Abstract: In a method of fabricating a channel box for use in a nuclear reactor, Zr-alloy sheet material is formed into a tubular channel box. The method includes solution heat treatment of the Zr-alloy sheet material including quenching from a temperature at which .beta.-phase is present. After the solution heat treatment, portions of the Zr-alloy sheet are thinned relative to other portions by a non-stressing thinning process, such as chemical etching in a bath. The corrosion resistance imparted by heat treatment is retained, and the heat treatment itself is easily performed on material of uniform thickness.

Abstract: A fuel assembly, where crystallographic orientations of a channel box are brought into a random distribution; and cladding tubes, spacers and a channel box are made from highly corrosion-resistant, Fe--Ni, zirconium-based alloy, hardened in the (.alpha.+.beta.) phase or .beta.-phase temperature region, has an average discharge burnup level of 50 to 550 GWd/t.

Abstract: A fuel assembly comprises a plurality of fuel rods supported by an upper tie plate and a lower tie plate respectively at each of upper end portion ad lower end portion, and a channel box surrounding a bundle of the fuel rods and the lower tie plate. The fuel assembly forms a natural uranium region at lower end portion of effective fuel length portion. A wall thickness at a lower thick wall region of the channel box is thicker than the wall thickness at a region disposed upwardly from the lower thick wall region and between corner portions of the channel box. An upper end of the lower thick wall region is disposed from an upper side of the lower tie plate and downwardly from an upper end of the natural uranium region. A wall thickness at the corner portion of the channel box is thicker than the wall thickness at a middle portion of the side wall between the corner positions at the region locating upward from the lower thick wall region.

Abstract: A nuclear fuel assembly for a nuclear reactor has a plurality of vertically extending fuel rods arranged side by side in a square array and containing fissile material. The array has two adjacent first sides which are next to a control rod region of the core and two adjacent second sides which are next to a non-control rod region of the core.

Abstract: A control rod assembly for a boiling water reactor comprises a tie-rod of a cross-shaped section, and four sheaths. Each of the sheaths is of a U-shaped section and mounted to the respective arms of the tie-rod. One or more neutron absorber materials are disposed within a space defined by the arm and the sheath. The neutron absorber material is axially separated into two portions. One of two portions is supported by a supporting member. The other portion is suspended by a handle.

Abstract: A nuclear fuel assembly has a plurality of fuel rods and a lower tie plate supporting their lower ends. Coolant apertures extending through the lower tie plate. A channel box surrounds the fuel rods and receives the lower tie plate, to confine the coolant. To restrict leakage of coolant between the tie plate and the channel box, the coolant apertures include, adjacent the periphery of the lower tie plate, a plurality of peripheral apertures which are located at least partly outside the outermost fuel rods. The peripheral apertures each provide a coolant velocity peak located further from the axial center line of the tie plate than the axial center lines of the closest neighboring fuel rods. The invention also provides venturis in the leakage path between the channel box and the tie plate, to restrict deformation of the tie plate.

Abstract: A fuel assembly including a plurality of fuel rods and water rods. The fuel rods are arranged with a predetermined pitch and two water rods are disposed adjacent to each other in a diagonal direction of the fuel assembly. More particularly, the fuel rods are arranged in a lattice of nine rows by nine columns and the two water rods are disposed inside a region corresponding to a space sufficient for disposing seven fuel rods at the center of the fuel assembly. Each of the water rods has an outer diameter greater than the pitch of the fuel rods.

Abstract: A fuel assembly according to the present invention is formed in such a manner that the small diameter portion of an upper end plug of a fuel rod is inserted into a boss of an upper tie-plate. The upper end plug includes a small diameter portion and a large diameter portion which is disposed below the former. An expansion spring in disposed in the small diameter portion of the upper end plug. A cover member surrounding this expansion spring is disposed in the large diameter portion of the upper end plug, and extends upwardly. Since the cover member surrounds the expansion spring, pressure loss caused by the expansion spring can be reduced.

Abstract: A fuel assembly has a fuel spacer consisting of a water rod having an outer diameter greater than that of fuel rods and a large number of circular sleeves into which the fuel rods are inserted. The fuel spacer has four bridge members. Both ends of these bridge members are fitted to two of eight circular sleeves which are adjacent one another in the diagonal direction of the fuel spacer. Both ends of each bridge member are bent so that its center projects outwardly away from the water rod.

Abstract: An apparatus for detecting failure of the nuclear fuel rod has an outer cap and 16 (sixteen) inner caps. In checking for any faulty fuel rods, the outer cap is placed to cover the upper ends of 16 (sixteen) fuel assemblies mounted in the reactor core, while the inner caps in the outer cap are disposed on corresponding one of the fuel assemblies. To the outer cap are attached 4 (four) air supplying hoses. The inner caps receive corresponding one of 16 sampling tubes attached to the outer cap, and coolant sampling hoses are connected to the sampling tubes. A bundle member is fixed to the center of the upper surface of the outer cap. The four air supplying hoses and 16 coolant sampling hoses are fixed to the bundle member. The bundle member has a handle attached thereto.