| Popis: |
The reactivity and reaction conditions to form lithium and sodium uranates were studied in an attempt to grope some useful head-end processes in nuclear fuel reprocessing. In the reactions between alkali metal carbonates and U3O8 in air at 800°C, the products with Na/U ratios 0.8 and 0.857 gave the same X-ray diffraction patterns in which the peaks of α-U3O8 were almost not detected. The observed peaks for uranates with Li/U = 1.205, 2, 4 and Na/U = 1 are well consistent with the values reported previously. No indication of formation of Li2U6O19, Li6UO6 and Na4UO5 was observed. Thermogravimetric observations on the reactions between the carbonates and U3O8 revealed that they consisted of two processes, i.e. (1) the formation of uranates and (2) the oxidation of the uranates formed. The rate of reaction (1) was higher than that of reaction (2) when the M/U ( M = Li, Na ) ratio was 0.5. When the ratio was 1, the rate of reaction (1) lowered and became rate determining. The reactions between alkali metal nitrates and UO2 showed that the minimum M/U ratios for obtaining the uranates without U3O8 were 0.667 and 0.8 for lithium and sodium uranates, respectively. They were formed by heating at 600°C for 3 h in oxygen or air. Mixing process of initial materials is not required for these reactions. The uranates formed were found to be dissolved in 1 M HNO3 within 1 min. |
