Patent Number: 039883973
Section: description

Referring more specifically to the drawings in which like numbers refer to like parts: In FIG. 1 uranium containing feed zones 6 of small diameter are located in a hexagonal arrangement in a graphite matrix 30 around a central thorium containing breed zone 4. Cooling channels 2 are disposed in hexagonal arrangement around the uranium containing zones. FIG. 2 shows a narrow graphite zone 32 around a central thorium containing breed zone 10 and an uranium containing feed zone enclosing said graphite zone, around which feed zone the outside cooling channels 8 are disposed hexagonally in the graphite matrix 34. FIG. 3 shows a hexagonal arrangement of uranium containing feed zones 18 around a central cooling channel 14, around which feed zones there are hexagonally disposed thorium containing breed zones 16 in the graphite matrix 36. In the case of all three embodiments, enough graphite structural matrial is disposed between the individual zones, so that these zones can be drilled separately from one another. Thus these zones are directly connected with the surrounding fuel free graphite matrix. In order to explain the invention more clearly, the following example is described. From a graphite mixture molding powder consisting of natural graphite, graphitized petroleum coke and a binder resin, a pressable and isotropic graphite granulate was produced by cold precompaction and subsequent comminution. In the specific example there was used a mixture of 60 weight % natural graphite, 20 weight % graphitized petroleum coke and 20% of a phenol formaldehyde resin having a softening point of about 100 .degree. C. and molecular weight 700. This composition is described in more detail in example 1 of the aforementioned Hrovat application Ser. No. 218,244. The molding powder for preparation of the granulate can be made from a mixture of natural graphite and binder resin, synthetic graphite and binder resin or a mixture of both types of graphite with binder resin. When both types of graphite are employed they can be used in any proportions, e.g. 1 to 99% of either by weight. In place of the phenol-formaldehyde resin employed in the specific example there can be used phenol formaldehyde resins with other softening temperatures, e.g. 60.degree. to 120.degree. C. as well as xylenol-formaldehyde, cresol-formaldehyde and furfuryl alcohol resins. The binder resin is normally used in an amount of 10 to 30% of the total of resin and graphite by weight. From the granulate, a prismatic block 40 with pressed in channels as shown in FIG. 4 was prepressed hot at a temperature of less than 100.degree. C. at 50 kg/cm.sup.2. Prefabricated cylinders consisting of graphite matrix and coated fuel particles were inserted in the channels provided for reception of the feed particles 24 or the breed particles 22. Subsequently, metal bars necessary for the maintenance of the cooling channels were inserted. As can be seen from FIGS. 1 and 4 the recurring arrangements of feed zones, breed zones and cooling channels are in repetitive sequence. After that, the element was final pressed at 90 kg/cm.sup.2 to its final dimensions at an elevated temperature, specifically 150.degree. C. After removal of the metal bars, the element was subjected to a final heat treatment at 1800.degree. C. This final treatment can be at a temperature range of 1500.degree. to 2100.degree. C. The pressures and temperatures employed in preparing the fuel elements of the present invention are not critical and can be any of those conventionally employed in the art. The coated fuel particles employed were uranium 235 oxide nuclei coated with pyrolytic carbon. The breed particles were thorium oxide. There can be used other fuel particles with other breeder (or fertile) materials such as those mentioned in Hrovat application Ser. No. 218,244.