The preparation of the nuclear fuels such as uranium and its compounds starting from the yellow cake or ammonium uranate, (NH.sub.4).sub.2 U.sub.2 O.sub.7, usually follows a series of chemical and metallurgical processes at relatively high temperature and under strictly controlled experimental conditions. The flow-sheet of the overall processes for UO.sub.2, UC and U.sub.2 N.sub.3 are shown diagrammatically as follows. ##STR1## where the solid lines indicate the conventional processes, while the dotted lines show the reaction paths developed in the present invention.
Taking uranium dioxide as an example, the conventional method comprises denitration and subsequent hydrogen reduction and gives forth to a uranium dioxide which is often found to be nonstoichiometric, strict control of the reaction temperature, grain size of UO.sub.3, composition and flow rate of the reacting gas etc. is therefore necessary. In contrary, a stoichiometric uranium dioxide could easily be obtained by reacting uranium amalgam with water vapor within a wide temperature range of 500.degree.-700.degree. C.
Taking uranium carbide as the second example, the conventional method of reacting uranium dioxide and graphite powder, both in solid form, necessitates a very high reaction temperature well above 2000.degree. C. Moreover the involved phase separation after the reaction renders the stoichiometricity of the product difficult. Another gas-solid reaction process involving a fine uranium powder and methane is seldom adopted, because of the tedious process to obtain the uranium powder. In the present invention the chemically active uranium powder obtained from the decomposition of uranium amalgam reacts readily within a wide temperature range of 500.degree.-700.degree. C. to form a stoichiometric uranium monocarbide, UC, as identified with x-ray diffractometry and density measurement. However, it must be pointed out that at a temperature higher than 700.degree. C., uranium dicarbide, UC.sub.2, was observed in the product.
Taking uranium nitride as the third example, although the applicability of this compound as a nuclear fuel is limited, it is to show that the chemically active uranium powder obtained from the uranium analgam even reacts with the chemically inert nitrogen within the same temperature range to form uranium nitride with a chemical formula of U.sub.2 N.sub.3. It has further been observed that this compound decomposes into UN at a temperature higher than 1000.degree. C.
The overall process for the above mentioned compounds will thus be sgreatly simplified as compared with the conventional chemical and metallurgical process and ensure an economical advantages by greatly reducing power consumption and initial costs for the set-up.