Preparation of sodium uranates

In order to estimate the fuel behavior during a severe accident in a fast reactor, it is necessary to make pure sodium uranates and to measure their properties. In the present study, sodium uranates (Na_xU_yO_z) were synthesized at various reaction temperatures for various durations using UO₂ and Na₂O or Na₂CO₃. We succeeded in synthesizing nearly pure sodium uranates such as Na₂U₂O₇, α-Na₂UO₄, NaUO₃, and Na₄UO₄. Information for making α-Na₂UO₄ and NaUO₃ with higher purity was obtained. The phase transition temperature from the α-phase to the β-phase of a sample of Na₂U₂O₇ was clarified to be 658.2 K by thermal expansion measurement. (author)