Abstract: A fuel assembly is disclosed which comprises a fuel channel (1) with square cross-section supported by an inlet sleeve (22) having at its lower part an inlet opening for a flow of coolant flowing through the fuel assembly. The inlet sleeve (22) is made of stainless steel and is mechanically connected to a transition sleeve (21) made of thick zirconium alloy sheet, which is welded to the more thin-walled fuel channel (1).

Abstract: A nuclear fuel assembly includes and upper yoke, a base, an elongated, outer flow channel disposed substantially along the entire length of the fuel assembly and an elongated, internal, central water cross, formed by four, elongated metal angles, that divides the nuclear fuel assembly into four, separate, elongated fuel sections and that provides a centrally disposed path for the flow of subcooled neutron moderator along the length of the fuel assembly. A separate fuel bundle is located in each of the four fuel sections and includes an upper tie plate, a lower tie plate and a plurality of elongated fuel rods disposed therebetween. Preferably, each upper tie plate is formed from a plurality of interconnected thin metal bars and includes an elongated, axially extending pin that is received by the upper yoke of the fuel assembly for restraining lateral motion of the fuel bundle while permitting axial movement of the fuel bundle with respect to the outer flow channel.

Abstract: A spacer for use in a fuel assembly of a nuclear reactor having thin, full-height divider members, slender spring members and laterally oriented rigid stops and wherein the total amount of spacer material, the amount of high neutron cross section material, the projected area of the spacer structure and changes in cross section area of the spacer structure are minimized whereby neutron absorption by the spacer and coolant flow resistance through the spacer are minimized.

Abstract: A fuel assembly for a boiling water reactor is provided with at least one vertical water channel (4, 5) for a by-pass flow through the fuel assembly. At its lower end the channel is connected to a radial tube (10) which opens out at the outer side surface of the fuel assembly. Below the radial tube, the wall of the assembly base (2) is provided with a through-hole (12).

Abstract: A fuel assembly for a boiling water reactor comprises a plurality of fuel rods (2, 2'), which constitute four partial bundles and are surrounded by a fuel channel system (1) comprising one partial tube for each partial bundle. Each of the four partial bundles rests on a bottom tie plate (19) and is positioned with respect to the others by means of a common top tie plate (31), which is provided with a lifting loop (33) which is sufficiently strong to be able to lift the four partial bundles simultaneously, a major part of the lifting force being transmitted to said bottom tie plates via a plurality of supporting fuel rods (2').

Abstract: Fuel assembly having square cross-section and a plurality of tube elements (7,8) arranged in a square reactor lattice, at least one of said tube elements being water tubes (8) and a predominant number being fuel rods (7). Each fuel channel wall has a hollow projection (9) lying in a vertical mid-plane. The number of tube elements between two projections (9) lying in the same mid-plane is smaller than nine and greater than two. A plurality of rows of nine tube elements (7, 8) are arranged in parallel with each of the mid-planes.

Abstract: In a fuel assembly for a nuclear reactor a fuel element spacer formed of an array of laterally positioned cojoined tubular ferrules each providing a passage for one of the fuel elements, the elements being laterally supported in the ferrules between slender spring members and laterally oriented rigid stops.

Abstract: A blanket assembly for a nuclear reactor core perimeter region having at least two regions within the assembly of different H/U ratios and rod enrichments.

Abstract: A boiling water reactor fuel assembly is provided with an elongated, vertical stiffening device having four stiffening wings which are each attached to a wall of the fuel box. Each stiffening wing has at least one vertically directed passageway for water.

Abstract: Nuclear fuel assemblies having square cross-sections mount tubes at each corner, the tubes containing springs which are extended through apertures in the tube walls when actuated by solid rods extended down into the tubes by the weight of the upper guide structure of the nuclear vessel in which the fuel assemblies are mounted. The springs, extended from strategically located positions along the length of the tubes, engage the surface of adjacent fuel assemblies to dimensionally stabilize the fuel assemblies relative to each other and the vessel in which they are mounted.

Abstract: In a cluster of nuclear fuel rods cooled by liquid metal an obstruction to coolant flow results in overheating in the wake of the obstruction. By the provision of open ended heat transfer tubes in the flow channels, a guaranteed supply of coolant is maintained and this supply holds the temperature to below saturation. Heat transfer via the tubes is highly efficient and ensures that a sufficient temperature rise occurs at the cluster exit to provoke a response from the outlet temperature transducer sensing average temperature.

Abstract: A fuel assembly for a nuclear reactor including a plurality of fuel rods held in spaced, parallel position between upper and lower tie plates and retained in lateral position by intermediate spacers and having a water tube in lieu of a fuel element in one or more of the rod positions, the water tubes having an outside diameter greater than that of the fuel rods and the spacer springs in the spacer cells of the water tubes being modified to accommodate the larger diameter of the water tubes.

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.