Patent Number: 049851837
Section: description

EXAMPLES The following examples are cited to prove the usefulness of the invention. EXAMPLE 1 ADU (ammonium diuranate), produced by the reaction between 300 gU/l of UO.sub.2 F.sub.2 aqueous solution and aqueous ammonia, was calcined and reduced to form UO.sub.2 powder. After 0 to 1.5% by weight of pore-former agents, whose particle size had been adjusted to several different particle sizes, was uniformly added to the UO.sub.2 powder, the pressed bodies were formed under the pressure of 3 t/cm.sup.2 by the use of various compacting processes as described above. Ammonium oxalate and zinc stearate were selected as the pore-former agent and the lubricant, respectively. The pressed body was heated to 1750.degree. C. for four hours in hydrogen atmosphere to produce sintered pellets. Table 1 shows the relationship between pellets fabrication conditions and physical properties of the pellets. As is clearly seen from Table 1, the pellets fabricated by the processes according to the present invention have a sintered density between 94 and 97% TD. Furthermore, significant reduction of the crystalline grain size, and reduced probability of having large pores, both due to the presence of a pore-former agent, is apparent. TABLE 1 __________________________________________________________________________ Pore-Former Agent Fabrication Process Physical Properties of Pellets Particle Granula- Grain Size Addition tion Open Density Size No. (.mu.m) (wt. %) (.mu.m) Lubricant Porosity (% TD) (.mu.m) Overall Evaluation __________________________________________________________________________ A-1 5-10 1.0 None Mold Small 95.3 45.4 Excellent Coated A-2 10-100 " " Mold " 95.6 50.6 " Coated A-3 100-1000 " " Mold " 95.4 49.8 " Coated A-4 10-100 0.3 " Mold " 97.4 51.3 " Coated A-5 " 0.8 " Mold " 95.9 50.5 " Coated A-6 " 1.4 " Mold " 94.0 50.9 " Coated A-7 " 1.0 " None " 95.5 49.6 " A-8 " " " Mixing " 94.9 45.2 " Powders A-9 " " less than None " 95.3 50.1 " 2000 A-10 " " less than Mold " 95.4 51.8 " 2000 Coated A-11 " " less than Mixing " 94.8 46.4 " 2000 Powders B-1 -- 0 None Mold Small 99.3 50.3 High density Coated B-2 less 1.0 " Mold " 95.4 37.9 Significant Reduction than 5 Coated of Grain Size B-3 500-1000 " " Mold Large 95.0 51.2 Large open porosity Coated B-4 10-100 0.2 " Mold Small 98.0 48.9 High density Coated B-5 " 1.5 " Mold " 93.4 49.2 Lower density Coated __________________________________________________________________________ EXAMPLE 2 One or more compounds were selected as pore-former agents from the group consisting of ammonium acetate (C 1), ammonium carbonate (C 2), ammonium bicarbonate (C 3), ammonium oxalate (C 4), ammonium alginate (C 5) and stearic acid (C 6). 1.0% by weight of the selected compound or mixture thereof was added to the same UO.sub.2 powder as in Example 1. The resulting UO.sub.2 powder was subjected to rough compacting, pulverization and granulation to form granules. Subsequently, one or more compounds were selected as a lubricant from the group consisting of stearic acid (D 1), zinc stearate (D 2), lithium stearate (D 3), stearic amide (D 4), ethylene-bis-stearic amide (D 5), methylene-bis-stearic amide (D 6) and polyethylene glycol (D 7), and 0.2% by weight of the selected compound or compounds was added to the granules to make the mixture. Furthermore, the mixture was subjected to the same compacting and sintering as in Example 1 to form pellets. Table 2 shows the relationships between the fabrication conditions of pellets and the physical properties of the pellets. As is clearly seen from Table 2, the pellets having the excellent physical properties are fabricated by using the above-described pore-former agents and lubricants in the process according to the present invention. TABLE 2 __________________________________________________________________________ Grain Size of Pellets Pore-Former Agent Lubricant (.mu.m) __________________________________________________________________________ C 1 D 2 50.2 C 2 " 48.6 C 3 " 49.3 C 4 " 52.9 C 5 " 49.4 C 6 " 51.1 C 1 + C 4 " 49.5 C 1 + C 2 + C 4 " 48.3 C 1 + C 2 + C 3 + C 4 " 49.9 C 1 + C 2 + C 3 + C4 + C 5 " 49.7 C 4 D 1 51.3 " D 3 50.4 " D 4 48.5 " D 5 51.1 " D 6 49.7 " D 7 50.3 " D 1 + D 2 50.5 " D 1 + D 2 + D 3 49.8 " D 1 + D 2 + D 3 + D 4 50.9 " D 1 + D 2 + D 3 + D 4 + D 5 52.2 " D 1 + D 2 + D 3 + D 4 + D 5 + D 6 50.5 " D 1 + D 2 + D 3 + D 4 + D 5 + D 6 + D 7 49.8 __________________________________________________________________________