Oxygen isotopes of fuel pellets from the fifth collaborative materials exercise and uranium oxides reference materials determined by continuous flow laser fluorination mass spectrometry for nuclear forensic applications

Abstract

Uranium oxides are essential materials in the production process of nuclear fuel for civilian or military applications. As such, identifying their geological origin, manufacturing process and age, plays a central role in the field of nuclear forensic. This study aims to expand the traditional characterization analytical techniques by measuring the oxygen isotopic composition of various uranium oxides (e.g., UO2, U3O8), uranium ore concentrates (UOC). We apply it to UO2 pellets from the Fifth Collaborative Materials Exercise (CMX-5). We developed an accurate laser fluorination in line with continuous-flow mass spectrometry analytical method for measuring oxygen isotopes in sub-milligram nuclear materials, including raw materials and selected materials from several stages of the fuel production cycle. We report for the first time, on the oxygen isotope composition of the two UO2 fuel pellets, used for the international CMX-5. We show that δ18O of these pellets differ by 1.7‰, which probably originates from their manufacturing processes. CUP-2, a UOC, was used to demonstrate the challenge of measuring isotope composition of hydrated forms of uranium oxides. U3O8 was found to exhibit lower than expected, by stoichiometric formula, oxygen contents. That might originate from oxygen loss during the pre-fluorination process, or indicates the presence of more than one phase within this particular U3O8 system.