Small, ceramic urania spheres can be prepared for use as nuclear fuel by internal chemical gelation of uranyl nitrate solution droplets. Acid-deficient uranyl nitrate solutions up to 3.4 M in uranium with N03'/U mole ratios of 1.5 to 1.7 are prepared by dissolution of U308 or U03. Decomposition of hexamethylenetetramine dissolved in the uranyl nitrate solution releases ammonia to precipitate hydrated U03. Previously established flowsheet conditions have been improved and modified at ORNL and have been applied to prepare dense U02 spheres with average diameters of 1200, 300, and 30 pm. The 1200and 300-^m U02 spheres were prepared by gelation in trichloroethylene at 50 to 65 °C; 2-ethyl-1-hexanol was used as the gelation medium to prepare 30-;um U02 spheres.

Two methods were used to measure the vapor pressures of zirconium tetrachloride and hafnium tetrachloride over the range from 10 to 10,000 mm Hg. The lower pressures (10-1000 mm) were measured in a nickel diaphragm apparatus1 which has been used successfully on other compounds by this laboratory and others2 recently. The higher pressures were obtained using a modification of the capillary "bridge" apparatus which was used by the U. S. Bureau of Mines3 in the extensive investi gation of the vapor pressures of common metal chlorides.The charge materials were prepared from oxides purchased from De Rewal International Metals Company. The ZrO2 contained less than 0.1 per cent HfO2 and the HiO2 was 98.7 per cent pure.l The oxides were purified by a mandelic acid precipitation4 to remove impurities such as iron, titanium, and calcium.The vapor pressure curves of both salts are shown on the accompanying graph. The equations for the curves are: zrci4 10g P = -5'Ír00 + 11.76Hfc14 log P = -sïooThe melting points were found to be 437°C for ZrCl4 and 434°C for HfCl4.By extrapolation, the vapor pressure of ZrCl4 at its melting point is 14,500 mm, and the vapor pressure of HfCl4 at the same temperature is 25,000 mm.The data of this report are in close agreement with and appreciably extend the range of the data of the Ames Laboratory.5The investigation of the high pressure range is being continued and it is hoped that it will be possible to obtain data above the melting points in the near future. In any event, this brief memo randum will be followed by a complete technical report which will be issued before January 1, 1950.

No abstract

Gel spheres containing U03, (Th,U)0*, Al203, Al203-Zr02, and mixtures of various other metal oxides (including Fe, Zr, Al, and Si) have been produced by the internal gelation process by the same general flowsheet. In the internal gelation process, hexamethylenetetramine (HMTA) decomposes to produce ammonia which precipitates hydrous metal oxides gels. The process conditions (metal molarities, HMTA/unneutralized metal ratio, urea/metal ratio, and gelation temperatures) are within the same ranges for all of the products. Selection of the feed compositions and process conditions can be guided by the general criteria described, but optimum conditions need to be determined empirically. General process requirements are discussed in detail, and products made under these conditions are described.

No abstract