Powderization behavior of uranium dioxide solid by non-equilibrium plasma oxidation

The amounts of actinide and isotope ratios of actinides in the nuclear fuel debris from the Fukushima accident are required to known for the determination of the plan of the treatment and disposal of nuclear fuel debris. For these analyses, the dissolution of debris, and the nuclide separation are necessary.

Now we have proposed that these substitutes are chemically converted into easily soluble substitutes by thermochemical reactions. In order to promote the dissolution of these insoluble substances, the powderization is required. Thermal oxidation can lead to the powderization of solid uranium dioxide and the volatilization of volatile radioactive materials. it is desirable to cause oxidation reactions under the milder conditions for analysis. We therefore developed a non-equilibrium plasma oxidation device to verify the powderization of uranium dioxide solid under lower temperature condition and to compare the results with thermochemical oxidation. we confirmed the powderization of uranium dioxide solid, and that uranium dioxide was converted to triuranium octoxide by XRD. We found that the particle size distribution is obeyed the logarithmic normal distribution with 30.32±20.07μm.From results of SEM observation, the very small uneven bumps of 1µm or less appears on the surface of powders was observed, therfore, the increasing the surface area required for dissolution or chemical conversion to soluble compounds can be expected.

As a conclusion, a plasma oxidation reactor using non-equilibrium plasma was developed and the feasibility of the powderization of solid Uranium Dioxide material was possible with a lower temperature(less than 200℃) compared to the thermochemical oxidation (350-650℃).