Discoveries related to uranium oxide may support nuclear nonproliferation

Researcher Tyler Spano examines a sample of uranyl nitrate solution that she uses as a precursor to many uranium oxide syntheses. (Image by Carlos Jones/ORNL, US Dept. of Energy).

Researchers at the Oak Ridge National Laboratory examined four previously understudied phases of uranium oxide: beta (β-), delta (δ-), epsilon UO3 (ε-UO3) and beta U3O8 (β-U3O8) and noted that each phase has a unique fingerprint that can reveal when something out of the ordinary happened to lead to its creation, helping organizations such as the International Atomic Energy Agency investigate unintended mistakes or blatant misuse of nuclear material.

Many uranium oxide phases were identified decades ago but had remained loosely understood. The α phase of U3O8, for example, is common, but the β phase is formed under unusual conditions.

Researcher Tyler Spano and her colleagues used analytical methods to observe uranium oxides under different conditions. X-ray diffraction helped them identify the chemical phase of materials. Optical vibrational spectroscopic techniques, such as Raman and infrared, enabled them to observe the chemical structure on shorter length scales, which can be used to identify small quantities of these materials.

“The way UO3 moves through the exotic phases is a little unusual,” head researcher Andrew Miskowiec said. “My team is working on the foundational science to be able to identify these materials if we observe them in the real world and to understand the unusual conditions that led to how they were formed.”

According to Miskowiec, the discoveries from this research also support science beyond national security missions. Specifically, the structure of ε-UO3 is of interest for novel reprocessing methods being investigated elsewhere. The detailed knowledge of the structure of this phase is useful in understanding the material’s physical properties and performing reaction rate measurements.

The scientist pointed out that he and his group will continue to explore new ways to catalogue materials used in the nuclear fuel cycle. For example, the mysterious amorphous phase of UO3 doesn’t have long-range crystallographic order. As a result, the structure can’t be examined using X-ray diffraction, but information can still be obtained from the Raman spectrum.

“Some of these compounds are made from specific processes, which gives us a very specific piece of information,” Miskowiec said. “It’s not only important to identify the compound, but also to have an understanding of its formation conditions.”