Fuel element for a pressurized water reactor

#The invention relates to a fuel element for a pressurized water reactor, with a laterally open skeleton containing control-rod guide tubes, to which are fastened a plurality of spacers and also a fuel element head and a fuel element foot. Gastight multilayer cladding tubes are inserted into the skeleton and in each case surround a column of fuel pellets.

#FIG. 1 illustrates a fuel element of this type, with a head 1, a foot 2 and spacers 3 and 4 that are fastened to guide tubes 5, thus producing a laterally open skeleton, into which fuel rods 6 are inserted. During operation, cooling water flows from the bottom upward through the fuel element and can also enter adjacent fuel elements laterally from the interspaces between the fuel rods. It can also be seen from FIG. 1 that additional mixing grids 7, which serve as carriers for flow guide blades, may be provided between the spacers 4 in an upper part of the fuel element. Such flow guide blades are advantageously likewise provided in the upper part of the fuel element, at least on a top side of the spacers 4, in order to achieve a turbulent mixing of the cooling water and a better flow onto the fuel rods 6.

#Corresponding blades are described, for example, in Published, Non-Prosecuted German Patent Application DE 15 64 697 A and are reproduced in FIG. 2. It is also possible, however, to have other spacers (for example, formed of sleeves welded to one another) and other geometries of flow guide blades 8, while a different number of mixing vanes may also be provided in the interspaces between adjacent fuel rods 6.

#FIG. 1 is a diagrammatic, side-elevation view of a pressurized water fuel element according to the invention;

#FIG. 2 is a fragmentary, perspective view of guide blades that are advantageous at least on some spacers or intermediate grids;

#FIG. 3 is a graph showing a corrosion rate on the parameter A of the standardized annealing duration on a surface of a pressurized water fuel rod;

#Referring now to the figures of the drawing in detail and first, particularly, to FIG. 6 thereof, there is shown a cladding tube 10 of the fuel rods 6 is in each case closed in a gastight manner at upper and lower ends by an end plug 11. At the upper end a spring 12 subjected to compressive stress ensures that a corresponding plenum 13 is maintained at least at the upper end. A column of fuel pellets 14 contains in each case, at its upper and lower end, a body 15 that contains virtually no fissionable material and may consist, for example, of aluminum oxide or else natural uranium or depleted uranium. In this case, in order to increase conductivity between the pellets 14 and the cladding tube 10, the cladding tube 10 is filled with a high-pressure gas (for example, helium).

#In the present case, a supporting body 16 at the lower end of the fuel rod also keeps free a corresponding plenum.

#The outside diameter of the cladding tube is about 9.55 mm, and its wall thickness is about 0.61 mm. According to FIG. 7, a cladding tube 20 is formed of a matrix 21, the thickness of which is about 75 to 95% of a cladding tube wall. A protective layer 22 is bound metallurgically to the matrix 21 on the inside of the cladding tube 20, and it is also indicated that a further protective layer 22′ may also be attached to the outside.