Patent Number: 040100693
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the fuel rod consists of a tubular casing 1, a nuclear fuel charge 2, which may be in the form of pellets, a lower end cap 3, an upper end cap 4 having a central hole 4a as well as a spring 5 for holding down the nuclear fuel pellets 2, and activated carbon filter material 6. This filter material 6 may be pressed into the fuel rod and enclosed by a tubular casing 7 having the same outside diameter as the tubular casing 1. This tubular casing 7 on one end is welded to the upper end cap 4 and on the other end is "plugged" by means of an intermediate cap 8, thus forming a container of its own. It also is welded to the rest of the fuel rod, i.e., to the tubular casing of the latter, 1. The intermediate cap 8 has a central hole 8a to pass the fission products, and a cup-shaped recess to receive a porous element 9, which is particularly used to feed the fission products to the filter zone 6 in a finely distributed state without a large pressure drop. A material through which the fission products can diffuse, such as for example, porously sintered Al.sub.2 O.sub.3, is therefore particularly advantageous for this purpose. The retention time of the fission products in the filter material is also influenced by a similar porous or diffusable material 9 in front of the hole 4a of the end cap 4. In the embodiment shown in FIG. 2, only the upper portion of the fuel rod is shown. Similar parts are again labelled with the same reference symbols. Here, the tubular casing 2 passes through from the lower end cap 3 to the upper end cap 4; the filter material consisting of activated carbon 6 is located in a separate container inside this tubular casing 2. The container formed on the one hand by tubular part 7, a filter end cap 8b having a hole 8a and an end cap 4, to which the cylindrical part 7 is welded. As shown in FIG. 1 the porous material 9 is located at both ends of the activated charcoal or other type of filter material 6. The embodiment shown in FIG. 2 has the great advantage that the tubular casing is undivided and passes through the entire length of the fuel rod without additional welded joints. FIG. 3 illustrates a minor modification which can be made in this container, containing the filter material. Here, a separate filter end cap 8b is dispensed with and instead, the porous material 9 is inserted into the tube 7 as an end plug 9a and is joined to the porous material in a gastight manner, for example, by a hard-solder joint 10. The element 9 of porous material also can be connected with the end cap material in a gastight manner on the other side of the filter insert. In this way, additional bypass possibilities, which have a reducing effect on the retention time of the fission products, are avoided. By means of these design possibilities or the underlying principle, it is possible not only to improve very considerably the operation of the fission gas venting system, but it is also possible to manufacture the container which encloses the filter material 6 by separate operations, so that in the manufacture of the fuel rods the filter material can be inserted without additional handling problems. It is further more an essential feature of the invention that the filter material is pressed into the container. It is advantageous here in particular if the diameter of the container, after being filled, is reduced by commonly known methods and the contact with the filter material is improved, which is not possible in known fuel rod designs with filter zones. In the foregoing, the invention has been described in reference to specific exemplary embodiments. It will be evident however, that variations and modifications, as well as the substitution of equivalent constructions and arrangements for those shown for illustration, may be made without departing from the broader scope and spirit of the invention as set forth in the appended claims. The specification and drawing are accordingly to be regarded in an illustrative rather than a restrictive sense.