The effects of certain process variables on the production of uranium tetrafluoride from U3O8 on the 250 g. (uranium) scale, and smaller scales in a few cases, have been studied. It was found that the initial step (reduction of U3O8 to UO2 by hydrogen) is essentially complete in 15 minutes at 700 degree C. The rate of conversion was shown to be temperature dependent, the greatest increase in rate of conversion occurring in the vicinity of 500 degree C. In the conversion of UO2 to UF4 by hydrogen fluoride, the optimum temperature was found to be abut 600 degree C. For a reaction time of 5-1/2 hours, both higher and lower temperatures yielded less completely converted products. An increase in rate of conversion, both in reduction and hydro-fluorination, resulted when smaller quantities of material were used. Changes resulting from the present study and yielding an increased efficiency in the production process are described.

The index of refraction of PuO2 made by thermal decomposition of PU(C2O2, 6H2O gradually increases from a value < 1.9 to 2.40 as the decomposition temperature is increased from 150 degree to l000 degree C. This change in refractive index parallels a gradual change in the x-ray diffraction pattern from weak, diffuse lines for PuO2 ignited at 150° to sharp, well resolved lines for PuO2 ignited at 1000°C. Similar results are observed for PuO2 made by thermal decomposition of Pu2(C2O4)3*11H2O. The refractive index of PuO2 made from Pu metal at 170°C is 2.40 and is not affected by further ignition at higher temperatures, although crystal growth does occur. The rate of solution of PuO2 in an HCl-KI solution is greatest for samples prepared at low temperatures and decreases markedly for oxides ignited at higher temperatures. These observations hive been interpreted to mean that ignition at higher temperatures causes a gradual perfection of the originally highly distorted and impurity-containing PuO2 lattice obtained by low temperature decomposition of the oxalates and promotes the slow growth of crystallites. Both factors decrease the reactivity of the PuO2.