Nuclear forensics is a field of science that requires a suite of analytical techniques to obtain information on the origin and intent of intercepted nuclear material. Previous studies have focused on understanding how initial feed material, calcination temperatures, and precipitation conditions alter the morphological characteristics of uranium oxides within the nuclear fuel cycle. However, not many studies have been conducted looking at changes in morphology as a function of time under environmentally relevant storage conditions and to date, no study has been published on the post-storage morphological changes of transuranic material. This work aims to determine if and how temperature and relative humidity alter the initial phase and particle morphology of a series of actinide oxides (ThO2, UO2, PuO2) and ideally, will lead to a conceptual model describing their aging as a function of time under controlled storage conditions. Morphological changes were monitored using scanning electron microscopy (SEM) and interpreted utilizing a previously published lexicon of descriptive imaging terminology. Changes in phase were observed using a novel powder on single crystal X-ray diffraction (SC-XRD) technique. Results show ThO2 exhibits no change in its macroscopic appearance and microstructure whereas over a period of two years, PuO2 undergoes a recurring transition to lower symmetry followed by recrystallization at high temperature and high relative humidity. This speaks to plutonium’s kinetic stability, puts into question the use of thorium as a plutonium analog, and underscores the solid-state complexity in relation to nuclear forensic signatures.

Environmental aging of actinide oxides under controlled storage conditions

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.