GB910212A - Uranium oxide sols - Google Patents

Abstract

A hydrothermally stable urania sol. in which the uranium is in the plus IV oxidation state, is produced by gradually removing by hydrolysis anions from an aqueous solution containing uranium tetrachloride until the solution is substantially free from electrolytes. The anions may be removed by dialysis using an anion permeable membrane. The starting material is an aqueous solution of uranium tetrachloride or of another salt which can be converted to uranium tetrachloride under the conditions of the process, e.g. uranyl nitrate. In a preferred procedure the solution is maintained at an elevated temperature, preferably 60 DEG to 100 DEG C., in a reservoir and gradually fed first to the anion removing station, where the solution temperature is preferably 15 DEG to 35 DEG C., and then back to the reservoir, the operation being continued until the solution is substantially free from electrolytes. The concentrated sol. may be diluted to any desired lower solids content by the addition of deionized water or water of low ionic content. The sols. may be clad with silica to a thickness of 30 to 120 Angstroms to improve their hydrothermal stability, the cladding being effected by adding a silica sol. to the urania sol. preferably followed by stabilization of the product by heating under non-evaporative conditions in the presence of an alkali metal hydroxide, e.g. sodium hydroxide which is stable under reactor conditions and which contains elements of low thermal neutron cross-section. The diameters of the particles in these sols. are from 60 to 1900 Angstroms. According to the Examples:- (1) Uranium tetrachloride solution was heated to 80 DEG C. in a vessel, withdrawn at the rate of 150 ml./min., cooled so that the cell temperature was maintained at 18 DEG to 27 DEG C. and pumped into the cathode compartment of an electrodialysis cell separated from the anode compartment by an ion-exchange resin membrane. The solution leaving the cell was heated to 80 DEG C. and returned to the original vessel, the circulation being continued for 9 hours with a break after 3 hours to remove some of the excess HCl from the solution and to dilute it with deionized water. The sol. had a specific conductivity of 1,36 X 10-4 mho/cm. and the diameters of the particles ranged from 60 to 700 .s. (5) A urania sol. prepared as in example 1 was coated with silica by adding rapidly, with mixing, a silica sol. to the urania sol. heated at 40 DEG C. The silica sol. containing 2% of SiO2 was made by passing a sodium silicate solution through a column containing a cation-exchange resin in the hydrogen form. The weight ratio of UO2 to SiO2 in the cladding operation was 2,2:1. After refluxing and cooling the urania clad sol. was deionized by passing it through an ion-exchange resin.