| 摘要 |
Uranium dioxide is prepared by treating a solution of uranyl and fluoride ions with an aqueous solution of ammonium hydroxide at an ammonium-to-uranium ratio of at least 25 to 1, with thorough agitation, removing the resulting precipitate and contacting with steam at a uniform temperature of 400 DEG to 650 DEG C. to give U3O8, which is reduced with hydrogen at 550 DEG to 600 DEG C. to give UO2. The UO2 may be contacted with air until an oxygen-to-uranium ratio of at least 2,08 is obtained. The original solution may be uranyl nitrate solution with fluoride ions supplied by adding HF, the amount of fluoride being at least equivalent to the stoichiometric amount present in the compound uranyl fluoride. The precipitation, preferably at 25 DEG C., may be effected by either batch or continuous techniques. The precipitate is preferably contacted with steam in a kiln-type reactor or a fluidized bed reactor. The U3O8 is preferably contacted with hydrogen diluted with an inert gas such as nitrogen in a rotating kiln, screw type reactor, or a fluidized bed reactor. The UO2 having an oxygen/uranium ratio of 2,04 may be reoxidized to a ratio of 2,08 to 2,12. The resultant UO2 has a surface area of 5-8 square metres/gram and may be fabricated into fuel pellets for a nuclear reactor by compressing into shapes at a pressure of at least 5,00 pounds per square inch and maintaining the resultant shapes at a temperature of over 15000 DEG C., preferably at 1800 DEG C., in a hydrogen atmosphere until sintering of said shapes is complete. The UO2 may initially be compressed into pellets of up to several inches diameter, and then coarsely ground before final pellet formation. Specification 852,979 is referred to. |
