Study on the Thermal Stability of the Na₂UF₈ Complex in the Argon Atmosphere

Abstract

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.