Abstract: A fuel assembly includes an array of fuel rods and guide thimbles disposed in laterally spaced relation to one another. The guide thimbles have upper ends extending above the upper ends of the fuel rods. The fuel assembly also includes a top nozzle defined solely by a flat rectangular adapter plate having a main central portion and a peripheral portion surrounding and merging with the main central portion. The main central portion of the adapter plate has a plurality of attachment holes receiving the upper ends of guide thimbles for attachment of the adapter plate upon the guide thimble upper ends in spaced relation above the fuel rod upper ends. A first sest of holes are defined through one pair of diagonal corners of the adapter plate for use in attaching sets of spring assemblies directly to and upon the adapter plate for alignment along the peripheral portions thereof.

Abstract: In a nuclear reactor, the core is composed of fuel assemblies disposed in side-by-side spaced relationships with an outer group thereof defining the periphery of the core and an inner group thereof positioned inwardly of the outer group. A baffle structure extends about the reactor core adjacent the fuel assemblies in the outer group. Any jetting of coolant fluid through the baffle structure will impinge upon fuel rods in the outer group of fuel assemblies so as to cause vibration of the fuel rods. To prevent such vibration, a plurality of annular anti-vibration grids are axially spaced along and connected to guide thimbles of the fuel assemblies in the outer group thereof between at least some of the support grids of such fuel assemblies. The annular grids are separate from and unconnected to the support grids.

Abstract: The mechanical spectral shift reactor provides a method and apparatus for controlling a nuclear reactor comprising inserting a plurality of reactor coolant displacer members into the reactor at the beginning of the core life. The displacer members reduce the volume of reactor coolant-moderator in the core at the start-up. As the reactivity of the core declines with fuel depletion, a selected number of displacer members are withdrawn from the core at selected time intervals. The withdrawal of the displacer member allows reactor coolant water to enter the core which increases core moderation at a time when fuel reactivity is declining. Thus for a given amount of nuclear fuel the life of the core can be extended or for a given life of a core the uranium fuel requirements can be reduced.

Abstract: In a nuclear fuel assembly having a plurality of separate fuel bundles secured therein in separate compartments, coolant flow paths are provided to enable the flow of coolant between the separate compartments, thereby equalizing the hydraulic pressure between the separate compartments and minimizing the possibility of thermal-hydrodynamic instability between the separate fuel bundles in the nuclear fuel assembly. A plurality of coolant flow paths are formed through solid structural ribs secured to an outer flow channel of the nuclear fuel assembly to permit coolant flow between the separate compartments.

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 segmented fuel and moderator rod and fuel assembly for a BWR. The segmented rod has a lower fuel region and an upper moderator region for passing coolant having a void fraction of between about 0-20% through the upper portion of the BWR core which is normally undermoderated. The segmented rod displaces one or more conventional fuel rods in the fuel bundle. A method of moderating a BWR core is also disclosed.

Abstract: A control rod assembly arrangement is disclosed for a light water nuclear reactor. Absorber rods are combined with stainless steel rods to achieve a more homogeneous poison distribution effect which reduces power depression within associated fuel assemblies and thereby flattens the overall power distribution within the core. In addition to improved load follow performance, safety analysis margins are improved due to the reduction in control rod reactivity worth.

Abstract: A soluble burnable absorber 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 neutron absorber material in liquid form, preferably boric acid with an enhanced concentration of boron isotope B-10, is contained within the chamber. The tubular body has reinforcing convolutions formed therein for strengthening the body to withstand external pressure acting thereon. Also, one of the end plugs acts as a hydride sink and a hydrogen getter material is disposed adjacent the other end plug.

Abstract: A boiling water nuclear power reactor includes an improved control rod associated with each of its clusters of fuel assemblies. The control rod has an elongated central stem defining a longitudinally extending internal central gas plenum and a plurality of blades orthogonally arranged in pairs to provide a cruciform configuration in which the blades connect to and extend radially outward from the central stem. Each blade incorporates a series of internal cavities arranged in columns and rows across the length and width of the blade, and a neutron absorbing pellet is disposed in each cavity. The cavities communicate with the central plenum so that any gases generated by irradiation of the pellets can expand into the plenum. The cavities and pellets are arranged to form a longer, constant worth section in a body portion of each blade and a shorter, reduced worth section in an end tip portion of each blade.

Abstract: A control rod with a "reduced worth" tip is provided for a nuclear reactor which includes an elongated tubular cladding with its opposite ends closed and having a plurality of pellets of two different types disposed in its lower end portion in an end-to-end relationship. One type of pellets is formed of a neutron absorbing material, such as B.sub.4 C, whereas, the other type of pellets is formed of an inert material, such as ZrO.sub.2. The absorber pellets and the inert pellets are interspaced between one another in the lower end of the rod so as to gradually reduce the rate of change of the neutron flux experienced at the rod's lower end portion as it moves in and out of the fuel assembly to thereby alleviate pellet-clad-interaction and thus reduce the likelihood of fuel rod failure. In one embodiment, the axial heights of the absorber pellets progressively increase from the bottom to the top of the rod's lower end portion while the axial heights of the interspaced inert pellets remain constant.