Nuclear forensic applications of uranium oxide chemistry and morphology

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The entire nuclear fuel cycle is a chemistry-intensive process, from accessing the raw materials from ore, to enriching and forming the fuels, to the eventual long-term disposition or reprocessing of the spent fuel. This chemistry is vital to nuclear forensics, as the chemical history of a sample imbues it with unique signatures that should provide insight into the processing and conversion a sample has undergone. Of course, now that many countries have had nuclear programs for decades, it is appropriate to question the stability of these chemical signatures. This necessitates the assessment of what new chemical and morphological signatures are introduced by the aging in bulk uranium oxide samples, and whether those signatures can be used to elucidate the conditions under which the materials were stored. This thesis is concerned with the analysis of uranium oxide samples: both high-purity UO2, alpha-U3O8, and alpha-UO3 samples, and several legacy U3O8 and UO3 samples. The samples were aged over several years in chambers designed to control temperature and relative humidity. There are two primary focuses for analysis of these aged uranium oxides -- the first is the identification of chemical signatures using powder X-ray diffraction (p-XRD) and extended X-ray absorption fine structure (EXAFS) analysis, and the second is the identification of morphological signatures contained in scanning electron microscopy (SEM) images using a standardized lexicon for consistent textural analysis. LA-UR-15-26762.