The method applied today to produce tableting fuel for fuel cells includes preparation of press-powder of uranium dioxide UO₂, enriched with uranium-235 up to 2-5%, mixing with a dry bounder (zinc stearate Zn(C₁₇H₃₅COO)2 and U₃O₈ uranium oxide powder), pressing with a lubricator in a matrix, thermal removal of the bounder, caking of tablets in a gaseous reducing medium, wet polishing of the tablets with an diamond disk, drying and separation of defective tablets. In accordance with a newly-proposed technology, UO₂ powder obtained in the process of wet transformation with consequent reduction from ammonia diuranate is used. Sealing operation is eliminated. UO₂ is mixed with a dry bounder, zinc stearate, in several stages. At the first stage, 5-10 parts of the UO₂ powder with a full amount of the zinс stearate required for the batch. At the second stage, the obtained mixture is mixed with 5-10 parts of the UO₂ powder of the batch. At the third stage, the obtained mixture is mixed with the rest amount of the UO₂ powder, and with U₃O₈, received after thermal oxidation of the UO2 defective tablets with an air. Zinc stearate, previously introduced in the press-powder, is used as a lubricant. To perform a wet polishing of the tablets surface after their caking in a reducing medium, a set of disks is used. Diamond layer of the disk is chosen for an operation to be executed, i.e. for coarse or fine polishing. The width of the surface of all the disks is determined under the following equation:

L = L₁ + H,

where L - disk diamond surface width; L₁ - driving disk width; H - tablet height.

In the tablet polishing installation, lower and upper supports are fixed in accordance with the following formula:

X = D + A + 0.1 mm,

where X - a height from the upper support lower edge to lower support upper edge; D - tablet diameter, mm; A - maximal cutting-off margin per one polishing run and

X₁ = N - M + a - M₁,

where X₁ - lower support height; N - a distance from a support base plane to the disk center line, mm; M - a distance from a support base plane to the supporting surface of the support, mm; M₁ - a distance from a tablet center line to the disk center line, mm; a - a value equal to the difference between the 0.5 tablet diameter and a distance from the line, a tablet moves over the supporting surface of the lower support, to the lower support edge.

Then, a drying process is effected in the inert gas medium.

Five modification of the main method are described in the patent. In the first modification of the method, zinc stearite amount required per batch is 0.2-0.5%. In the second modification of the method, the amount of the regenerated U₃O₈, to be introduced in the press-powder batch, is up to 15%. In the third modification of the method, a process of thermal removal of a bounder from tablets is carried out at the temperature of 400-700° C. In the fourth modification of the method, drying of tablets after wet polishing is effected in a nitrogen medium at temperatures of 200-300° C. In the fifth modification of the method, an air with a temperature of 500-600° C is used to oxidize defective tablets.

The installation used nowadays to produce tableting fuel for fuel cells includes: a device to mix UO₂ powder with a zinc stearite; an aggregate to press tablets from the UO₂ powder/zinc stearite mixture equipped with a matrix; a device to cake tablets, which includes a tunnel furnace with three temperature zones for heating and caking tablets in a reducing medium (to be cooled, moving “boats” with tablets pass through the three temperature zones of the furnace); a machine for wet polishing of tablets surface and aggregate for tablets drying. The newly-developed device is equipped with an aggregate for treating defective tablets which comprises a vertical furnace, a unit for loading defective tablets, a unit for unloading U₃O₈ powder, and an inlet sleeve to inject gaseous reducing medium in the furnace. An aggregate for caking the tablets is equipped with a movable box to collect “boats” with tablets inside it. It’s also equipped with movable loading box manufactured with joint to connect with the movable box-collector.

Afanasiev V.L.

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