Patent Number: 047056630
Section: summary

The invention relates to a nuclear reactor fuel element with mutually parallel rods, particularly fuel rods containing nuclear fuel, and a rectangular, grid-shaped spacer with grid mesh openings respectively receiving rods, including outer webs crossing and flatly facing the rods at right angles to the rods, the spacer having an outward curve formed from two outer webs on an outer corner of a corner grid mesh opening located between the two outer webs, being curved in a direction parallel to the longitudinal direction of the rods. A nuclear reactor fuel elelemnt of this type is known from French Patent of Addition No. 91 358 corresponding to U.S. application Ser. No. 482,792 and British Pat. No. 1,153,743. This conventional nuclear reactor fuel element is particularly intended for a boiling water nuclear reactor. The device includes a so-called duct tube formed of sheet metal which is pushed over the nuclear reactor fuel element with spacers and which rests with two sheet metal cross strips on the inside of the corners of the upper end of the fuel element, on two stay bolts on the top of a grid plate belonging to the fuel element head. The sheet metal cross strips are respectively screwed to the stay bolts with a screw penetrating the corss strips. The spacers of this nuclear reactor fuel element have outer webs with a width that is reduced at the curves on the outer corners of the grid mesh openings. When the duct tube is pushed onto the nuclear reactor fuel element, there is a danger that the duct tube will rotate with respect to the nuclear reactor fuel element about the longitudinal axis of the duct tube, as seen in cross section, so that the lower edge of the duct tube rests directly on an outer corner of a corner grid mesh opening of a spacer and becomes caught there. This danger arises particularly when a used duct tube, and therefore one which is somewhat twisted, for example, around its longitudinal axis, is pushed onto the nuclear reactor fuel element. No duct tubes are associated with nuclear reactor fuel elements which are intended for a pressurized water nuclear reactor, but in the reactor core of such a pressurized water nuclear reactor there are a series of similarly constructed nuclear reactor fuel elements with parallel longitudinal axes, disposed like chess board squares closely adjacent each other. Therefore, when loading or unloading a pressurized water nuclear reactor with the individual nuclear reactor fuel elements, nuclear reactor fuel elements, especially those diagonally adjacent each other in the reactor core, can still become caught at the outer corners of the corner grid mesh openings of their spacers when the spacers are constructed as in the conventional nuclear reactor fuel elements intended for boiling water nuclear reactors. This type of hooking of diagonally adjacent nuclear reactor fuel elements can lead to a destruction of the outer webs of the spacers of these nuclear reactor fuel elements, so that these nuclear reactor fuel elements cannot be re-inserted into the reactor core of the pressurized water nuclear reactor. Nuclear reactor fuel elements which have become greatly warped in the reactor core due to operational stresses have a particular tendency to become caught. It is accordingly an object of the invention to provide a nuclear reactor fuel element which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, to avoid using spacers when duct tubes are pushed onto nuclear reactor fuel elements and to avoid the hooking of spacers to spacers of adjacent nuclear reactor fuel elements when nuclear reactor fuel elements are inserted into reactor cores. With the foregoing and other objects in view there is provided, in accordance with the invention, a nuclear reactor fuel element for receiving mutually parallel rods especially fuel rods containing nuclear fuel, comprising a rectangular grid-shaped or latticed spacer including planar webs crossing and facing the rods at right angles defining grid mesh openings receiving the rods, the webs including two outer webs forming an outer corner of the spacer and defining a corner grid mesh opening at the outer corner, the outer corner having an outward curve being curved around a direction parallel to the longitudinal direction of the rods, the outer webs having edges at the curve transverse to the rods being drawn inward toward the rods in the corner grid mesh opening forming a bevel in longitudinal direction of the rod. The edges of the two outer webs drawn in toward the rod ensure a hooking-free sliding of both a duct tube and a spacer of an adjacent nuclear reactor fuel element in a reactor core. In accordance with another feature of the invention, the edges of the outer webs form edges of a channel on the curve. This channel can ensure coolant flow on the outside of the rod passing through the corner grid mesh opening of the spacer, which is not obstructed by the spacer. In accordance with a concomitant feature of the invention, the two outer webs together include a one-piece angular part forming the curve and a remaining part of each outer web secured to the angular part at locations spaced from the curve. Thus it is possible to avoid fastening points of the two outer webs with overlapping on the curve which encourages hooking. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a nuclear reactor fuel element, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.