STUDY OF THE PROPERTIES OF AMMONIUM POLYURANATE PRECIPITATES AND UO2 POWDERS AND PELLETS OBTAINED WITH DIFFERENT TECHNOLOGIES

The results of a differential-thermal analysis are used to compare the properties of ammonia polyuranate precipitates, UO2 powders and pellets, obtained by different methods as well as metallic uranium. It is found that the phase NH3 center dot 3UO(3)center dot 5H(2)O forms in regular precipitation of ammonium polyuranate. When using nanotechnology, the phases NH3 center dot 2UO(3)center dot 3H(2)O and 4NH(3)center dot 6UO(3)center dot 8H(2)O are also present in the precipitate. UO2 powder prepared from such precipitate has high activity, since all phase transformations in it occur at a lower temperature. Modified fuel pellets of uranium dioxide, which are obtained by means of nanotechnology or mechanical addition of ammonia-containing reagents to powder, differ from the standard powders by a lower rate and more complex mechanism of oxidation, similar to metallic uranium. Modified UO2 fuel pellets fabricated at the Physics and Power-Engineering Institute, are now undergoing tests in the BOR-60 reactor. After tests on the irradiated new modified fuel have been completed, it will be possible to judge its reliability.