Study on the Thermal Stability of the Na(2)UF(8) Complex in the Argon Atmosphere

[Image: see text] The Na(2)UF(8) complex is an important intermediate compound in the purification of UF(6) by the adsorption–desorption process during fluoride volatility of the spent nuclear fuel, and its decomposition is seriously affected by temperature and atmosphere. In this study, the thermal stability of Na(2)UF(8) in the argon atmosphere was investigated by the in situ Raman spectroscopy. The decomposition products of Na(2)UF(8) at different temperatures were systematically determined by X-ray diffraction spectroscopy and X-ray absorption fine structure spectroscopy. The results indicated that Na(2)UF(8) on the NaF sorbent was stable under 300 °C in the argon atmosphere, and it started to decompose into UF(6) and NaF rapidly when the temperature was above 300 °C. Meanwhile, a small amount of Na(2)UF(8) was converted to Na(3)UF(7), and it was stable in the temperature range from 350 to 450 °C. The decomposition mechanism of the Na(2)UF(8) and the formation mechanism of Na(3)UF(7) on the NaF sorbent were speculated according to the experimental results.