Investigations into the polymorphs and hydration products of UO₃

This work focuses on progress in gaining a better understanding of the polymorphic nature of the UO3 and UO3-water system; one of several important materials associated with the nuclear fuel cycle. The UO₃-water system is complex and has not been fully characterized, even though these species are common throughout the fuel cycle. For example, most production schemes for UO₃ result in a mixture of up to six different polymorphic phases, and small differences in these conditions will affect phase genesis that ultimately results in measureable changes to the end product. Here we summarize our efforts to better characterize the UO₃-water system with optical techniques for the purpose of developing some predictive capability of estimating process history and utility, e.g. for polymorphic phases of unknown origin. Specifically, we have investigated three industrially relevant production pathways of UO₃ and discovered a previously unknown low temperature route to β-UO₃. Powder x-ray diffraction and optical spectroscopies were utilized in our characterization of the UO3-water system. Pure phases of UO₃, its hydrolysis products and starting materials were used to establish optical spectroscopic signatures for these compounds. Preliminary aging studies were conducted on the α-and γ- phases of UO₃.