling of uranium 233 or the expense and delays associated with gaseous diffusion enrichment. Thorium from this process may be directly reprocessed for reactor charging without radiation hazard also.

Abstract: The production of a novel nuclear fuel, utilizing uranium 233 low in uranium 232 content in combination with other nuclear materials is made possible by utilization of an equally novel reactor configuration and method of operation. Uranium 233 is produced from thorium in a light water reactor (LWR) while utilizing discrete separation of the thorium being irradiated from the fissile fuel. This uranium 233 is then incorporated directly as fissile isotope enrichment into a new nuclear fuel which may be done without encountering the usual difficulties and hazards in the handling of uranium 233 or the expense and delays associated with gaseous diffusion enrichment. Thorium from this process may be directly reprocessed for reactor charging without radiation hazard also.

Abstract: Disclosed is a process for reloading the contaminated empty reactor cavity of a nuclear reactor with spherical operating elements forming the core of a high temperature reactor comprising supplying the operating elements to the reactor cavity first through a central loading tube in the roof reflector of the nuclear reactor to a predetermined load level, the loading tube being extended at the onset of the loading process toward the floor reflector and being adjusted upwardly during continued loading with the rising load level and after reaching the predetermined load level, supplying further operating elements through a plurality of auxiliary loading tubes in the roof reflector of the nuclear reactor in concentric circles about the central loading tube with the loading sequence proceeding circle after circle beginning with the circle closest to the central loading tube.

Abstract: A method and arrangement for utilizing mixed oxide fuel in the core of a nuclear reactor controlled by rectilinearly movable control rod elements which decreases the maximum single control rod element worth in the core. Fuel elements containing the mixed oxide fuel are positioned at discrete core locations, particularly at those locations receiving high worth control rod elements, thereby decreasing the worth of those control elements.

Abstract: There is provided a novel initial core arrangement of a nuclear reactor. The fuel assemblies in the central region of the reactor core occupying more than 50% of the total area of the reactor core are grouped into a plurality of fuel units each of which being constituted by four adjacent fuel assemblies. The fuel assemblies in each fuel unit are replaced one by one at each fuel replacement cycle with a new fuel assembly. The initial core is so arranged that each fuel unit has one gadolinia containing high enrichment fuel assembly and three low enrichment fuel assemblies containing no gadolinea. This arrangement permits a stable reactor operation substantially equivalent to that obtained in the state of equilibrium (equilibrium core), even with an initial core.

Abstract: A method of refueling a nuclear reactor having a core containing a plurality of fuel rod bundles which are built up from a plurality of fuel rods includes replacing at least one burnt up fuel rod bundle with a fuel rod bundle which is at least partly composed of fuel rods from other fuel rod bundles burnt up in the reactor, the mean content of fissile material in the fuel rod bundle thus composed being higher than the mean content of fissile material in the fuel rod bundle which is replaced by the composed fuel rod bundle.