Patent Number: 041939530
Section: description

Examples of the process of the invention are set forth below. The hydrosols having high concentration of heavy metal are produced as follows. ThO.sub.2 hydrosols are quite simply produced by addition of gaseous or dissolved ammonia to solutions of Th(NO.sub.3).sub.4. The precipitate thus produced can easily be collodially suspended by stirring at increased temperature, preferably at 95.+-.10.degree. C. After introduction of 80-90% of the aqua ammonia quantity which is necessary for a complete precipitation, an aquasol is obtained in which the precipitation is almost reached. The sols are stabilized by hydrogen ions and have a pH value of about 3. For the production of the mixed oxide grains of (Th,U).sub.2, up to a Th:U ratio of 3:1, solutions can be used as starting materials for the sol production that contain UO.sub.2 (NO.sub.3).sub.2 in addition to Th(NO.sub.3).sub.4. EXAMPLE 1 2.5 moles of Th(NO.sub.3).sub.4.5H.sub.2 0 were dissolved in 0.5 liter of H.sub.2 O and the solution was heated to 80.degree. C. Beginning at this temperature, NH.sub.3 gas was introduced through the shaft of the stirrer. The temperature then rose as a result approximately to the boiling point of the solution of about 110.degree. C. After an hour 85% by weight of the amount of ammonia gas necessary for the complete precipitation reaction had been introduced. In the course of an additional hour, an additional 5% amount of ammonia by weight was gradually introduced. After cooling the hydrosol was filled out with H.sub.2 O to the volume of 1 liter. The hydrosol thus prepared was cloudy-white and at 20.degree. C. had a viscosity of .eta.=8 cP and a pH value of 3.5. This hydrosol was dripped in a drip casting column having at the bottom a precipitation bath containing aqua ammonia and thereabove an ammonia-containing gas phase. The hydrosol was injected in drop form at 40.degree. C. horizontally into the gas phase at a velocity allowing the drops to fall through the gas phase by gravity until they fell into the precipitation bath. The height through which the drops fell in the drip casting column was 5 cm. The height was so chosen that the prehardening of the drops in the gas phase is just sufficient to prevent permanent deformation of the drops upon hitting the surface of the precipitation bath. The hydrosol was drip-cast at a drop frequency of 400 HZ with a drop diameter of 1.24 mm. The precipitation bath contained 5 moles per liter of ammonium nitrate and 1% by weight of ammonium hydroxide. The gel spheres produced in this manner were washed free of ammonium nitrate with water that contained 0.01% of surfactant which is available under the common commercial designation "Span 80" and was then dried at 250.degree. C. at an atmosphere containing water vapor. The cores of ThO.sub.2 thereafter sintered had a diameter of 500 .mu.m with good spherical shape, and a density of 99.8% of that theoretically possible. The yield was 99.9%. EXAMPLE 2 2.4 moles of Th(NO.sub.3).sub.4.5H.sub.2 O were dissolved together with 0.6 moles of UO.sub.2 (NO.sub.3).sub.2.6H.sub.2 O in 0.5 liter of water that had been heated to 80.degree. C. and--as described in Example 1--was converted to a hydrosol of 1 liter. The prepared hydrosol that had an intense dark red color, had a viscosity of 6.5 cP. The pH value measured was 3.2. The hydrosol--warmed to a temperature of 30.degree. C.--was drip-cast in the same manner as in Example 1. The washing and drying of the gel spheres was also carried out in the same manner as in Example 1. The high temperature treatment, however, was carried out so as to reduce the hexavalent uranium to tetravalent uranium, in a reducing atmosphere of argon with 4% by weight of hydrogen. The results were comparable to those of Example 1. EXAMPLE 3 1.5 moles of Th(NO.sub.3).sub.4.5H.sub.2 O were dissolved in hot water of a temperature of 80.degree. C. and--as described in Examples 1 and 2--converted into a ThO.sub.2 hydrosol of a volume of one liter. The hydrosol had a pH value of 4.0 and a viscosity of 10 cP. The hydrosol was drip-cast at a temperature of 60.degree. C. The remaining treatment corresponded to that given in Example 1. The sintered ThO.sub.2 granules had a diameter of 400 .mu.m. The performance of the process with an ammonia-hydroxide concentration in the precipitation bath in the range between 3 and 5 moles per liter brought about comparable results. In addition to use for the production of fuel and breeder particles of thorium oxide or granules containing thorium-uranium mixed oxides, it is also possible to apply the process to the manufacture of thorium-plutonium mixed oxide granules. Although the invention has been illustrated by means of particular examples, it is evident that variations and modifications are possible within the inventive concept.