NEPTUNIUM INCORPORATION INTO URANIUM(VI) COMPOUNDS FORMED DURING AQUEOUS CORROSION OF NEPTUNIUM-BEARING URANIUM OXIDES

摘要

We report results of experimental studies on the behavior of Np during aqueous corrosion of unirradiuted Np-bearing U oxides. Np-doped U oxides were reacted in humid air at 90℃ and 150℃ for several weeks within sealed stainless-steel vessels. Reacted solids were examined by scanning and transmission electron microscopies (SEM and TEM), electron energy-loss spectroscopy (EELS), and X-ray powder diffraction (XRD). Dehydrated schoepite, (UO_2)O_(0.25-z)(OH)_(1.5+2z) (0 ≤ z ≤ 0.15), is the predominant U(VI) compound formed in these experiments. Preliminary EELS analysis on crushed grains verify that dehydrated schoepite formed at 150℃ contains up to approximately 2 wt.% Np, corresponding to a maximum Np:U molar ratio of approximately 1:40. These are maximum values because the degree to which surface-sorbed Np is present on the grains analyzed is not yet known. Crystalline NpO_2 also precipitated during these experiments, and the concentration of Np in dehydrated schoepite may represent the maximum amount of Np that can be incorporated into dehydrated schoepite under the experimental conditions.